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View Full Version : Upper Receiver Flex Testing - Part Two



K.L. Davis
06-07-06, 18:20
Here is the rest... work continues on this, see the comments at the bottom.

------------------------------------
Test Two -- This was a duplication of the first test, this time with the upper receiver supported by "pinning" into a fixture that represents a lower receiver.

Conventional (non-supported) Receiver
http://img495.imageshack.us/img495/7978/pcdv0062small8bs.jpg

Findings - Here we see an increase in all of the measurments, with a noticable increase in the deflection of the chamber gauge -- further indication that the flexing of the front of the receiver is valid and demonstrable... but are the measurements enough to support a real concern?
http://img154.imageshack.us/img154/6749/testtwo7bu.jpg

------------------------------------
Test Three -- Leaving everything in place and under load from Test Two, I used a small torch to apply heat the barrel nut/chamber area of the upper receiver assembly. Lightly feathering only the chamber area with the torch, I took the temperature to 200 - 220 deg (F) -- not at all an unrealistic temperture for the rifle. The results here were very interesting, the dial gauges reacted immediately to the heat. As this was still an elastic state for the metal, it was interesting to watch as the upper cooled... the measurements returned to the original readings of Test One as the receiver returned to room temperature.

This test (I believe) induced enough alignment error to believe that not only the reliability, but the structural integrity of the weapon may have been compromised.
http://img230.imageshack.us/img230/1976/testthree2kz.jpg

------------------------------------
More Theory -- I had fully expected to see the results that I had seen up to now... I suspect that the defining moment of this problem was actually the removal of the carry handle. The time frame for the apparent increase in some of the issues attributed to the "receiver flexing" does seem to fall in line with the increase in flat top uppers being available. While perhaps not designed that way, the handle is a integral arch that ties the front of the receiver to the rear anchor point (take down pin) and we sill see, adds a LOT of rigitity to the upper receiver.

------------------------------------
Test Four -- An A2/Carry handle upper is built with the same parts as the flat top and pinned in the same fixture. I went straight to the twenty pound test with this...

http://img226.imageshack.us/img226/9895/pcdv0089small3ly.jpg

Findings - The carry handle appears to stiffen the upper receiver a great deal, the deflection at the chamber cauge was actually just over one-onethousandths of an inch!
http://img507.imageshack.us/img507/3088/testfour2rb.jpg


------------------------------------
Test Five -- The next test was with a "piggy back" type mounting handguard... for this test I used a CAS-V system from Vltor on a CMT/Stag M4 style upper -- again, I went straight to 20 pounds on the test.

http://img369.imageshack.us/img369/7735/pcdv0104small8pi.jpg

Findings - Although there was a lot of flex in the handguard, note the chamber gauge deflection was very close to the A2 Carry Handle upper at just slight less than 1.5 thousandths of an inch!
http://img234.imageshack.us/img234/2633/testfive7es.jpg

------------------------------------
Test Six -- Of course the test would not be complete without a look at the new monolithic upper receivers... I only had one such part in my hands during the test, but decided to see how it does.

http://img228.imageshack.us/img228/2714/pcdv0096small3fp.jpg

Findings -- I am going to hold off of specific measurements right now, as the unit I have is a prototype and I am told the production piece will be slighty different... I also hope to compare other entries in the monolitic catagory in a side-by-side match up.

To be fare to everyone though, I will say that both readings were better than those recorded under the twenty pound load on the fully supported receiver in Test One.

I can say that it is very rigid... the monlitic design appears to offer a far more rigid handguard section than is avaiable from any of the above combinations and the measurable receiver flexing is far less than what was noticed from the current flat top upper and barrel nut mounted hand guard systems.

update: the readings for the prototype VIS were handguard deflection of 0.011 and chamber gauge was 0.004

------------------------------------
Test Seven -- A test of a new issue KAC RIS system was interesting...

http://img446.imageshack.us/img446/2536/cimg0527small3oe.jpg

Findings - The RIS did very well really, this is mostly for comparison, but the handguard deflection was 0.0014 and the chamber gauge deflection was 0.007 -- this is about as good as the fully supported receiver in Test One and better than the unsupported receiver in Test Two.

------------------------------------
Conclusions -- This is not the end of the testing... but offers some pretty telling evidence. As stated, I hope to do more side-by-side testing with the monlithics in the near future, as well as some range time with different designs (I have designed a jig that will intentionally stress the upper receivers and see if I can not get them to break!) -- but for now, I feel comfortable with the folowing.

The upper receiver "flexing" issue seems to be real... I believe that the removal of the carry handle does make the platform subceptable to "bowing" the upper enough that it could effect the reliability or integrity of the weapon.

Granted, this will vary from rifle to rifle and is something that most likely would only be experiencd by a shooter that is a very stressful situation and has fired the gun to the point of being quite hot... but this seems like the absolute worst time for it to happen. This flexing also seems to only be an issue on guns that use a barrel nut mounted handguard system.

All of this is most likely a non-issue for 99.9% of the people reading this... The likelyhood that the combination of the weapon configuration, individual user and appropriate situation will all come together exists almost solely on the battlefield... and even there is would have to be the exception rather than the rule -- but, if you prepare for the worst, it is not as much of a surprise when it happens.

Some other notes:

The strongest upper is the old A1/A2 carry handle upper -- I did not test a removable carry handle or one piece optic mount as a possible "bridge" on purpose... as I felt that even if it did stiffen the upper receiver, it would only be as good as its current mounting and can not be relied on as a remedy.

The carry handle also seems to serve well as a heat sink... more on that in the future perhaps.

Yes, there is someone already working on a receiver that uses an itegral optics platform to strengthen the upper... as well as a few lesser known things already out there.

The "piggy back" style handguards do not stress the barrel nut, while it is debatable if they actually provide an additional rigidity to the top spine of the upper receiver, the example used in this testing did not seem to flex the upper receiver. These systems however, do seem to have as much or more rail flex than the current barrel nut mounting designs.

02MAR06 - No doubt that the missing carry handle weakens the receiver... some model work indicates that the "sidewalls" of the upper receiver provide little reinforcement -- the starboard side is a washout with the ejection port taking a large piece of the structure away and it seems that the weak spot on the port side is just below the cut for the cam pin to clear. Most likely the sides are bowing out under load (in the area indicated in the pisture) and the only real support is the top section of the receiver, which allows the front section to flex as it pivots on the front takedown pin.

http://img492.imageshack.us/img492/9582/receiver6zr.jpg

07JUN06 - Finally get to put this back where people can see it! Computer models confirm the idea that the receiver is bending just behind the front lug under load. Some idea for a reinforced receiver are being looked at. I will keep this updated as I get new stuff.

POF-USA
06-07-06, 22:13
K.L. Davis,

Great information!

I hope to read more testing with heat from you.
Weapons heat up if shot hard and fast (Example: Beta-C dumps in full auto).
Your test seem to indicate that the hotter the weapon gets
the more the chamber indicator would show movement.

I wonder how much movement/flex of the chamber indicated reading you would have, when the weapon is hot and using a vertical grip mounted at the front of the rail system and pulling it toward the receiver?

Just a suggestion that you may want to try:
Maybe you can test this by vertical mounting your upper receiver and fixture,
then install the vertical grip at the muzzle end of the rail system, then hang weights off the vertical grip.
Use a torch and a infered heat sensor gun to record heat and indicate movement in the chamber. This type of a test would reflect how a weapon system using a vertical grip may induce movement/flex in the upper receiver when the weapon system is hot.

Keep up the great work here. Your information will help others. :D
Best regards,

Frank
Patriot Ordnance Factory (POF-USA)

Boom
06-08-06, 11:58
Mr. Davis excellent post. I look forward to reading more of it this weekend.

Forest
06-08-06, 12:19
Frank,
Instead of vertically mounting the upper, which changes the the setup, and any gravity effects (even if minimal). Why not use a pully? Tie a cord to the VFG run it over a pully then tie the weights to the cord.

This is the idea (excuse the crude graphics):
http://groups.msn.com/_Secure/0VgDdArcb5NQPiuTteEXLAg96LymonNzhQK5MAa78OTabvDhy52S!9DXUy5BtWRO!W!IEqnTAyVFuhhJyCnuYSlxiy969J1Hyau05y2AdjFY4lcVQvAcbUJGOglcQWyZM/Test%20Proposal.jpg?dc=4675575950455389026

Mr Davis,
Thanks for posting these threads! I had been wondering how your experiments were going.

K.L. Davis
06-08-06, 23:10
Frank,
Instead of vertically mounting the upper, which changes the the setup, and any gravity effects (even if minimal). Why not use a pully? Tie a cord to the VFG run it over a pully then tie the weights to the cord.

This is the idea (excuse the crude graphics):
http://groups.msn.com/_Secure/0VgDdArcb5NQPiuTteEXLAg96LymonNzhQK5MAa78OTabvDhy52S!9DXUy5BtWRO!W!IEqnTAyVFuhhJyCnuYSlxiy969J1Hyau05y2AdjFY4lcVQvAcbUJGOglcQWyZM/Test%20Proposal.jpg?dc=4675575950455389026

Mr Davis,
Thanks for posting these threads! I had been wondering how your experiments were going.

I have a real simple idea to measure the force that is applied from a VFG, I just have not had time to do anything with it yet. I am deployed for the rest of the month, but maybe I can get someone to do some tests and see what sort of force we are looking at. Thanks for the positive feedback!

POF-USA
06-08-06, 23:20
Frank,
Instead of vertically mounting the upper, which changes the the setup, and any gravity effects (even if minimal). Why not use a pully? Tie a cord to the VFG run it over a pully then tie the weights to the cord.

This is the idea (excuse the crude graphics):
http://groups.msn.com/_Secure/0VgDdArcb5NQPiuTteEXLAg96LymonNzhQK5MAa78OTabvDhy52S!9DXUy5BtWRO!W!IEqnTAyVFuhhJyCnuYSlxiy969J1Hyau05y2AdjFY4lcVQvAcbUJGOglcQWyZM/Test%20Proposal.jpg?dc=4675575950455389026


Your drawing looks great, and I'm sure it will work. I would be nice to determine the amount of weight/force a operator puts on the vertical grip when pulling back during use, and match that weight/force for your test. This type of leverage may induce flex in the upper. Your test would show if this is a issue or not.

I would continue to test as you have been. Take measurements when cold for a base, then take measurements at different temperatures to see how much movement/flex the upper indicates with heat.
Best regards,

Frank
POF-USA

Boom
06-09-06, 11:08
After thinking about this last night, I would love to see what pressure a bipod puts on FF system from a prone position. I'm ASSuming it's along the same lines of a foregrip. But maybe it would be less as the rifle is in a rest position. What do you guys think?

K.L. Davis
06-09-06, 11:53
After thinking about this last night, I would love to see what pressure a bipod puts on FF system from a prone position. I'm ASSuming it's along the same lines of a foregrip. But maybe it would be less as the rifle is in a rest position. What do you guys think?

I thought about this, but never gave it a lot of worry I guess... I may be guilty of personal habit making me not look into it much though. I am an advocate of the bipod being located pretty far back on the weapon, largely so you dont have to make all sorts of movement to reach out and fiddle with it. At times, I will set the left leg short and hold the bottom of it with my offhand, this is a great way to level the rifle quickly.

Anyway, that position probably puts little strain on the weapon, as the "pivot" is so close to the barrel nut, but this is a something to look into for sure.

Most will be surprised by the amount of force that can be put on the rifle from a VFG -- keeping in mind that we are talking about an 18 year old guy that just finished MC basic and is a situation that, as we like to say, makes him water tight... pucker factor you know!

Boom
06-09-06, 12:41
I thought about this, but never gave it a lot of worry I guess... I may be guilty of personal habit making me not look into it much though. I am an advocate of the bipod being located pretty far back on the weapon, largely so you dont have to make all sorts of movement to reach out and fiddle with it. At times, I will set the left leg short and hold the bottom of it with my offhand, this is a great way to level the rifle quickly.

Anyway, that position probably puts little strain on the weapon, as the "pivot" is so close to the barrel nut, but this is a something to look into for sure.

Most will be surprised by the amount of force that can be put on the rifle from a VFG -- keeping in mind that we are talking about an 18 year old guy that just finished MC basic and is a situation that, as we like to say, makes him water tight... pucker factor you know!


I never thought of that. Your right the pucker factor will really put some stress on the forearm.

I'm sure the bipod puts almost nothing on it compared to the above. But I like mine way out front. I've noticed that it does change the POI over the POA if I lean far into the stock. I'm a big guy at 260lbs. I use the harris so it likes to jump around/slide back a little.

Stickman
06-10-06, 11:13
The difference between adrenalin induced combat strength, and shooting on a bipod would make it apples and oranges. I don't doubt that POA/POI shifts are consistant with what you are saying, but I don't think it would be anywhere near the degree of stress on the same parts.

I can't help but wonder if the answer to this is going to be a redesigned receiver with support ribs in additional areas. I think the problem in that regard becomes getting the military to make the change (less than likely). The more realistic answer may be in the upcoming requirements for military rails.

Are there any stats available to show number fo failures in use?

Lumpy196
06-11-06, 20:46
Interesting conclusions on the KAC RIS. So much for the "sucks completely" theory Ive seen thrown around lately.

Boom
06-12-06, 10:15
The difference between adrenalin induced combat strength, and shooting on a bipod would make it apples and oranges. I don't doubt that POA/POI shifts are consistant with what you are saying, but I don't think it would be anywhere near the degree of stress on the same parts.

I can't help but wonder if the answer to this is going to be a redesigned receiver with support ribs in additional areas. I think the problem in that regard becomes getting the military to make the change (less than likely). The more realistic answer may be in the upcoming requirements for military rails.

Are there any stats available to show number fo failures in use?

Stick I agree with you. The amount of stress that can be applied with a forearm is greater then a bipod.

Forest
06-12-06, 13:16
After thinking about this last night, I would love to see what pressure a bipod puts on FF system from a prone position. I'm ASSuming it's along the same lines of a foregrip. But maybe it would be less as the rifle is in a rest position. What do you guys think?

The force the bipod applies is going to be different. It's going to more of an 'up force' rather than a back or a downforce.

While the bipod doesn't push 'up'. It is going to be static and the weight of the receiver is going to be pushing down on it. The end results is it will look like an 'up' force at the point the bipod is attached.

Boom
06-12-06, 17:35
The force the bipod applies is going to be different. It's going to more of an 'up force' rather than a back or a downforce.

While the bipod doesn't push 'up'. It is going to be static and the weight of the receiver is going to be pushing down on it. The end results is it will look like an 'up' force at the point the bipod is attached.

Thats correct Forest. I failed to mention the barrel is a .625 barrel. I tend to pull the stock in tight then lean into the gun. This applies upward force on the bipod/FF rail and tends to drop the barrel a slight amount. Currently I'm changing that barrel out for a stainless heavy 1/8. I hope this will resolve the problem completely.

POF-USA
06-13-06, 01:46
Here is the rest... work continues on this, see the comments at the bottom.

------------------------------------
Test Two -- This was a duplication of the first test, this time with the upper receiver supported by "pinning" into a fixture that represents a lower receiver.

Conventional (non-supported) Receiver
http://img495.imageshack.us/img495/7978/pcdv0062small8bs.jpg

Findings - Here we see an increase in all of the measurments, with a noticable increase in the deflection of the chamber gauge -- further indication that the flexing of the front of the receiver is valid and demonstrable... but are the measurements enough to support a real concern?
http://img154.imageshack.us/img154/6749/testtwo7bu.jpg

------------------------------------
Test Three -- Leaving everything in place and under load from Test Two, I used a small torch to apply heat the barrel nut/chamber area of the upper receiver assembly. Lightly feathering only the chamber area with the torch, I took the temperature to 200 - 220 deg (F) -- not at all an unrealistic temperture for the rifle. The results here were very interesting, the dial gauges reacted immediately to the heat. As this was still an elastic state for the metal, it was interesting to watch as the upper cooled... the measurements returned to the original readings of Test One as the receiver returned to room temperature.

This test (I believe) induced enough alignment error to believe that not only the reliability, but the structural integrity of the weapon may have been compromised.
http://img230.imageshack.us/img230/1976/testthree2kz.jpg

------------------------------------
More Theory -- I had fully expected to see the results that I had seen up to now... I suspect that the defining moment of this problem was actually the removal of the carry handle. The time frame for the apparent increase in some of the issues attributed to the "receiver flexing" does seem to fall in line with the increase in flat top uppers being available. While perhaps not designed that way, the handle is a integral arch that ties the front of the receiver to the rear anchor point (take down pin) and we sill see, adds a LOT of rigitity to the upper receiver.

------------------------------------
Test Four -- An A2/Carry handle upper is built with the same parts as the flat top and pinned in the same fixture. I went straight to the twenty pound test with this...

http://img226.imageshack.us/img226/9895/pcdv0089small3ly.jpg

Findings - The carry handle appears to stiffen the upper receiver a great deal, the deflection at the chamber cauge was actually just over one-onethousandths of an inch!
http://img507.imageshack.us/img507/3088/testfour2rb.jpg


------------------------------------
Test Five -- The next test was with a "piggy back" type mounting handguard... for this test I used a CAS-V system from Vltor on a CMT/Stag M4 style upper -- again, I went straight to 20 pounds on the test.

http://img369.imageshack.us/img369/7735/pcdv0104small8pi.jpg

Findings - Although there was a lot of flex in the handguard, note the chamber gauge deflection was very close to the A2 Carry Handle upper at just slight less than 1.5 thousandths of an inch!
http://img234.imageshack.us/img234/2633/testfive7es.jpg

------------------------------------
Test Six -- Of course the test would not be complete without a look at the new monolithic upper receivers... I only had one such part in my hands during the test, but decided to see how it does.

http://img228.imageshack.us/img228/2714/pcdv0096small3fp.jpg

Findings -- I am going to hold off of specific measurements right now, as the unit I have is a prototype and I am told the production piece will be slighty different... I also hope to compare other entries in the monolitic catagory in a side-by-side match up.

To be fare to everyone though, I will say that both readings were better than those recorded under the twenty pound load on the fully supported receiver in Test One.

I can say that it is very rigid... the monlitic design appears to offer a far more rigid handguard section than is avaiable from any of the above combinations and the measurable receiver flexing is far less than what was noticed from the current flat top upper and barrel nut mounted hand guard systems.

update: the readings for the prototype VIS were handguard deflection of 0.011 and chamber gauge was 0.004

------------------------------------
Test Seven -- A test of a new issue KAC RIS system was interesting...

http://img446.imageshack.us/img446/2536/cimg0527small3oe.jpg

Findings - The RIS did very well really, this is mostly for comparison, but the handguard deflection was 0.0014 and the chamber gauge deflection was 0.007 -- this is about as good as the fully supported receiver in Test One and better than the unsupported receiver in Test Two.

------------------------------------
Conclusions -- This is not the end of the testing... but offers some pretty telling evidence. As stated, I hope to do more side-by-side testing with the monlithics in the near future, as well as some range time with different designs (I have designed a jig that will intentionally stress the upper receivers and see if I can not get them to break!) -- but for now, I feel comfortable with the folowing.

The upper receiver "flexing" issue seems to be real... I believe that the removal of the carry handle does make the platform subceptable to "bowing" the upper enough that it could effect the reliability or integrity of the weapon.

Granted, this will vary from rifle to rifle and is something that most likely would only be experiencd by a shooter that is a very stressful situation and has fired the gun to the point of being quite hot... but this seems like the absolute worst time for it to happen. This flexing also seems to only be an issue on guns that use a barrel nut mounted handguard system.

All of this is most likely a non-issue for 99.9% of the people reading this... The likelyhood that the combination of the weapon configuration, individual user and appropriate situation will all come together exists almost solely on the battlefield... and even there is would have to be the exception rather than the rule -- but, if you prepare for the worst, it is not as much of a surprise when it happens.

Some other notes:

The strongest upper is the old A1/A2 carry handle upper -- I did not test a removable carry handle or one piece optic mount as a possible "bridge" on purpose... as I felt that even if it did stiffen the upper receiver, it would only be as good as its current mounting and can not be relied on as a remedy.

The carry handle also seems to serve well as a heat sink... more on that in the future perhaps.

Yes, there is someone already working on a receiver that uses an itegral optics platform to strengthen the upper... as well as a few lesser known things already out there.

The "piggy back" style handguards do not stress the barrel nut, while it is debatable if they actually provide an additional rigidity to the top spine of the upper receiver, the example used in this testing did not seem to flex the upper receiver. These systems however, do seem to have as much or more rail flex than the current barrel nut mounting designs.

02MAR06 - No doubt that the missing carry handle weakens the receiver... some model work indicates that the "sidewalls" of the upper receiver provide little reinforcement -- the starboard side is a washout with the ejection port taking a large piece of the structure away and it seems that the weak spot on the port side is just below the cut for the cam pin to clear. Most likely the sides are bowing out under load (in the area indicated in the pisture) and the only real support is the top section of the receiver, which allows the front section to flex as it pivots on the front takedown pin.

http://img492.imageshack.us/img492/9582/receiver6zr.jpg

07JUN06 - Finally get to put this back where people can see it! Computer models confirm the idea that the receiver is bending just behind the front lug under load. Some idea for a reinforced receiver are being looked at. I will keep this updated as I get new stuff.

K.L. Davies,

A closer look of your report shows the Cav-V and the Carry Handle upper had the least amount of indicated movement of the chamber .0015.
Did you find why the Cav-V had less indicated chamber movement /receiver flex? It would be great to hear your findings on this.

Have you conducted a test with a vertical grip, and test with heat?
I think this is the test you will find the most movement, compared to the hanging weight. Having a vertical grip mounted by the muzzle will introduce alot of LEVERAGE, when the vertical grip is pulled back toward the receiver during use. I' would think you will see the most indicated chamber movement / receiver flex, when conducting this test compared to the hanging weight test.

The test results showing the RIS rail moving .0014", with weight. I would assume this is due to the front on the rail is supported by the barrel and is not a free float rail system like the others tested. The indicated chamber reading / receiver flex showed a reading of .007.
Keep up the great work. I look forward to more updates. :)
Best regards,

Frank

POF-USA
06-18-06, 10:24
K.L. Davies,

Have you done any testing with the vertical pistol grip yet?
Looking forward to your test results.
Best regards,

Frank
POF-USA

K.L. Davis
06-30-06, 13:02
K.L. Davies,

Have you done any testing with the vertical pistol grip yet?
Looking forward to your test results.
Best regards,

Frank
POF-USA

Yes... I just got back from a short deployment and I am turning around and heading out again soon, but there is some new information that needs sorted through and posted.

The VFG puts much more stress on the upper receiver than a rifle that does not use one -- the reason is that without the VFG, the stress created is limited to that the operator puts on it by "pulling" the barrel down (or off axis in some direction)... this is not really that much, as it is not a good shooting technique.

The VFG however, promotes grip strength and seating the rifle by pulling back on the grip -- all of this force is transered to a leveraging force on the front of the rifle, due to the VFG acting as a lever, perpendicular to the axis of the rifle.

I will get some more stuff up as I get time, this next month is sorta busy for me, but I will get what I can....

Rmplstlskn
06-30-06, 23:11
Your doing an EXCELLENT job with the tests K.L.!

Some of the best AR PHYSICS education I have had in a long time...

Rmpl :D

POF-USA
07-01-06, 00:32
Yes... I just got back from a short deployment and I am turning around and heading out again soon, but there is some new information that needs sorted through and posted.

The VFG puts much more stress on the upper receiver than a rifle that does not use one -- the reason is that without the VFG, the stress created is limited to that the operator puts on it by "pulling" the barrel down (or off axis in some direction)... this is not really that much, as it is not a good shooting technique.

The VFG however, promotes grip strength and seating the rifle by pulling back on the grip -- all of this force is transered to a leveraging force on the front of the rifle, due to the VFG acting as a lever, perpendicular to the axis of the rifle.

I will get some more stuff up as I get time, this next month is sorta busy for me, but I will get what I can....

Thanks for the reply.
I agree with you that the VFG puts more stress (leverage) on the weapon system. Your testing will prove if this is true. I believe we will see more movement with the VFG and heat in regards to the receiver flex.

Come home safe, and keep up the great work.
Best regards,

Frank
Patriot Ordnance Factory (http://www.POF-USA.com)

twl
07-01-06, 09:20
It appears to me that your chamber gauge is being measured about 7" behind the bolt lockup area.

The length of this rod adds a significant increase to the measured movement, due to the angular calculation making a larger measurement, the longer the rod is(further from the chamber).

As a result, the actual movement at the lockup area, is far less than the measurement being taken at the end of the rod behind the back of the upper receiver, because of the length of the rod, and its greater movement in the arc at the end, than at the actual area of concern.

I think that this needs to be taken into account, and measurements taken at the bolt lockup area, by inserting the dial-indicator thru the ejection port.
That is, if we are looking at this phenomenon as being a potential cause of misalignment during bolt unlock, possibly causing excessive and uneven bolt wear, or breakage.

The actual movement at the chamber or lockup area will be about 1/7th of what is being measured at the end of the rod, due to the angular increase in where the measurement is being taken. It is quite possible that this much smaller movement may easily be taken up in the play available at the gas rings, which allow some small "wiggle" movements of the bolt inside the carrier.

If we are looking to determine a possibility of carrier binding on the upper receiver after unlock(because of this flex), then we must measure the difference in the receiver carrier channel from the front of the ejection port, to the rear of the receiver, to determine a "binding point", and determine if this is beyond the clearances allowed for movement of the carrier in the channel. If we have a "bind-point", just sliding the carrier back and forth in the channel, should allow you to feel if it is actually a problem to consider.

My "gut feeling" here is that any of this flexing going on can be accomodated by the play in the gas rings, and in the clearances allowed around the carrier, in most of these cases seen here.
Perhaps it may cause some uneven wearing to a certain extent, if the gun is always fired with this kind of pressure on the ends of the handguards. However, I think that in general use with heavy pressure exerted only in some of the circumstances the weapon will see, it may/may-not even be a concern.

Regarding, this worsening when heated, it is known that aluminum has a different expansion rate then steel, and the aluminum receiver-hole holding the barrel extension will enlarge(loosen up) to some extent when hot, thus possibly(likely) causing the phenomenon of worsening this deflection measurement when hot.

Just my thoughts.

POF-USA
07-01-06, 19:44
K.L.Davis test are to determine flex in the receiver.
His results have shown some interesting results.
The amount of flex on a receiver with hanging 20 lbs on the rail system,
then adding heat showed flat top receiver flex / movement as much as .016".
Adding heat to the testing helps to test as if the weapon system is operating.
It will be interesting to see the results with the use of a vertical grip.

His test results show that a carry handle upper has less flex / movement of the receiver when hanging weight. The carry handle upper only flexed / moved .0015". I beleive this is because the bridge support of the carrying handle. I hope his test results will help to prove why.

What's another interesting point of his test in his very rigid looking fixture. His fixture looks to be stronger then any lower receiver I could think of.
I would have to assume his fixture would help to reduce flex / movement of the upper receiver during his testing, compared to using a standard lower receiver.
Keep up the great work K.L. Davis. Your test result could help to improve product designs. :)
Best regards,

Frank
POF-USA

K.L. Davis
07-01-06, 21:13
It appears to me that your chamber gauge is being measured about 7" behind the bolt lockup area.

The length of this rod adds a significant increase to the measured movement, due to the angular calculation making a larger measurement, the longer the rod is(further from the chamber).

As a result, the actual movement at the lockup area, is far less than the measurement being taken at the end of the rod behind the back of the upper receiver, because of the length of the rod, and its greater movement in the arc at the end, than at the actual area of concern.

I think that this needs to be taken into account, and measurements taken at the bolt lockup area, by inserting the dial-indicator thru the ejection port.
That is, if we are looking at this phenomenon as being a potential cause of misalignment during bolt unlock, possibly causing excessive and uneven bolt wear, or breakage.

The actual movement at the chamber or lockup area will be about 1/7th of what is being measured at the end of the rod,
Yep, the measurements are taken about 7" back... compensating for this is simple math however, it could be any distance from the chamber and all that needs to be done are the numbers adjusted to consider that distance -- of course at some point, there would be enough flex in the "gauge" to become a concern, but it was not with this setup. The offset of the extreme edge of the bolt face is actually less than 1/7 of the gauge reading... iirc it was a factor of 0.06 of the gauge reading.

Keep in mind also that this measurement is stacked... you will see that there *should* be an equal movement in the opposite direction, 180 degrees from the extreme movement in one direction, but obviously there can not be.

If you think of it as a teeter-totter, it is like this... say that the gauge shows there should be a 0.001 inch movement (in relation to the bolt face and the barrel extension) and this movement is constructed to be in the direction of the muzzle -- naturally, there should be a 0.001 inch movement at a point directly opposite of this, towards the rear of the rifle -- but, in this case, on end of the teeter-totter is resting on the ground and can not move, so you force the fulcrum point to move forward the distance of the gauge measurement and the acutualy measured movement of the bolt face (agian, in relation to the barrel extension) is in fact 0.002, making up for the equal and opposite movement that could not occur.


due to the angular increase in where the measurement is being taken. It is quite possible that this much smaller movement may easily be taken up in the play available at the gas rings, which allow some small "wiggle" movements of the bolt inside the carrier.

If we are looking to determine a possibility of carrier binding on the upper receiver after unlock(because of this flex), then we must measure the difference in the receiver carrier channel from the front of the ejection port, to the rear of the receiver, to determine a "binding point", and determine if this is beyond the clearances allowed for movement of the carrier in the channel. If we have a "bind-point", just sliding the carrier back and forth in the channel, should allow you to feel if it is actually a problem to consider.

My "gut feeling" here is that any of this flexing going on can be accomodated by the play in the gas rings, and in the clearances allowed around the carrier, in most of these cases seen here.
Not really sure how the gas rings would have anything to do with this... the bolt bearing surfaces are forward and aft of the gas rings and there *should* be no lateral load on them at all -- if everything is made right anyway.

Also, as I am sure you know, there is not any real "play" in the bolt... sure, setting on the bench there is some slop around the bolt in the receiver bore, but the rifle is designed to use the top cartridge in the magazine as a bearing surface -- this in fact forces the bolt "up" into the top of the receiver bore and there is no slop or play... granted, the spring pressure and mass of the bolt assy could be overcome, but keeping in mind that work is a product of force and time, I do not think there is emough of the later to really give this a lot of concern.



Perhaps it may cause some uneven wearing to a certain extent, if the gun is always fired with this kind of pressure on the ends of the handguards. However, I think that in general use with heavy pressure exerted only in some of the circumstances the weapon will see, it may/may-not even be a concern.

Regarding, this worsening when heated, it is known that aluminum has a different expansion rate then steel, and the aluminum receiver-hole holding the barrel extension will enlarge(loosen up) to some extent when hot, thus possibly(likely) causing the phenomenon of worsening this deflection measurement when hot.

Just my thoughts.

The rule of thumb is that Al expands at a ratio six times that of tool steel... but given the design of the barrel mount and the fact that the barrel nut (should be) is steel, this is a non concern.

Under heat, there have been measurements at the gauge that would reflect a combined "gap" of 0.003 at one side of the bolt locking lugs -- does this mean it is a cause of failure? Not sure, but it is enough to at least give consideration.

The purpose of the test (originally) was to examine the theory that the barrel does or does not flex in the receiver under load/heat -- you know there was a lot of speculation and jabber about the idea (both for and against), so I just wanted to sit down and present some sort of repeatable test that shows if the idea is in fact sound, or garbage...

Given that more than one manufacturer is working to strengthen the missing "bridge" of the flat top uppers, it seems that the presentation was of at least some value.

twl
07-01-06, 21:55
Interesting.

I really appreciate your detailed response, and your addressing my points individually.
That was really nice.
I'm glad that my comments didn't offend, because I intended them to be as helpful as possible, from the way I was reading the procedure.

Always interested in seeing what improvements can be made, and how they will affect things.

Heavy Metal
07-04-06, 16:27
The force the bipod applies is going to be different. It's going to more of an 'up force' rather than a back or a downforce.

While the bipod doesn't push 'up'. It is going to be static and the weight of the receiver is going to be pushing down on it. The end results is it will look like an 'up' force at the point the bipod is attached.

Right Forrest, you are introducing tensile forces on the upper with a bipod and compressive forces with stress on the handguard.

K.L. Davis
07-06-06, 23:58
Interesting.

I really appreciate your detailed response, and your addressing my points individually.
That was really nice.
I'm glad that my comments didn't offend, because I intended them to be as helpful as possible, from the way I was reading the procedure.

Always interested in seeing what improvements can be made, and how they will affect things.

No problem... I hope my pseudotechobabble (tm) was understandable?

BTW: no offense taken at all... in fact, most can rest in the comfort that I am perhaps too dull to realize when someone is trying to offend me.

UPSguy
09-25-06, 12:25
any new updates to this testing?

K.L. Davis
09-25-06, 13:25
any new updates to this testing?

Not as of yet... sorry. I have been so two-blocked lately that I have had little opportunity to finish the couple of other posts that I have working on here -- trust me though, I am working on things still.

Between Truth, Justice, The American Way, influencing young minds and damaging young bodies, getting ASOSA back on line, a dog that has had more surgeries than Cher and wordsmithing my retirement letter!!!!!!

...some things get back shelved for the time being.


I think the jist of the testing is there though, flat top receivers do flex. There is some more info that I will try to get posted, but I set out only to answer once and for all an argument that was going on in the development field. I think it was answered.

I am sure that I can get a MUR to test... Hopefully this will give a good idea of how the "beefier" uppers hold up, but the bottom line is that A2 and Monolithic uppers are the champs as far as strength goes.

Ned Christiansen
09-28-06, 16:26
Blimey!

I just don't quite know what to say here.

KL, your testing is over the top. Just the kind of thing I love to see, but to be honest, although I'm sure it happens in the firearms industry, it is not often shared with Joe AR-head as you have done..... thank you for your work and for sharing it.

K.L. Davis
09-30-06, 21:07
Over the last few days, I have had several folks ask if there was going to be more receiver testing done... so, hell, why not?

I have started to ask around for new stuff to test -- so far I have shaken the trees to see if I can get a MUR and production VIS... as well as the new billet upper from LaRue Tactical -- so it looks like this is shaping up to be a test of the "improved" designs that are out there.

Great stuff, and I am looking forward to seeing what improvements have been made... I am sure that everyone will be pleased with the efforts from the industry and hope that more good things are still upstream.

If anyone can think of another entry that should be tested... feel free to add on your comments and ideas. I would like to round up a billet upper from Oberland Arms and a couple others come to mind -- but let's see what the forum is thinking!

UPDATE: Well, an Oberland Arms upper is in the test... thanks to a generous donor :cool:

KLD

jmart
09-30-06, 22:51
Over the last few days, I have had several folks ask if there was going to be more receiver testing done... so, hell, why not?

I have started to ask around for new stuff to test -- so far I have shaken the trees to see if I can get a MUR and production VIS... as well as the new billet upper from LaRue Tactical -- so it looks like this is shaping up to be a test of the "improved" designs that are out there.

Great stuff, and I am looking forward to seeing what improvements have been made... I am sure that everyone will be pleased with the efforts from the industry and hope that more good things are still upstream.

If anyone can think of another entry that should be tested... feel free to add on your comments and ideas. I would like to round up a billet upper from Oberland Arms and a couple others come to mind -- but let's see what the forum is thinking!

UPDATE: Well, an Oberland Arms upper is in the test... thanks to a generous donor :cool:

KLD

I've followed this topic since the beginning and find it pretty fascinating. Along the course of your testing, have you been able to correlate the amount of flexing with either reliability or accuracy degradation?

bigbore
10-01-06, 07:03
< shouting Brit accent >
I'd like to see......
< / shouting Brit accent >

A MUR w/DD Lite rail next to a the LaRue receiver w/LaRue rail.

I wonder if the mounting system of the DD makes any difference.


I wish there was a way to apply any of this testing to actual effects on functional firing weapon; what difference does any of it really make?

With my yellow glasses - I see folks who must be putting much more than 20lbs on the end of a fifle length float tube. Standard receivers, loads loaded as hot as possible, and I cant think of a problem ever being had.

I would have to imagine a yellow glass shooter slung up prone, is puttin way more stress on a tube than any soldier with a carbine, even under stress.

This testing is neat, but in what way does any of it apply to anything a simpleton like myself can relate to?


It would be cool if you could do your testing with hot uppers, or mount something like a laser level on the receiver and a aiming point on the front sight of a match rifle to see how much its flexing from a sling.

jmart
10-01-06, 09:46
I wish there was a way to apply any of this testing to actual effects on functional firing weapon; what difference does any of it really make?

With my yellow glasses - I see folks who must be putting much more than 20lbs on the end of a fifle length float tube. Standard receivers, loads loaded as hot as possible, and I cant think of a problem ever being had.

I would have to imagine a yellow glass shooter slung up prone, is puttin way more stress on a tube than any soldier with a carbine, even under stress.



I asked myself that very same question when I started reading this thread, but the more I thought about it, it seemed the tension a sling would place would be more of a compression than a bend. The bulk of the force's vector is coming back along the axis of the tube (down the sling and toward the shooter's bicep), comparatively little is going downward.

I do share your same curiosity though about how much flex needs to occur before reliability and/or accuracy detriorates. Between this thread and the "migraine inducer" Larue billet receiver thread over at you know where, it would be neat to figure out between the two what the correlation is between flex/dimensional errors and accuracy/unreliability.

Nitrox
10-01-06, 10:05
I'd like to see a high rise upper added to the test. DPMS has made them over the years but it looks like RRA is the only game now.

K.L. Davis
10-01-06, 13:33
Okay... as of last night, I have an Oberland Arms receiver.

This morning I got word that a production VIS and MUR are on deck as well. I have not heard from LT... probably not back in the shop until monday.

I will hit up DPMS and RRA to see what they want to submit, and I have a couple of emails that may possibly bring in a couple of others. I will see if DD wants to send a new handguard to test the mounting method... but it would have to be ran against a "traditional" mounted free float on the same upper -- running the test on two different manufacturers introduces a variable.

So... the reason I started this testing a couple of years ago was just to see if there was flexing in the upper receiver -- the camps where split and you either thought there was, or thought there was not. I like to think that this testing put that to bed... and most manufacturers and end user organizations that I talk to now, subscribe to the results of the test.

I don't have any direct correlation to the amount of flex v. mechanical problem... but I do know that some of the shops that have replicated or continued the tests claim that it is at least a factor in bolt breakage -- anything that I can add to this is purely anecdotal. I am also told that when the test is taken to 400 degrees, the flex is very severe!

We all know from our days in basic training, that the traditional sling to the FSB can flex the barrel enough to move POI... but the test here was to see if loading the handguard caused the front of the receiver (and therefore the relation to chamber/bolt) to flex -- interestingly, but easy to understand, is that the problem is manifest under "up and down" loads and not nearly as noticable under any sort of "side to side" load.

I would say this... cutting off the carry handle reduced the structural integrity of the upper, no doubt about it -- does it matter though? This is just me thinking, but we have had a really bass ackwards approach to this for a long time -- think about how much you would be willing to pay for a good bolt action receiver? The upper receiver is functionally the same thing, but if someome was selling $35.00 flat tops on "The EE", they would fly off the shelf (if they had M4 cuts) -- and in spite of that, we are willing to pay $200.00 for a lower. Hey, if the hammer pins holes are straight, the mag well in spec and the receiver extension lines up -- that is all we can expect from the lower... I guess because it is the serial numbered part and carries "The Name", we throw the extra cash at it?

Again, I am not going to replace every flat top receiver just because it may flex or whatever, but if I had a choice for a new build -- that was going to be used in the defense of life... I would opt for the best upper I could get my hands on.

Which one is that? Hopefully, in a couple of weeks, you can make that decision based on what you read here.

bigbore
10-01-06, 14:18
We all know from our days in basic training, that the traditional sling to the FSB can flex the barrel enough to move POI... but the test here was to see if loading the handguard caused the front of the receiver (and therefore the relation to chamber/bolt) to flex -- interestingly, but easy to understand, is that the problem is manifest under "up and down" loads and not nearly as noticable under any sort of "side to side" load.


I was talking about NM Service Rifles with the sling attached to the float tube. There are some big guys putting a LOT of pressure on those tubes - even though its not forced directly down, things are still bending. Same can be said for the match uppers with float tubes built an flat top uppers. Amount of flex as temps increase - these guys arent shooting more than 10 rounds at a time. Seeing scores shot with ARs - I dont for a minute believe the flexing alone has any noticable effect on accuracy.




think about how much you would be willing to pay for a good bolt action receiver? The upper receiver is functionally the same thing,


Apples and oranges of a comparison for this testing. It would be nice to compare the consistancy of the internal spec dimensions of receivers. A nice black (so it matches the lower) upper with M4 feedramps, for $35, that the barrel extension fits in like a hot dog in a garbage can, and bolt carrier that rotates around when closed is another thing...

But yes, they would sell because the folks buying them dont shoot more than 50rds a year off a bench at paper plates 50yds away;)




Again, I am not going to replace every flat top receiver just because it may flex or whatever, but if I had a choice for a new build -- that was going to be used in the defense of life... I would opt for the best upper I could get my hands on.


Is the best the enemy of good enough? What will you use to determine what is "the best"? How many of each can be tested to find who is more consistant?

I would hope this will break down as best, good enough, and decoration.

Best - I would determine by strength, and consistancy of "spec".
I would expect the "billet" pieces to come out as the best.

Good Enough - I would think Colt, and CMT - because of consistancy to specs.

Decoration - the gunshow specials where all the pieces fit with "room to spare".

Nitrox
10-01-06, 16:01
Best = Value

Value = Need/Cost

Need, and Cost can be rated 1 - 10, 10 being highest.

Submariner
10-01-06, 16:32
Is the best the enemy of good enough? What will you use to determine what is "the best"? How many of each can be tested to find who is more consistant?

I would hope this will break down as best, good enough, and decoration.

Best - I would determine by strength, and consistancy of "spec".
I would expect the "billet" pieces to come out as the best.

Good Enough - I would think Colt, and CMT - because of consistancy to specs.


After seeing newer and "better" gear in five years of classes and staying current with the boards, I came to much the same conclusion; " Is the best the enemy of good enough?"

The kind of testing that would be required to determine the "best" would add significantly to the cost of these parts. (Imagine two identical valves, one certified for use in a nuclear power primary system and another for a drain line on a surface ship; the former costs 2 to 5 times the latter, perhaps more.)

I cannot afford perfection in this arms race. Colt lowers, even the lowly Sporter I's, with uppers made from Colt barrels, Colt upper receivers, and Colt bolt carrier groups "work pretty good". At this point, money spent on ammunition for training and practice is arguably better used.

Resq47
10-01-06, 17:01
Agreed, Sub. If I find myself going cyclic on the bigger, better, faster loop I go back to Kamm's law of diminishing returns. The difference between having an AR that runs and not having one at all is much larger than the little hoo-haws we deliberate on for waaaay too long.

That said, it's enlightening to see technical comparisons being done even if it's essentially esoteric.

K.L. Davis
10-01-06, 17:40
To clarify... I hope to find the design variation that provides the most strength -- as for which is "best" that is ultimately up to the end user.

Steve, you know that you and I are both very pragmatic when it comes to this stuff... hell, I don't have nearly half of the high zoot stuff that is out there on my personal guns. But we have both seen the strange alignment of priorities that a lot of the end users subscribe to -- granted, a lot of them only shoot 50 rounds a year and the closest they will ever get to their gun being in "battle", is if it falls over in the closet and scratches their wife's favorite high heels.

But, it used to be barrels... remember how folks would say "I want this name brand lower; with a custom plated NM bolt; a 200 dollar stock and another 200 bucks worth of extra grips; three lights; 4.7 yards of rail on a 300 dollar fore end; at least three sighting options, one of which is optic and cost more than the rifle itself; I'll need a 100 dollar flash suppresor; a sling that comes with a video of how to use it... oh, and what is the cheapest barrel you have?"

Now, in some sort of knee-jerk reaction I guess, one can not show up on the range without a gun that has the latest ubertube...

That said, I am not sure that any of the crop of new uppers are any better... yet.

For those that don't know me... When I first really started into the gun thing, IPSC was a budding sport and the number of custom 1911 builders could be counted on one hand... the "martial artist" and the "roonies" were just starting to go their seperate ways and for most guys, extended safeties, beaver tails, better sights and a trigger job was about as exotic as you could get -- there was, however, a group that was putting weights on the end of the barrel... they even ported the weights and played around with cartridges once thought extinct, this small group of guys mounted over sized goodies on their guns and welded/filed/milled in different shapes... it really was an interesting time.

I worked part time as a gun plumber for a small shop in Phoenix then, the Hassayampa River Shooters and the Cactus Match League would meet in the evenings and we would have a great time... a few would sit on the picnic tables and preach the ways of our particular following, and young shooters would sit wide eyed and soak it in. I was doing pretty good with "custom" pistol building at the time... well beyond just sights and trigger work, I had ventured into welding up and fitting barrels, extractor tuning, lug cutting and ramping and releaving -- truley state of the art 'smithing.

Then, one night as I was sitting on the tailgate and discussing the virtues of my wares... a kid that had shot earlier that night (and not very well mind you) walked over and said "I have $200.00 to spend"... he held out his mostly stock AO 45 and asked "How do you recommend I spend it?" -- well. I answered honestly and pointed him to a guy that worked for Phoenix Arms and said "Go buy 200 bucks worth of his reloads and practice more"... you know that Charlie Brown whaa, whaa, whaa sound? I swear you could actually hear that after I told him this.

The next week, I did not have nearly the following of new shooters hanging around seeking wisdom... it seems that my suggestion, while it no doubt would have improved his shooting, did little to improve his appearance on the line... I learned a lot that night, but I have not changed. If something truley offers advantages that offset the price, I will wholeheartedly recomend that item... if, however, something is "fluff" or simply bragging rights, you won't find it in my favor. Therefore, I do these sort of tests so that I can make sound recommendations based on what I know to be facts.

In honor of a good friend recently lost... the first Rule of Gunfighting is: Have a gun.

That simple axiom speaks volumes.

K.L. Davis
10-03-06, 20:04
Update...

The test should go down soon, I have two short deployments this month, but can probably find time between them to get it all taken care of.

I have commitments for product from:

Daniel Defense
Vltor (New VIS and MUR)
Oberland Arms (private owner)

and I am pretty sure that RRA and DPMS won't shy away.

The testing will include how much strain *can* be applied via a VFG. Should be lots of fun!

Stickman
10-03-06, 21:59
K.L.- Thanks again for keeping this public.

*edit KevinB

Mark LaRue
10-04-06, 09:05
Gentlemen, my comments have now been "edited out of context" by the mods (KevinB). To avoid confusion, I withdrew what they left.

But be advised, I stand solidly behind my original post ... I no longer allow known trolls to freely besmirtch the efforts of myself and my folks here at LaRue Tactical.
www.laruetactical.com

*edit KevinB

K.L. Davis
10-04-06, 16:58
Very sorry you feel that way... one reason that I post not only the findings of the testing, but the specifics of how it was done, is that so anyone can duplicate the testing -- I have nothing to hide or recondite designs, and certainly would not be so open about what is going on, if I was not being forthright about it.

Submariner
10-04-06, 20:35
Does Grant have any? Or just Denny's? Maybe we could take up a collection for the test.

Wonder how long it will be before LaRue only offers their products throught the web site. Now that they are established, it would make good business sense.

K.L. Davis
10-05-06, 09:31
I have word back this morning that DPMS is sending a package of stuff out today... also, I have an email from a private party that says he has a new LT upper on order and will send it out for the test as soon as he gets it.

So... I just wanted to kick this back towards the tracks, before it gets off in the weeds and becomes a bunch of muck raking.

Thors ~ Hammer
10-05-06, 09:42
Keep this on topic.

POF-USA
10-06-06, 00:34
K.l. Davies,

Please Continue Your Test. Your Test Will Help To Improve Product Designs.
I Hope To See The Test With A Verticle Grip Attached To The Rail System, Far From The Receiver With Weight.
This Will Or Will Not Show How Much Flex The Receiver Has Under Pressure With Leverage. Keep Up The Great Work! :)
Best Regards,

Frank
PATRIOT ORDNANCE FACTORY (http://WWW.POF-USA.COM)

Mark LaRue
10-07-06, 14:51
Gentlemen, my comments have now been "edited out of context" by the mods (KevinB). To avoid confusion, I withdrew what they left.

But be advised, I stand solidly behind my original post ... I no longer allow known trolls to freely besmirtch the efforts of myself and my folks here at LaRue Tactical.

M4Guru
10-07-06, 16:18
I just caught this thread, very interesting results. I never guessed the KAC rail would have fared so well, as i experience a some accuracy change anytime I change the dynamics of the setup on my M4.


I plan on doing a lot of flex testing on the new Larue billet upper, using a Larue rail and Noveske barrel. Shooting it at Iraqi insurgents. Larue makes the best stuff out there, and Mark and his crew take care of the end-users in need. Last week I was in dire need of an SPR mount for my team and Mike at Larue had me fixed up so fast I had my scope mounted before I hung the phone up. I personally take any slander of Larue by a competitior as an ultimate show of unprofessionalism.

"They would rather base their image on internet hype, than to work on improving a product."

Mark and his crew's rep is based on real-world usage. There has never been anything asked for by our community that Larue Tactical has refused, citing their products already being good enough. The same cannot be said for others.

K.L. Davis
10-07-06, 17:30
I just caught this thread, very interesting results. I never guessed the KAC rail would have fared so well, as i experience a some accuracy change anytime I change the dynamics of the setup on my M4.


I think the reason the KAC setup shows a lower amount of movement at the gauge, is (I suspect) also the reason that you see a POI change when you change things around on it -- this is the only setup that was tested that shares the load with the barrel.

It is interesting to note the results though... I hope to see from the next batch of testing that there is a movement towards making this piece stronger -- but only time will tell on that.

KevinB
10-07-06, 17:45
I edited a few comments to remove inflamatory comments.

- We understand several people in the industry dislike each other - fine - find a field were everyone gets along and you've found the key to utopia...


Since KL's findings have been open - other members/IP's/Manufaturers are clear to re-create them -- I seriously doubt that he would attempt to do a HipFiredGun on this issue -- but if someone beleive this may not be open or unbiased they are free to do their own.


Lets stay technical and impersonal

Boom
10-07-06, 17:48
I edited a few comments to remove inflamatory comments.

- We understand several people in the industry dislike each other - fine - find a field were everyone gets along and you've found the key to utopia...


Since KL's findings have been open - other members/IP's/Manufaturers are clear to re-create them -- I seriously doubt that he would attempt to do a HipFiredGun on this issue -- but if someone beleive this may not be open or unbiased they are free to do their own.


Lets stay technical and impersonal


Yes Kevin, sorry for creating any problems I'll stay out of this from now on.

jmart
10-07-06, 18:50
Lets stay technical and impersonal

What is the correlation between accuracy and amount of flex? How many MOA will POI shift for each, say, .005" amount of flex?

K.L. Davis
10-07-06, 18:57
Thanks KevinB -- Folks... let's take a deep breath here.

You know those things that we are so sure about, but find out are not true? Like James Dean wore a red windbreaker, not a leather jacket? Or that Rick Blaine (as played by Bogie) never said "Play it again, Sam"?

Something gets started and we hear it enough... it becomes real -- what is real is that I did this testing for one reason and one reason only: To test the (then current) theory that the front of the AR receiver was subject to significant flexing from forces applied to the handguard.

At the time, there were people that thought both for and angainst the idea, it was proposed that the front of the receiver was flexing... I did not see how that was possible, but all of the anecdotal evidence supported that it was. The test revealed that in fact there is a flex, but it is the entire receiver assembly that is flexing and this is attributed to the removal of the permanent carry handle. These test have been redone by others, including some of the firearm manufacturers, and hold valid with everyone that I have talked to. Naturally some of the follow on testing came up with different numbers than I did, but the results are common and support the same findings, time and again.

I like to think that I helped out the entire community with the testing that I did, and will continue with this and other things... I can make the results of the tests available to the manufacturers, or public -- I prefer both, but will not, if all it does is turn into a huge contest that tries to attach motives or supposition to the testing that simply does not exist!

I did not, at any time, preport to say that any one product was substandard or superior to anything, I reported that certain designs (regardless of who makes them) may attribute to the problem -- I used one handguard as much as possible, to remove a possible variable, but it does not matter who made it... all I was concerned about was how it attached and finding out what the real story is... I say case closed on that chapter.

The information is provided so that anyone can take it and use it however they wish -- I know that there are companies that have used it to try to make a better product, but any assumption of what the results mean, other than cold hard matters of fact, are just that: assumptions made by the person(s) making them.

Nitrox
10-07-06, 19:49
I would like to know how much flex is required to prevent a live round (or dummy for testing) from chambering. And, how much flex does it take for a bolt lug to sheer off.

jmart
10-07-06, 20:37
Thanks KevinB -- Folks... let's take a deep breath here.

You know those things that we are so sure about, but find out are not true? Like James Dean wore a red windbreaker, not a leather jacket? Or that Rick Blaine (as played by Bogie) never said "Play it again, Sam"?

Something gets started and we hear it enough... it becomes real -- what is real is that I did this testing for one reason and one reason only: To test the (then current) theory that the front of the AR receiver was subject to significant flexing from forces applied to the handguard.

At the time, there were people that thought both for and angainst the idea, it was proposed that the front of the receiver was flexing... I did not see how that was possible, but all of the anecdotal evidence supported that it was. The test revealed that in fact there is a flex, but it is the entire receiver assembly that is flexing and this is attributed to the removal of the permanent carry handle. These test have been redone by others, including some of the firearm manufacturers, and hold valid with everyone that I have talked to. Naturally some of the follow on testing came up with different numbers than I did, but the results are common and support the same findings, time and again.

I like to think that I helped out the entire community with the testing that I did, and will continue with this and other things... I can make the results of the tests available to the manufacturers, or public -- I prefer both, but will not, if all it does is turn into a huge contest that tries to attach motives or supposition to the testing that simply does not exist!

I did not, at any time, preport to say that any one product was substandard or superior to anything, I reported that certain designs (regardless of who makes them) may attribute to the problem -- I used one handguard as much as possible, to remove a possible variable, but it does not matter who made it... all I was concerned about was how it attached and finding out what the real story is... I say case closed on that chapter.

The information is provided so that anyone can take it and use it however they wish -- I know that there are companies that have used it to try to make a better product, but any assumption of what the results mean, other than cold hard matters of fact, are just that: assumptions made by the person(s) making them.

Fair enough, but until we can reliably and accuractely correlate degree of flex with: (a) degradation in accuracy, (b) degradation in reliability, or (c) reduced service life of components, then it's just interesting data gathered because we can measure something.

I'm not saying the testing has no merit, but by itself, it's just some data points.

NeilsonTactical
10-07-06, 21:09
Interesting conclusions on the KAC RIS. So much for the "sucks completely" theory Ive seen thrown around lately.


I know it.

I own one and like the thing as much as the "new" systems I own.


GREAT thread.

K.L. Davis
10-08-06, 00:53
Fair enough, but until we can reliably and accuractely correlate degree of flex with: (a) degradation in accuracy, (b) degradation in reliability, or (c) reduced service life of components, then it's just interesting data gathered because we can measure something.

I'm not saying the testing has no merit, but by itself, it's just some data points.

You are right on in some parts...

Accuracy is easy to figure, the difference of the angle between the sights and the bore, subtended to range... the second two parts have been looked at by manufacturers and I am told that the test was a welcome source of information by them.

But, you do point out that the original intent of the test was reached... therefore I agree that any further testing under the auspices of the original question is futile... case closed, the testing is conclude here (https://www.m4carbine.net/showthread.php?p=17681#post17681).

edhresko
10-08-06, 12:20
From a purely theoretical point of view, it should be relatively trivial to determine flexure based on the numbers already posted. Torque is Torque and torque generated by a force perpendicular to the axis is the same as torque generated by a VHG...the amount of force required by the VHG will just be different. It's been a few (read: 15) years since I took my engineering statics class, but once I pull out the old books, I'll post a result.

baffle Stack
10-08-06, 13:43
From a purely theoretical point of view, it should be relatively trivial to determine flexure based on the numbers already posted. Torque is Torque and torque generated by a force perpendicular to the axis is the same as torque generated by a VHG...the amount of force required by the VHG will just be different. It's been a few (read: 15) years since I took my engineering statics class, but once I pull out the old books, I'll post a result.

Cool. Post your free body diagram too. I'm taking Statics now and would like to actually apply this boring ass class to something I'm interested in. Like the M4! IM me.

jmart
10-08-06, 14:16
From a purely theoretical point of view, it should be relatively trivial to determine flexure based on the numbers already posted. Torque is Torque and torque generated by a force perpendicular to the axis is the same as torque generated by a VHG...the amount of force required by the VHG will just be different. It's been a few (read: 15) years since I took my engineering statics class, but once I pull out the old books, I'll post a result.

Considering a VFG, how much of the force vector is perpendicular to the HG (deflection/torque) vs how much is along the axis of the fore end (compression)? When I think of a VFG, I think of the user pulling back against it to get the butt solidly positioned in the user's shoulder. Only a small fraction is used to pull down to combat muzzle rise. Same thing with a NM sling on a Service Rifle -- the shooter is looped up and the force of the sling, attached to the upper arm, is primarily pulling the weapon in tight into the user's shoulder. This force is applied more "along axis", in compression, rather than in a perpendicular direction to the handguard.

edhresko
10-08-06, 16:01
Considering a VFG, how much of the force vector is perpendicular to the HG (deflection/torque) vs how much is along the axis of the fore end (compression)? When I think of a VFG, I think of the user pulling back against it to get the butt solidly positioned in the user's shoulder. Only a small fraction is used to pull down to combat muzzle rise. Same thing with a NM sling on a Service Rifle -- the shooter is looped up and the force of the sling, attached to the upper arm, is primarily pulling the weapon in tight into the user's shoulder. This force is applied more "along axis", in compression, rather than in a perpendicular direction to the handguard.

Correct, but the thing to remember is that any weight or pressure (depending on where you're doing the measuring) will generate both a force and a moment. A moment is essentially torque. A moment will be generated for any force that's not in line with the point being measured.

Keep in mind that these calculations are not meant to be something you could design around to determine failure points. It's really more just to get a rough (within 10%) idea of the types of forces on a VFG you'd need to get an amount of flex similar to the experiment KL did.

A few simplifications need to be made to do this in any simple matter, and since it's been years since I've taken calculus, simple = good.

Simplifications:
1) The barrel and handguards are massless. Otherwise, we'd need to weigh them and determine their CG.
2) The barrel and handguards are rigid. While this is obviously not true, taking into account the deformation of the handguards would increase the complexity of the calculations quite a bit, and really would make very little difference. Probably less than 5% difference.

First, to determine the forces and moments, we need to simplify the gun a bit. Since we're measuring from the barrel nut, we can simplify it to a cantilevered beam with the nut fixed and the muzzle hanging out in space.

Now, for the example that KL ran, there will be a moment (i.e. torque) and a shearing force. The shearing force will the same as the weight that was used, since we're considering the assembly massless.

For the torque, M =Force * Distance

so for the 20 lb example,
M = 20 * 7.5" = 150 inch-lbs

So now we want to find out how much force on a VFG will have the same amount of flex. Again, we'll simplify and assume that all the force is pulling back.

I made a few measurements, and my TangoDown VFG is 4.5" from the centerline of the bore. So with a 4.5" moment arm,

M= Force * Distance

150 = Force * 4.5
Force = 150/4.5
Force = 33 1/3 lbs

In general, with a 4.5" VFG, It should take about 1 2/3 times the force parallel to the bore axis.

However, in real life, the person shooting the gun doesn't apply all the force at the end, but closer to the middle or even the top of the VFG. If the pressure was applied all parallel to the bore at 2" down, then the force would be around
75 lbs!

Again, this is a simplification, but I think if KL were to do the experiment, he'd find numbers that were similar (but not exactly equal) to these calculations.

Also, if anyone out there can find a major fault in my logic, I'd like to hear it. I haven't done any static equiliberium calculations in a long, long time...

bigbore
10-08-06, 18:03
seems more posts are being deleted here as often as arfcom. I wait a minute for the page to load only to see its no longer here?

Thors ~ Hammer
10-08-06, 18:07
seems more posts are being deleted here as often as arfcom. I wait a minute for the page to load only to see its no longer here?

Trolling and personal attacks will not be allowed. If that means I delete posts to keep the thread on track well thats whats going to happen.

I'll say it again please keep this on topic.

Nitrox
10-08-06, 18:30
Trolling and personal attacks will not be allowed. If that means I delete posts to keep the thread on track well thats whats going to happen.

I'll say it again please keep this on topic.

If you're deleting off topic posts then why leave all the off topic reminders?

STAFF
10-09-06, 09:22
When posts go off topic with either personal attacks and or innacurate information, we have two options. We can leave the posts as is and then the entire thread as a whole does down hill. The other option is to correct the few posts that are out of line and salvage the discussion as best we can.

We know that people don't like to have their comments removed, but if they stayed on topic and saved the personal attacks for offline, we wouldn't have to do anything.

Other forums suffer from constant bickering, name calling and personal attacks. These things do not add to a technical discussion in any way and is why we do not permit it to happen here.

KevinB
10-09-06, 12:12
I did the edit and cut's -- IF you have issues with this method please PM me and we can discuss this rather than derail a good thread.

K.L. Davis
10-09-06, 12:38
Again, this is a simplification, but I think if KL were to do the experiment, he'd find numbers that were similar (but not exactly equal) to these calculations.


My tests were not as "scientific"... we made a scale sort of thing and simply had guys shoulder and stress the rifle with the rear pin out :eek:

If you would like to discuss it off line, I would be happy to... but as stated, for all intents and purposes, this test and the thread are over -- I have asked the staff to lock it.