View Full Version : Phosphate under gas block
I see people give negative points when a company does not phosphate under the gas block. One good reason to not phosphate under the gas block is that phosphate adds a tolerance to the calculation, so if you can skip the phosphate under the block, you can design in a smaller variation in gas block to barrel fit. 'Just saying. Things are not always what they seem.
Robb Jensen
12-03-11, 05:07
Exactly. I've yet to see where the lack of finish in that area has caused any issue with the function of the rifle, corrosion or any issues which caused the barrel to be removed from service. People that complain about the lack of finish there are probably those who complain about brass on the brass defector.
That is funny. There are people who prefer their rifles to not be factory test fired.
I see people give negative points when a company does not phosphate under the gas block. One good reason to not phosphate under the gas block is that phosphate adds a tolerance to the calculation, so if you can skip the phosphate under the block, you can design in a smaller variation in gas block to barrel fit. 'Just saying. Things are not always what they seem.
What do you feel is an appropriate fit class for the barrel/gas block? RC4?
M Phosphate reference thickness is .0002"-.0004" buildup.
What do you feel is an appropriate fit class for the barrel/gas block? RC4?
M Phosphate reference thickness is .0002"-.0004" buildup.
More like RC1 - RC2.
Suwannee Tim
12-03-11, 19:20
When I found out my two Bushmasters had no finish under the gas block, I couldn't have cared less. I had occasion to remove one of the gas blocks and lo and behold, it was finished and I still couldn't have cared less. Then, just for grins I removed the other gas block and, yes, it was finished underneath too. Still couldn't have cared less. This was a learning experience for me as I had been misinformed by a certain internet resource that there was no finish under the gas blocks and I should care that there is no finish, both false. This same resource informed me that the gas keys would be unstaked or improperly staked, also false. This misinformation caused me to conclude that this resource was written less to inform the uninformed and more to justify the author's biases.
Careful... they'll hear you...
http://i1235.photobucket.com/albums/ff438/wood_911/zombies_colt.jpg
Just kidding :lol:. I would assume it's possibly an area where rust could occur?
Not really. Park mainly only stops rust when it is holding oil anyway.
My LMT isnt parked, and I dont care, ive never had problems. Not having it parked made it easier for me to replace the fsb with a low pro gb. Thanks for your insight and experience rsilvers, its guys like you that really makes m4c what it is
Careful... they'll hear you...
http://i1235.photobucket.com/albums/ff438/wood_911/zombies_colt.jpg
Just kidding :lol:. I would assume it's possibly an area where rust could occur?
Ok thats pretty damn funny right there.
More like RC1 - RC2.
...Plus extra allowance for the nominal thickness of any coating(s).
I think more than anything it's beneficial in that it shows attention to detail/TDP/etc. In a similar manner that MPI really has little benefit these days when failure rates are statistically zero, and properly dimensioned parts are far more important.
If the intent of building a gun is to adhere to the TDP as much as possible, if they neglect to parkerize the area under the gas block, what other steps/procedures/dimensions/tolerances do they neglect as well. I agree there is probably little benefit, but the fact that they do something so trivial probably also means they pay attention to other seemingly trivial details that may, in fact, affect the function of the gun.
Of course there are also exceptions such as LMT that still produce excellent products despite overlooking some parts.
I like M4s - both to use, and also for retro collection purposes. If you want one - I would suggest a 6921 - not an attempted clone of it from another company.
But let's face it - it came out in 1994 - the car of the year was the Toyota Supra. Would you all be trying to buy 1994 Supra's in 2011? No.
Colt knows the M4 is not the best way to make a rifle - that is why their IC competition rifle has improvements.
What if the designer preferred the ability to have a more precise fit between the barrel and gas block? How does that mean they are not paying attention to details?
What if the designer preferred the ability to have a more precise fit between the barrel and gas block? How does that mean they are not paying attention to details?
Notice I specifically mentioned the TDP, the standard by which guns are judged around here.
I probably should have mentioned KAC as a counter-point, as they heavily diverge from the standard yet are an excellent product/design.
Without the baseline, how do you know that their intention is for a more precise gas block to barrel fit? How do you know they are not just lazy? Without other qualifiers you can't make that distinction.
Also, I wouldn't use a car like a Supra as an analogy. There are people selling early 90's Supra's for $30k+ on up to one I saw for $82k, a 1994. Pick a less desirable car, people aren't interested in building 8 second '94 Honda Civics like they are Toyota Supra's and R32 Skyline's.
Without the baseline, how do you know that their intention is for a more precise gas block to barrel fit? How do you know they are not just lazy? Without other qualifiers you can't make that distinction.
True, but neither can everyone who complained about not having park under the gas block. How do they know it was not done to have a more precise fit?
Also, I wouldn't use a car like a Supra as an analogy. There are people selling early 90's Supra's for $30k+ on up to one I saw for $82k, a 1994. Pick a less desirable car, people aren't interested in building 8 second '94 Honda Civics like they are Toyota Supra's and R32 Skyline's.
I would only pick a less desirable car if I wanted to bash the M4, and I do not. I like the M4. The 1994 Supra was the best at the time, and so was the M4. The 1994 Supra is very desirable today with certain people, and so is the M4. The 1994 Supra, however, has things that would be done differently if it were made today, and so should the M4. I am not a fan of the stepped barrel, for example. And I prefer nitrided barrels over chrome lined. And I would tend to use a low profile gas block over a FSB. And the CTR stock is better than the M4 stock. And I would use more of a mid-length gas system. And more can be done with advanced finishes on the working parts. And Geissele triggers are better than the stock ones.
You guys sure know how to BS over minutia.
If gas-block fitment (to that kind of precision) made a damn bit of difference they'd be made to interference fit.
davidjinks
12-04-11, 09:15
Wouldn't it also be fair to say that just because YOU prefer XYZ doesn't mean someone else would? What makes the design changes that you have superior to what they are right now?
I understand where you're coming from. Please don't take this as an argument. Just pickin your brain...
I would only pick a less desirable car if I wanted to bash the M4, and I do not. I like the M4. The 1994 Supra was the best at the time, and so was the M4. The 1994 Supra is very desirable today with certain people, and so is the M4. The 1994 Supra, however, has things that would be done differently if it were made today, and so should the M4. I am not a fan of the stepped barrel, for example. And I prefer nitrided barrels over chrome lined. And I would tend to use a low profile gas block over a FSB. And the CTR stock is better than the M4 stock. And I would use more of a mid-length gas system. And more can be done with advanced finishes on the working parts. And Geissele triggers are better than the stock ones.
Wouldn't it also be fair to say that just because YOU prefer XYZ doesn't mean someone else would? What makes the design changes that you have superior to what they are right now?
Yes, the market should decide - what I am trying to counter though is people saying something should be avoided because it is not on a product that is, by contract, not allowed to change since 1994.
davidjinks
12-04-11, 13:51
I agree. Personally, the way I have read A LOT of information on M4C is the "Mil Spec" is the level that you should never go under. Better is always good...less is well...less.
Thanks for your information!
Here's another question for you:
How much better would your changes be over what the "Standard" is?
For this, I'll consider the "Standard", milspec. Just to pick one thing, let's say nitriding over chrome lining.
Yes, the market should decide - what I am trying to counter though is people saying something should be avoided because it is not on a product that is, by contract, not allowed to change since 1994.
Most here know I don't really care very much about meeting specs exactly... I care about the specs that matter, and ignore those that don't. This is one of those that, for the most part, doesn't matter.
I have worked on lots of ARs... The only time phosphating under the FSB has ever made the least bit of difference is when replacing the FSB with a gas block that has a different barrel footprint. Sometimes we'd have to Alumablack the barrel in the area that used to be covered, but no longer was.
For that reason, I prefer them to be phosphated under the FSB... but that's a cosmetic issue, not a functional one.
When I get home I'll check the barrel and FSB prints and see what the post Park finish ream diameter is on the FSB bore compared to the post Park diameter of the seat.
ETA: print doesn't state that the dim on the barrel is after Parkerizing, I doubt it is, but the seat (M16A1) is called at 0.6238" +/- 0.0005" and the hole in the FSB is 0.6249" + 0.0005" after Park and hone. . Which makes the maximum allowable mismatch 0.0021". How much thickness can phosphate be expected to add?
When I get home I'll check the barrel and FSB prints and see what the post Park finish ream diameter is on the FSB bore compared to the post Park diameter of the seat.
ETA: print doesn't state that the dim on the barrel is after Parkerizing, I doubt it is, but the seat (M16A1) is called at 0.6238" +/- 0.0005" and the hole in the FSB is 0.6249" + 0.0005" after Park and hone. Which makes the maximum allowable mismatch 0.0021". How much thickness can phosphate be expected to add?
M Phosphate reference thickness is .0002"-.0004" buildup.
And the minimum clearance is .0006".
This is pretty much a RC2B fit plus a .00035" coating allowance for the barrel.
The "B" fit knocks a grade off the hole diameter (~.0001) to allow for tool wear.
And then the shaft tolerance range expanded from only .00025 to .001", probably to lower manufacturing cost.
Phosphate is 0.0002 to 0.0004 per side. So on the barrel, it will add to the diameter by 0.0004 to 0.0008.
The "cost" of this is that it adds in a variable which can vary by 0.0004 on top of the barrel and gas block machining variance. So you have to allow for that in the barrel, and have to design in what amounts to a larger gap in the end a greater percentage of the time.
Now you may say "Well, it seems to work," but Colt allows for rifles to be from 700 to 950 rpm cyclic rate before they ship. No doubt, some of this wide cyclic rate variation is due to varying amounts of gas leakage.
One could argue that by not putting Park under the gas block, the production rifles would have less gas leakage on average, and hence less variation in cyclic rate. Whether this is actually a significant factor, I don't know - but if an engineer decided not to Park under the gas block for this reason, I would think that is a reasonable decision.
Clint,
Most of that went right over my head. ;)
Back in '98 when I first brought up BFI's lack of phosphate under the FSB it was to illustrate their lack of compliance with the mil spec when they were, at the time, climbing high on the milspec wagon. Funny to see how many have run with that in the intervening decade.
Parkerizing the FSB in place is faster and less prone to create cosmetic flaws than Parking the parts separately and then mounting the FSB. But, at best it shows a lack of adherence to the spec and at worst leaves bare, inaccessible steel that has been exposed to water, heat, and acid through the Park process. Little shortcuts like that add up to a less expensive product.
.
Just wondering...how is that small little area on the barrel under where the FSB will reside not park'd when the rest of the barrel is?
Is it park'd with the FSB in place, is it taped off, milled off, ...?
.
Parkerizing doesn't creep very much and doesn't like to stick to un prepped metal.
What is really accomplished with the tighter fit? Has testing shown any repeatable results that are desirable, or even noticeable?
This whole discussion is missing the point. Why does Colt, for example, have park under the FSB?
BECAUSE it was assembled correctly. The pin holes are reamed after the barrel nut is torqued and the barrel is in place. This makes the FSBs truer on a factory Colt gun than the aftermarket stuff.
The corrosion protection is largely negligible... and this gas leakage notion is absurd.
The corrosion protection is largely negligible... and this gas leakage notion is absurd.
Let's talk to the gas leak for a moment. How is the seal at the gas tube? What happens when we weld the gas block to the barrel? Any gains? What sort of ammo does one need to shoot to reap the benefits of the better seal at the gas block? Why is there a range on the acceptable cyclic rate? Is it because of the gas block seal or because of the variances in ammo, variances in locations where the gun will be shot, variances in the acceptable gas port size, variances in the carrier/gas ring interface? Tolerances stack fast and the cyclic rate is the very end result of a pile of stacked tolerances.
Gas will leak... eventually the carbon build up will equalize most guns though.
People will also discount the use of taper vs. straight pins. Taper pins, when used correctly will help pull the FSB down onto the gas port.
Discounting these little details means more than most people realize.
Another good detail, what is the real difference once the hypothetical improved block is installed and pinned vs current practice.
How many pieces can you split an atom into?
Considering the institutional inertia of gov't entities, its hard to make changes. Is there better than mil-spec? Sure, we have a several page discussion on it here. The fundamental idea that is reiterated over and over is that mil-spec is the lowest acceptable standard. Following the current TDP produces a proven weapon. Any time a change is introduced, there is the potential for problems to arise (Automotive industry?)
If company XYZ can't meet the lowest acceptable standard, what standard are they meeting? The technical benefit of park under the fsb is moot. The fact is that not doing is taking a shortcut which begs the question: What other shortcuts are being taken? How do you know that shortcuts aren't being taken on things that are of technical value such as the steel composition in the bolt and barrel or the shot peening and heat treatment methods used on certain parts? There are many finer points than whether or not the barrel is parked under the fsb. The devil is in the details.
Suwannee Tim
12-05-11, 18:44
Now that I have informed you that Bushmaster properly stakes their gas keys and coats the barrel under the gas block will you concede that Bushmasters are excellent firearms, fully the equal of Colt? No? I didn't think you would.
Not coating the barrel under the gas block is nothing more than a process choice which probably has little significance one way or the other. Folks are eager to believe that this simple indicator provides a simple answer to a complex question, that question being "how do you evaluate the quality of an AR?" Like all complex questions, there are many simple answers, and they are usually wrong.
I know I am a nobody. I know I don't know anything. That being said, I respectfully disagree.
While it is true that you will get a "slightly" tighter fit without it, we have all seen the photos of damage to guns that were not parked under the FSB when exposed to harsh conditions.
Does it have to be Parkerizing? No. But there needs to be some kind of finish under there, just like there should be on the rest of the gun.
Now give me a moment please while I go find my nomex to put on.
mil-spec is the lowest acceptable standard.
Exactly, so leaving out items called for in the spec is less than acceptable. <G>
Since all parties agree that Parkerizing adds thickness how does that create a looser seal? :confused:
Exactly, so leaving out items called for in the spec is less than acceptable.
If you are building an M4 - sure. If you are building a great AR - there are several ways to do it. For example, leaving out the M203 step - bad for an M4, good for most other ARs.
Since all parties agree that Parkerizing adds thickness how does that create a looser seal? :confused:
Because you have to allow for the variation in thickness. Since the diameter change can be from 0.0004 to 0.0008, you have to "allow for" 0.0008. So if it is less than that (and it will be most of the time), then there is an increased gap.
Because you have to allow for the variation in thickness. Since the diameter change can be from 0.0004 to 0.0008, you have to "allow for" 0.0008. So if it is less than that (and it will be most of the time), then there is an increased gap.
Does this gap do anything?
I don't know, but I suggested that reducing it may make it easier for the cyclic rate variation to be narrowed from 700-950 to some tighter spec.
My point in starting this thread was that rifle designers should have the option to want to reduce this gap by eliminating the Park under the block - and that was a reasonable decision to make.
I don't know, but I suggested that reducing it may make it easier for the cyclic rate variation to be narrowed from 700-950 to some tighter spec.
I guess the better question is why is the spec 700-950. The next one would be what else can impact that number. I think if you make a list the gas block fit is pretty close to the bottom.
My point in starting this thread was that rifle designers should have the option to want to reduce this gap by eliminating the Park under the block - and that was a reasonable decision to make.
They do, don't they? What is to stop AAC from doing so? If you build it they will buy it. The question should be is it for a measurable and repeatable result or for cost savings? Then the other question is how much does this "better" fit cost the consumer? I have been pretty fortunate to be around quite a few guys who know these guns and none of them had complaints about poor gas block fit...
And more so, to how many people does the cyclic rate matter?
I, for one, don't expect anything but a USGI rifle, or one purporting to be built to the same standard, to be Park'd under the FSB. Apples and oranges. As I said, when I brought this up a long ago, much to the BFI rep' consternation, it was as a warning to buyers that all "milspec" ain't necessarily so. It's more of the "just as good but cheaper" sales pitch that is so prevalent these days.
Would I be expected to believe that Colt's CR6724 is a POS because it lacks a finish under the gas block?
Do I care? Not in the least, if anything a cheaper version of the rifle will get more people into using them.
As to cyclic rates, I built a lot of FAs at OAI and their rates varied wildly, anywhere from a chug to a zip, and none of those were Park'd under the barrel. Apparently, there are a lot bigger issues there than where the finish is.
As to cyclic rates, I built a lot of FAs at OAI and their rates varied wildly, anywhere from a chug to a zip, and none of those were Park'd under the barrel. Apparently, there are a lot bigger issues there than where the finish is.
That is kind of the point I am making. This is normally where someone would call for some testing before investing much more thought into the idea.
Look at the post times, you were making your point while I was composing mine. ;)
And more so, to how many people does the cyclic rate matter?
Oh my gosh. That is one of the main factors effecting reliability.
As to cyclic rates, I built a lot of FAs at OAI and their rates varied wildly, anywhere from a chug to a zip, and none of those were Park'd under the barrel. Apparently, there are a lot bigger issues there than where the finish is.
My comments were only relevant to reducing standard deviation of cyclic rate within one product line.
Oh my gosh. That is one of the main factors effecting reliability.
No ****ing shit. What does it matter if the acceptable range is between 700-950? To whom will it make a real difference if that rate can become between 800-820? What proof do we have now that the gas block is the biggest factor in that variance? What kind of ammo would one need to shoot to have their cyclic rate fall within the number you decided was a goal? What kind of spring life will there be on the buffer spring in order to maintain said acceptable range? What is the barrel life as the gas ports erode? What is the gas ring life?
Exactly. I've yet to see where the lack of finish in that area has caused any issue with the function of the rifle, corrosion or any issues which caused the barrel to be removed from service. People that complain about the lack of finish there are probably those who complain about brass on the brass defector.
yeah that brass on the deflector is really bad. especially if the ejection pattern is at 3:00 instead of the more accepted 4:00...
:cool:
within one product line.
These were.
No ****ing shit. What does it matter if the acceptable range is between 700-950? To whom will it make a real difference if that rate can become between 800-820?
The reason why it is 700-950 is because 825 is the optimum, but they allow a variation of +- 125 rpm. It would be better if this variation were lower, but due to things like variations in the spring rate, the BCG part's mass, gas leakage, and ammo variation - they have to give a wide range or else too many guns would be rejected.
If the range can become 800-850, then average reliability will go up. I did not say that gas block leakage was a significant factor in this. I said that it may be, and the rifle designer has the tool of a more precise fit as an option to look at.
I imagine if someone worked at a company that had access to guns and some equipment said person could easily have a few different guns set up and answer the question pretty quickly. I would also be curious as to how much the average reliability would go up. You can play statistics and speculate all day long, at some point you need to pull triggers and do something.
I agree that it could contribute but there seems to be a much longer list of things that would contribute more. If AAC wants to come out with a gun that doesn't have a coating under the gas block who cares, people will buy it.
Colt already knows exactly how much reliability goes up with a more optimal cyclic rate. Likewise, when we developed our 300 BLK guns we did a week of high speed video studying this.
AAC barrels are nitrided, so that adds no thickness, and so we already don't have to deal with a coating layer.
We also control the bore cross sectional area to a drawing, and likewise, a layer of chrome would raise the variation in bore dimensions.
What else has been tweaked in trying to reach the cyclic rate chosen?
What are the ammo limitations within that ideal cyclic rate?
It is not a question of reaching the cyclic rate. That was done 20 years ago when they picked the buffer weight and gas port size.
I am speaking of reducing cyclic rate variation. Aside from ammo, which is made by someone else, the gun maker just has to try to make the rifles as identical as possible.
The reason Colt got an unfair deal in the 'dust' tests was that the govt picked M4s off the shelf that had cyclic rates at or below 700 rpm, and competed them against XM8s and SCARs which were specially prepared by Hk and FN for this event - no doubt with cyclic rates optimal for dust tests (higher rates).
I have to wonder, how would M4s have done if they started at 900 rpm rather than 700 rpm? Almost certainly better.
Because you have to allow for the variation in thickness. Since the diameter change can be from 0.0004 to 0.0008, you have to "allow for" 0.0008. So if it is less than that (and it will be most of the time), then there is an increased gap.
This is all true.
But in the M16A1 case, the bore dimension is " hone to size after phosphate coating".
This eliminates variation from one side.
The .00035 allowance on the barrel is slightly less than the max, but this is OK because phos is friable(crushable).
So the extra variation in the setup amounts to .00015", or the diff between the allowance an the min thickness.
Thats not much considering the bore is allowed .0005" and the shaft .001".
That eliminates hole variation, but when I said the variation was on both sides, I did not mean the shaft and the hole, I meant both sides of the shaft. Since Phosphate is 0.0002 to 0.0004 per surface, that is 0.0004 to 0.0008 increase in diameter of the shaft.
AAC barrels are nitrided, so that adds no thickness, and so we already don't have to deal with a coating layer.
Just out of curiosty, what sort of 'nitriding' are you guys using? Is this like a nickel boron nidride, or a ferritic nitrocarburizing, or something else alltogether?
Ferritic nitrocarburizing, but with a very specific process to not harm the barrels. The way it is often done terrifies me. There are very few companies I would buy a nitrided barrel from.
What is the profile of the barrels AAC will be using?
That eliminates hole variation, but when I said the variation was on both sides, I did not mean the shaft and the hole, I meant both sides of the shaft. Since Phosphate is 0.0002 to 0.0004 per surface, that is 0.0004 to 0.0008 increase in diameter of the shaft.
Right you are.
Ferritic nitrocarburizing, but with a very specific process to not harm the barrels. The way it is often done terrifies me. There are very few companies I would buy a nitrided barrel from.
What's so terrifying about a thousand degree molten lava salt bath dunking?:blink:
What is the profile of the barrels AAC will be using?
It is our own profile - a light one.
Think of it as an extra stress relief soak. But yes, a lot of things have to be controlled.
Slight OT, but does AAC have any intentions of releasing complete rifles besides the honey badger? I can appreciate the obvious research you guys are putting in...and getting out of the comfort zone. I would be prone to giving any AAC complete rifle a try because your grasp on the details and willingness to discuss them inspires confidence. Just curious.
Yes, we will have rifles like this as a factory SBR. There will be a 12.5 and 16 inch also.
http://img521.imageshack.us/img521/9564/img7117urlsmall.jpg
I would be very surprised if Colt did not use S2.
This stuff is fresh on my mind, as I have been carefully picking each part - right down to the pins and springs. My goal is to share information on little known but interesting things.
Now that I have informed you that Bushmaster properly stakes their gas keys and coats the barrel under the gas block will you concede that Bushmasters are excellent firearms, fully the equal of Colt? No? I didn't think you would.
Not that I believe you, but you think because Bushmaster accidentally staked one bolt carrier correctly that they are now built to a standard? Put down whatever it is you're smoking and get real. What's sad (pathetic) is that they could build a rifle to a standard, but they choose not to.
Suwannee Tim
12-07-11, 15:50
Not that I believe you, but you think because Bushmaster accidentally staked one bolt carrier correctly that they are now built to a standard? Put down whatever it is you're smoking and get real. What's sad (pathetic) is that they could build a rifle to a standard, but they choose not to.
I made the assertion to illustrate a point, not get into a discussion of Bushmaster but if you insist, I'll play for a little while...... Bushmaster properly stakes their carrier keys and has done so for some time. I have one, just sold another and have examined dozens of them at the range and in guns shops and have yet to see one with an improperly staked or unstaked carrier key. I am told that Bushmaster has sold rifles with unstaked keys which I have no reason to doubt. For some folks, presumably including you BKennedy, that act was a sin so unforgivable that it will stain Bushmaster's reputation for ever and ever. On another thread there is a discussion of Colt guns with barrel nuts improperly tightened. Is that a sin so unforgivable that it will stain Colt's reputation for ever and ever? No? I didn't think so. I have questioned a couple of dozen Bushmaster owners over the last couple of years, several of them Service Rifle shooters who shoot a lot and are very demanding of their guns. Every Bushmaster owner I have questioned has been satisfied with their gun. If you want to nurse a seething hatred of Bushmaster then do so but don't deceive yourself that your opinion is fact based. You are entitled to your own opinion but you are not entitled to your own facts.
No hate Tim, and I never said they don't stake their carrier keys, I implied that they don't stake them correctly. I also used to shoot Highpower and I would hardly call that demanding. I won't bore you with the speech on why things are built to a standard, and why those that aren't usually fall short because you are obviously very emotionally tied to your Bushwhacker. If works for you, drive on, but don't pretend it's built to the same standards that the Colt is.
Sorry for the derail.
Suwannee Tim
12-07-11, 19:14
.....you are obviously very emotionally tied to your Bushwhacker......
The only thing I am emotionally tied to in this thread is the truth. I have half a Bushie left, a .450 upper, my Bushie rifle is gone, sold. I've got more Colts than Bushies now. Two Colts versus half a Bushie.
I just can't fathom how there can be so much joy in degrading Bushmasters day after day... No, I don't own one. No, I never owned one. No, I never sold one. Yes, I know one person who has one.
I enjoyed playing the "it's not to spec!" game for a couple years... but it gets boring after a while and you start to care more about what works and less about what the data sheet says.
If for some reason all I could get was a Bushmaster.... I'd swap the bolt assembly to a Mil-Spec one, drop a 5.56NATO chamber reamer in it, stake the gas key and castle nut, and possibly add a heavier buffer. I'd make sure I had good magazines, ammunition, and generously lubricated it. ...It isn't my first pick, but can anyone explain exactly what about that is so failure-prone that it isn't a perfectly functional rifle for 99% of people, including many non-extreme defense roles?
I mean, really, worrying about the finish under the gas block? Who cares?
If for some reason all I could get was a Bushmaster.... I'd swap the bolt assembly to a Mil-Spec one, drop a 5.56NATO chamber reamer in it, stake the gas key
I am not really up on what Bushmaster does. Do we know they are 223 chambers? It would seem more likely they are 5.56mm.
Would you really ream a chrome lined barrel?
Would you really toss a Bushmaster bolt without checkin it? How do you know it is not mil spec now?
Why would you stake the carrier key when it is already staked?
I am not really up on what Bushmaster does. Do we know they are 223 chambers? It would seem more likely they are 5.56mm.
Would you really ream a chrome lined barrel?
Would you really toss a Bushmaster bolt without checkin it? How do you know it is not mil spec now?
Why would you stake the carrier key when it is already staked?
If it is 5.56NATO already, it will be unaltered. If it is not already 5.56NATO, then I have no qualms with reaming a chromed chamber. It is hard chrome so there is no flaking risk, and the throat is the main difference which is quickly eroded anyway. Trust but verify-
Bushmaster, last I looked, doesn't even claim 158 Carpenter steel. They definitely never mentioned any HPT or MPI that I saw. (Not that I place great emphasis on those tests... but generally the companies that perform them are offering a quality bolt.)
Depending on the quality of the staking, I may stake it better. Or, I may add redundant staking on the top in the "field expedient" or "counter-staking" fashion.
Obviously, if something is already done and done correctly I'm not going to change it....
Bushmaster absolutely uses C158 steel - whether they advertise it or not is another matter.
As for HPT - yes, they certainly do that.
As for MPI - I don't actually know. The Brownell's catalog says they do, but it would not be the first time a description was incorrect.
Depending on the quality of the staking, I may stake it better. Or, I may add redundant staking on the top in the "field expedient" or "counter-staking" fashion.
Just try to unscrew the screws with 55 inch-lbs of torque. If the screws don't move, the staking is good.
Bushmaster absolutely uses C158 steel - whether they advertise it or not is another matter.
As for HPT - yes, they certainly do that.
As for MPI - I don't actually know. The Brownell's catalog says they do, but it would not be the first time a description was incorrect.
Even if it does pass those, if it is heat-treated too deep it will be brittle... the cracks may not appear initially to be seen on a MPI. Give it a couple hundred rounds and *snap*, there went your bolt.
A new bolt is $65, and it is arguably the most sensitive part of the rifle as far as how well it needs to be made and how easy it can be to screw it up- and it is absolutely 100% critical to function. Personally, I'll pay my $65 to get a BCM bolt (along with the good extractor spring and insert) and not worry about it. Keep the original as a spare.
It is very unlikely that a BCM bolt is better than a Bushmaster bolt.
Just try to unscrew the screws with 55 inch-lbs of torque. If the screws don't move, the staking is good.
... I hate to argue with someone with credentials such as yourself on technical matters... but staking is there in the event that over time the screws wiggle loose. Staking is not to tighten the screws.
(along with the good extractor spring and insert)
Which spring is good?
It is very unlikely that a BCM bolt is better than a Bushmaster bolt.
Okay... I still don't trust Bushmaster for such a critical part. If you wouldn't change it... don't. Personally, I would.
Which spring is good?
Gold/Five Coil.
Black insert, and possibly a Crane O-ring.
... I hate to argue with someone with credentials such as yourself on technical matters... but staking is there in the event that over time the screws wiggle loose. Staking is not to tighten the screws.
The military standard is that the stakes should not distort the side surfaces, and they should result in a removal torque no less than 55 and no more than 100 inch-lbs. So the goal of staking is not to keep the screw from moving, but rather to keep it from removing with less than 55 inch lbs of torque. And if it takes more than 100 inch lbs, then the staking was too much.
Okay... I still don't trust Bushmaster for such a critical part. If you wouldn't change it... don't. Personally, I would.
They are making good bolts.
The military standard is that the stakes should not distort the side surfaces, and they should result in a removal torque no less than 55 and no more than 100 inch-lbs. So the goal of staking is not to keep the screw from moving, but rather to keep it from removing with less than 55 inch lbs of torque. And if it takes more than 100 inch lbs, then the staking was too much.
Mmm... I haven't brushed up on the specs in a while, and don't care to look them up tonight.
My understanding is that the screws should be torqued to about 55 inch lbs... So, assuming they went over a bit, 55 inch lbs exactly wouldn't remove them... staking or no staking.
The staking is there to save your butt if the get loose from some reason over time, or were not torqued properly to begin with. Properly torqued gas key fasteners, in a perfect world, would not need staking at all. Staking is a backup.
They are making good bolts.
Alrighty then... If I ever have a Bushmaster, I'll trade you my bolt for a BCM. Then we can both be happy. ;)
Properly torqued gas key fasteners, in a perfect world, would not need staking at all. Staking is a backup.
Agreed, but once staked, the screws should be removable with between 55 and 100 inch lbs of torque.
Agreed, but once staked, the screws should be removable with between 55 and 100 inch lbs of torque.
We are in agreement, then.
Gold/Five Coil.
Black insert, and possibly a Crane O-ring.
I never felt comfortable referring to spring by the number of coils when the drawing says that the number of coils is a REF and it changes from batch to batch.
I ran spring analysis software on pretty much all extractor springs in the Brownell's catalog. The newer military gold one was not bad but still over-stressed (over 45% of MTS). There are some absolutely horrifyingly bad extractor spring designs in some of 'your' favorite bolts (I don't mean you specifically, lamarbrog). Some were at 80% of MTS.
I was not able to buy the spring that I wanted in the AAC bolt - had to have it made. Basically, the AAC spring is the original M16 spring design (which is not overstressed). Except I had them made from MountJoy brand Rocket Wire to make it even lower % of MTS, and then the extraction force was raised to carbine standards without adding additional stress to the spring by the o-ring.
I pull all other springs out of bolts, including the newer gold military ones.
Alrighty then... If I ever have a Bushmaster, I'll trade you my bolt for a BCM. Then we can both be happy. ;)
I wish there was a way for you to CMM them both, but those machines are $75K.
I never felt comfortable referring to spring by the number of coils when the drawing says that the number of coils is a REF and it changes from batch to batch.
I ran spring analysis software on pretty much all extractor springs in the Brownell's catalog. The newer military gold one was not bad but still over-stressed (over 45% of MTS). There are some absolutely horrifyingly bad extractor spring designs in some of 'your' favorite bolts (I don't mean you specifically, lamarbrog). Some were at 80% of MTS.
I was not able to buy the spring that I wanted in the AAC bolt - had to have it made. Basically, the AAC spring is the original M16 spring design (which is not overstressed). Except I had them made from MountJoy brand Rocket Wire to make it even lower % of MTS, and then the extraction force was raised to carbine standards without adding additional stress to the spring by the o-ring.
I pull all other springs out of bolts, including the newer gold military ones.
Could you explain this in a little simpler terms? Extractor springs are one of those things I am very interested in, but know fairly little about.
I wish there was a way for you to CMM them both, but those machines are $75K.
I assume you are referring to a Coordinate Measuring Machine?
I don't doubt that they are dimensionally the same. Heck, they might be sourced from the same manufacturer.
What counts more so is the processing after the initial machining. Shot peening, heat treatment, and to a lesser extent HPT and MPI.
There is this $700 spring design software that I use:
http://www.smihq.org/public/software/asd6.html
All of the extra power extractor springs that are popular - I bought them and put them into the software - and it flags them as outside of good engineering practice.
The original M16 spring, however, was clearly designed by someone who knew what they were doing, as the software says it is great and has stress within normal limits.
The problem is, carbines need more extractor force than the M16, so the original M16 spring is not quite good enough. There are two ways to solve it - use a stiffer spring (but then they are over-stressed because, given the tiny cavity they sit in, wire of a desirable thickness will no longer fit for these springs with more force) - or use an o-ring with the original spring.
The o-ring is the correct solution, and not a gimmick - as it is the only solution where you get more extractor force without a spring design that is over 45 percent of the material's tensile strength.
We went one step further, and made the original spring out of higher grade wire - Rocket Wire, but did it without making it stiffer, so the higher grade material serves simply to make it last even longer.
Shot peening is super important, but I don't think any of your favorite companies shot peen their own bolts.
There is this $700 spring design software that I use:
http://www.smihq.org/public/software/asd6.html
All of the extra power extractor springs that are popular - I bought them and put them into the software - and it flags them as outside of good engineering practice.
The original M16 spring, however, was clearly designed by someone who knew what they were doing, as the software says it is great and has stress within normal limits.
The problem is, carbines need more extractor force than the M16, so the original M16 spring is not quite good enough. There are two ways to solve it - use a stiffer spring (but then they are over-stressed because, given the tiny cavity they sit in, wire of a desirable thickness will no longer fit for these springs with more force) - or use an o-ring with the original spring.
The o-ring is the correct solution, and not a gimmick - as it is the only solution where you get more extractor force without a spring design that is over 45 percent of the material's tensile strength.
We went one step further, and made the original spring out of higher grade wire - Rocket Wire, but did it without making it stiffer, so the higher grade material serves simply to make it last even longer.
Very interesting. What are the repercussions of using a spring that is over-stressed? It just wears out faster? Breaks?
The O-ring is a modification that I absolutely believe in for carbines. My personal rifle is currently a 20" with rifle gas system (by choice, I specifically sought that configuration) so it is not of major concern to me... I use the 3-coil spring and a black insert. (And I don't think this is a genuine black insert... feels too soft.)
This is really neat information, I'm glad you're so open about sharing it.
I am a licensed aviation technician and deal with the issues of torquing and locking fasteners every day
Just try to unscrew the screws with 55 inch-lbs of torque. If the screws don't move, the staking is good.
ETA: My apologies to all on this forum. I posted the following which is incorrect-
The proper way to verify torque is to set the torque wrench to the correct torque and tighten.
Total torque of the gas key bolts is 55 in/lbs + torque from staking. Specification for torque + staking is 55 in/lbs - 100 in/lbs. Verification would require setting the torque wrench to the nominal torque, which is halfway between minimum and maximum. That would be 77.5 in/lbs. Rounding up to 80 is acceptable. Apply 80 in/lbs of torque after staking to verify final torque.
After posting, I realized that re-torquing a staked bolt is poor procedure. One, there is a risk of compromising the mechanical lock feature of the stake. Two, if the staking is on the minimum side, it would be possible to over-torque the bolt. The proper way to check the torque of a staked bolt would be to break torque, then torque using the proper procedures. It's been a long week with too little sleep
The following about torque wrenches is correct- It takes a special torque wrench to be certified accurate in a counter-clockwise direction. Most torque wrenches are designed to give an accurate reading in the clockwise direction only. Even if you were to verify torque by attempting to loosen, you should still tighten afterwards or better still, break torque completely and re-torque and re-stake.
... I hate to argue with someone with credentials such as yourself on technical matters... but staking is there in the event that over time the screws wiggle loose. Staking is not to tighten the screws.
...The staking is there to save your butt if the get loose from some reason over time, or were not torqued properly to begin with.
Staking is a mechanical lock to prevent the bolts from coming loose, not to catch them after coming loose. Properly staked bolts will stay torqued by increasing the amount of torque needed to remove (or tighten) the bolt
Properly torqued gas key fasteners, in a perfect world, would not need staking at all. Staking is a backup.
If this were true, Young carriers would be a good choice as they take steps to ensure the surfaces of the carrier mate to the surfaces of the gas key and use a sealant between them and torque to 55 in/lbs.
The staking is part of the torquing process. It gives a higher torque without stretching the bolt and threads to the point of failure and has the additional advantage of being a mechanical lock
Failure2Stop
12-08-11, 07:22
The reason Colt got an unfair deal in the 'dust' tests was that the govt picked M4s off the shelf that had cyclic rates at or below 700 rpm, and competed them against XM8s and SCARs which were specially prepared by Hk and FN for this event - no doubt with cyclic rates optimal for dust tests (higher rates).
Source for this?
Would you really ream a chrome lined barrel?
Absolutely.
You wouldn't?
Would you really toss a Bushmaster bolt without checkin it? How do you know it is not mil spec now?
Because there is absolutely no indication that it is to spec since they aren't individually tested.
Why would you stake the carrier key when it is already staked?
When the staking is insufficient to do the job.
Just try to unscrew the screws with 55 inch-lbs of torque. If the screws don't move, the staking is good.
What torque tools are you using to perform this task?
It is very unlikely that a BCM bolt is better than a Bushmaster bolt.
Support data?
Which spring is good?
Is this a question to legitimately seek information or to expose a lack of knowledge/information?
The o-ring is the correct solution, and not a gimmick - as it is the only solution where you get more extractor force without a spring design that is over 45 percent of the material's tensile strength.
Yet the o-ring has been repeatedly found to result in excessive extractor tension in real use.
Yet the o-ring has been repeatedly found to result in excessive extractor tension in real use.
With an original M16 rifle extractor spring?
With an original M16 rifle extractor spring?
I can't figure out why anyone would put an o ring on a rifle extractor spring in stead of just replacing the rifle spring with the 5 coil spring and Black/Green insert. :confused:
Because there is absolutely no indication that it is to spec since they aren't individually tested.
What do you mean by individually tested? Which maker verifies that each bolt meets all specs?
I can't figure out why anyone would put an o ring on a rifle extractor spring in stead of just replacing the rifle spring with the 5 coil spring and Black/Green insert. :confused:
The rifle spring is the only one which has stress of less than a 45% of MTS.
Springs must not be referred to by the number of coils because they are reference values and change from batch to batch, even for the same design.
Source for this?
http://www.usni.org/magazines/proceedings/2010-07/what-really-happened-wanat
According to officials at Colt, those reasons included the fact that six of the ten M4s drawn for the test did not meet the minimum rate of fire of 700 rounds-per-minute mandated under Mil-Spec IAW Mil-C-70599A(AR), which requires a cyclic rate of fire of 700 to 970 rounds-per-minute. The M4s used in Dust Test 3, delivered to the Army in June 2007, met mil-specs when delivered; however, together the ten drawn for the test from the U.S. Army inventory averaged only 694 rounds-per-minute.30 While performing comparably with the HK416, XM8, and Mk16 in all other respects, the M4 carbines used in the test experienced a large number of failure-to-feed and failure-to-extract stoppages.31 Colt says this is because of the sub-mil-spec rate-of-fire of the test weapons.
Colt also states that ATEC's testers were unfamiliar with the M4s' 3-round burst configuration which, depending on the position of the cam, will sometimes fire 1 round or a 2-round burst before firing a 3-round burst. This unfamiliarity, said Colt, led to single rounds and 2-round bursts being counted as stoppages. With the exception of the M4s, all other weapons tested were fully automatic with no 3-round burst provision. Further, Colt points out that the test itself did not meet Mil-Spec 810F and "was not repeatable."
In response to what Colt described as "the premature media reporting" of the raw test data, Program Executive Office Soldier suggested that Colt conduct its own extreme dust test. So Colt contracted a DOD-certified testing agency, Stork East-West Technology Corporation in Jupiter, Florida, to conduct its own dust test according to mil-spec guidelines. In this test of ten M4 carbines, which was conducted under a protocol identical to that used in Extreme Dust Test 3, only 111 stoppages were reported.
When the staking is insufficient to do the job.
Of course, but it is unlikely to be insufficient.
I guess we can go back for years and find bad examples - but no one has yet shown they can go buy a new Bushmaster and that the staking would fail the test that MistWolf described - applying 80 inch-lbs of tightening torque and seeing the bolt move.
Failure2Stop
12-08-11, 08:27
What do you mean by individually tested? Which maker verifies that each bolt meets all specs?
I hate to answer a question with a question, but are you saying that Colt does not?
http://www.usni.org/magazines/proceedings/2010-07/what-really-happened-wanat
I was more referring to the assertion that HK and FN intentionally modified their submissions.
Of course, but it is unlikely to be insufficient.
I guess we can go back for years and find bad examples - but no one has yet shown they can go buy a new Bushmaster and that the staking would fail the test that MistWolf described - applying 80 inch-lbs of tightening torque and seeing the bolt move.
This test could easily be passed without ever staking the key, so I am not all that convinced that the test proposed proves anything useful. Frankly, I would rather just have the gas key be an integral part of the BCG, as I have no need to ever swap them and it would remove a potential failure point. However, that is neither here or there. What I have seen is those with visually weak staking (such as BM) have gas keys shoot loose. Haven't seen it ever in extremely high round count Colt M4s or M4A1s, which to me seems to imply that someone is doing it right and someone else isn't.
With an original M16 rifle extractor spring?
Just spring or spring and buffer?
I hate to answer a question with a question, but are you saying that Colt does not?
I do not know how Colt makes their bolts so I am making assumptions - but it would be too expensive for them to test each bolt for each dimension on the manufacturing drawing. They would have to CMM each bolt - and that takes a while - so the normal thing to do is a statistical sampling on a CMM. Then there would be gauge points and an inspection drawing for the most common areas, so some or all of those areas would be checked for each one.
Failure2Stop
12-08-11, 08:45
I do not know how Colt makes their bolts so I am making assumptions - but it would be too expensive for them to test each bolt for each dimension on the manufacturing drawing. They would have to CMM each bolt - and that takes a while - so the normal thing to do is a statistical sampling on a CMM. Then there would be gauge points and an inspection drawing for the most common areas, so some or all of those areas would be checked for each one.
I was more talking about HPT/MPI, as it does a pretty good job of illustrating issues quickly.
This test could easily be passed without ever staking the key, so I am not all that convinced that the test proposed proves anything useful.
Maybe it does not prove anything useful in the field, but the torque test would prove that it meets the military requirements for coming-undone-ness - and was properly staked.
I was more talking about HPT/MPI, as it does a pretty good job of illustrating issues quickly.
That test is next to useless because essentially all bolts pass it, and a tougher test would be too destructive. Many of us have bolts in our ARs right now with thousands of rounds on them that would fail MPI if tested today, yet we still keep them in our rifles. AR bolts crack with use - they just do. We know today, but maybe not 50 years ago, what that means in real-world terms - that the bolt should be replaced at 5000 rounds for super hard use, or 10,000 rounds for typical use, or when it fails if we don't really care.
Just spring or spring and buffer?
I am asking if you think that an original M16 rifle spring, with an o-ring, and an insert - would have too much extraction force on an M4. Or if you just meant that that combination with a spring that was not an original M16 rifle spring would have too much force.
I was more referring to the assertion that HK and FN intentionally modified their submissions.
I would not use the term modify. HK had to build their XM8s for the test. They don't just have XM8s sitting around in inventory. Colt was the only party that did not have an opportunity to provide rifles.
I'm not sure why you're placing so much emphasis on CMM.
With the precision of modern manufacturing, the likelihood of a bolt being made that fails to meet dimensional specs is very unlikely. Factory test firing should reveal any major discrepancies anyway.
Obviously, HPT and MPI are a bit dated, and the notion that they might as well not be performed at all does have some merit. The idea being that any bolt that fails MPI when it is new is not going to last longer than a thorough test firing anyway.
The concern I have heard more often is that the heat treatment of a bolt can be too deep, causing it to be brittle. It won't be cracked, so won't fail MPI right away, but could break unexpectedly a few hundred rounds later. That is what concerns me- and is why I don't place nearly as much emphasis on HPT/MPI as I do trust in the company. For example, LaRue doesn't HPT or MPI, but I would probably use one of their bolts.
CMM as opposed to measuring another way? It is just easier/faster.
I think a part failing a dimensional check is about 10000 times (literally) more likely than a part failing MPI - yet some demand the MPI and don't demand the other. All of the MPI QC budget should go toward doing more useful checks.
I highly doubt LaRue does their own heat treat. They almost certainly send it to a heat-treat facility - just like everyone else.
CMM as opposed to measuring another way? It is just easier/faster.
Lamarbrog - I highly doubt LaRue does their own heat treat. They almost certainly send it to a heat-treat facility - just like everyone else.
Not so much the method- the process entirely. If the bolt fits, and passes test firing- the dimensions are probably good. Something being dimensionally wrong with a bolt is so far down on the list of things I worry about...
And I doubt LaRue does their own heat treating, too. But they likely contract it out to a reputable heat-treat facility, because they have a reputation for quality to uphold. Bushmaster and DPMS don't really have that same reputation.
militarymoron
12-08-11, 12:00
CMM as opposed to measuring another way? It is just easier/faster.
specifically designed go/no-go gauges would also work, depending on the tolerance. it's quicker than a CMM and doesn't require a person trained on the machine.
Not so much the method- the process entirely. If the bolt fits, and passes test firing- the dimensions are probably good. Something being dimensionally wrong with a bolt is so far down on the list of things I worry about...
I don't feel comfortable that is enough. It may work in that gun, and still be out of spec - and may effect the longer term reliability statistics and/or may not work in another gun. That is the benefit of interchangeable parts. For example, a bolt which is out of headspace may still be within headspace as a complete rifle for a particular barrel, but I would still want to reject that bolt.
And I doubt LaRue does their own heat treating, too. But they likely contract it out to a reputable heat-treat facility, because they have a reputation for quality to uphold. Bushmaster and DPMS don't really have that same reputation.
Let me tell you a story about McDonalds and why their $3.99 Lobster roll was always so good. The lobster suppliers would always give them first pick because they were afraid of losing such a big contract. One thing I am certain about is that suppliers to Bushmaster do want to give them the best quality work.
specifically designed go/no-go gauges would also work, depending on the tolerance. it's quicker than a CMM and doesn't require a person trained on the machine.
Also very low cost, low maintenance, etc. I would be shocked if companies in discussion weren't using them.
This excellent discussion on extractor springs has been moved/continued here
https://www.m4carbine.net/showthread.php?t=435&page=9
Failure2Stop
12-08-11, 14:51
I am asking if you think that an original M16 rifle spring, with an o-ring, and an insert - would have too much extraction force on an M4. Or if you just meant that that combination with a spring that was not an original M16 rifle spring would have too much force.
I don't have any data to support it, but I think you might be right that an original spring/buffer and o-ring would probably be just about right for a carbine length gas system.
Failure2Stop
12-08-11, 14:54
Maybe it does not prove anything useful in the field, but the torque test would prove that it meets the military requirements for coming-undone-ness - and was properly staked.
I'm trying not to get into a semantics argument on this one, so I'm just gonna leave it alone.
I don't have any data to support it, but I think you might be right that an original spring/buffer and o-ring would probably be just about right for a carbine length gas system.
I will need to dig a bit but I am all but certain that is true. If you follow the changes made to get the shorter barrels (gas port size, location, buffer weight, spring rate/length) it should all add up.
Failure2Stop
12-08-11, 15:02
That test is next to useless because essentially all bolts pass it, and a tougher test would be too destructive. Many of us have bolts in our ARs right now with thousands of rounds on them that would fail MPI if tested today, yet we still keep them in our rifles. AR bolts crack with use - they just do. We know today, but maybe not 50 years ago, what that means in real-world terms - that the bolt should be replaced at 5000 rounds for super hard use, or 10,000 rounds for typical use, or when it fails if we don't really care.
I have replaced somewhere around 15 broken bolts and dozens of others, all from guns used at my schoolhouse under my direct supervision. The ones that broke did not have round-counts on them, as my predecessors did not keep gun logs, so I can't comment on how many rounds on average it took to break a bolt, but on the ones we replaced, they were between 10 and 15k, or if they failed headspace but not throat erosion. I had barrels fail throat erosion before 10k.
I have never double pressure-tested a bolt. Have you?
I am asking out of curiosity since you brought it up. I don't think I have ever heard of anyone retesting after several thousand rounds.
Dimensional inconsistencies will create more stress in an AR bolt which lead to early failure. It's critical that not only the tolerances be held but that they are in control.
Being in tolerance is important. Dimensions must be within the minimum and the maximum. Just as important is control. If some bolts are at the minimum, some at the maximum and some somewhere in between, the manufacturing process is out of control. Will a simple go-no-go gauge identify an out of control process? Probably not, especially if the inspector is trained simply to look for a go or no-go condition.
Mr. Silvers, BM has a long way to go before they establish themselves as a top quality manufacturer. As you are a representative of ACC which, as I understand, is part of the Freedom Group, I'm certain you are going to defend BM as a sister company. That's understandable. However, you're playing to a tough crowd. Simply claiming that it's believed a certain manufacture does or does not perform certain tests is not enough, especially if it is not first hand knowledge. Whether Colt does or does not isn't important. What's important is that Colt has a proven track record, therefore what Colt does or does not does work. Bushmaster (and certain other makers) have a tarnished track record. Stick with first hand knowledge of what BM does or does not but more importantly, prove that it works. Bushmaster needs to build and maintain a good track record if they ever hope to gain the reputation as a maker of serious ARs
I have never double pressure-tested a bolt. Have you?
We fired 58 300 AAC BLACKOUT proof rounds on one of our bolts. They were about 75,000 psi. That bolt is now in my home defense rifle. I have absolutely no concern about it.
We fired 58 300 AAC BLACKOUT proof rounds on one of our bolts. They were about 75,000 psi. That bolt is now in my home defense rifle. I have absolutely no concern about it.
Don't worry, I'm concerned enough for the both of us... That's well beyond the rated life of a bolt.
We fired 58 300 AAC BLACKOUT proof rounds on one of our bolts. They were about 75,000 psi. That bolt is now in my home defense rifle. I have absolutely no concern about it.
Out of curiosity have you guys tested other bolts as well?
Well, I know the answer is yes, are you able to disclose the same data for the other bolts tested?
I have tested a lot of bolts. I had to pick which design to use for the AAC uppers. No, I can't compare them, but it was useful to make sure we got the best ones.
Mr. Silvers, BM has a long way to go before they establish themselves as a top quality manufacturer.
Hit the nail on the head.
As for the CMM cost comment: I don't see how any CMM sampling is 'inexpensive.' Even laser CMM's like the Faro and Nikon's I have worked with require a dedicated operator and some time for set-up. We would utilize them for developing our X bar and R charts, but 100% sampling is unheard of in high volume manufacturing. The best bet you would have is utilizing vision systems (i.e. a $18k Cognex camera), but even then you're looking at insane amounts of camera investment and requires the attention of a full time engineer. So you're stuck at batch sampling first and last offs if you're operation has it's **** together. Which if you're doing this and have a competent QC staff, you're on par with any 'world class manufacturer.'
Quality control isn't rocket science and I know any manufacturer is capable of it. That being said, I would only trust a manufacturer with a tainted track record if they would be transparent in their QC process. Specification control (finished material qualitites, dimensional), supply chain control (active inventory level management, quality of distribution).
I have tested a lot of bolts. I had to pick which design to use for the AAC uppers. No, I can't compare them, but it was useful to make sure we got the best ones.
Can't compare... Does that mean you cannot disclose results, or you did not directly compare them side by side and instead just grabbed desirable features?
...a lot of QC babble...
Forgot to mention: the most important part of a successful QC department is developing a relationship with a customer. We always hosted our major customers, showed them our processes, let them have input on what they thought was most important to them, then co-developed our processes and standards with them. That is the only way you're going to sell to your target customer. Now, it's up to your management when it comes to transparancy (how much you want to hate your life) of current production. In the end, your customer will see your product, it's just a question of how well you trust your personnel to react to situations that may be caught in the supply chain.
Bushmaster doesn't 'play the game' with m4c's community. That's what I saw before I purchased my Colt. And, in my opinion, m4c maintains it's credibility through it's moderators, ind. professionals and it's subject matter experts.
My apologies to all on this forum. I posted the following which is incorrect-
The proper way to verify torque is to set the torque wrench to the correct torque and tighten.
Total torque of the gas key bolts is 55 in/lbs + torque from staking. Specification for torque + staking is 55 in/lbs - 100 in/lbs. Verification would require setting the torque wrench to the nominal torque, which is halfway between minimum and maximum. That would be 77.5 in/lbs. Rounding up to 80 is acceptable. Apply 80 in/lbs of torque after staking to verify final torque.
After posting, I realized that re-torquing a staked bolt is an unacceptable procedure. One, there is a risk of compromising the mechanical lock feature of the stake. Two, if the staking is on the minimum side, it would be possible to over-torque the bolt. The proper way to check the torque of a staked bolt would be to break torque, then torque using the proper procedures. It's been a long week with too little sleep
Thank you and again, I apologize for any inconvenience this may have caused
Suwannee Tim
12-08-11, 17:43
....Simply claiming that it's believed a certain manufacture does or does not perform certain tests is not enough, especially if it is not first hand knowledge....
Folks who have absolutely no first hand information almost daily repeat the accusation that BM does not stake or does not properly stake their carrier keys.
Can't compare... Does that mean you cannot disclose results, or you did not directly compare them side by side and instead just grabbed desirable features?
I mean we tested many bolts to destruction, and I cannot disclose the results. But I used the information to select what bolt to use.
The military standard is that the stakes should not distort the side surfaces, and they should result in a removal torque no less than 55 and no more than 100 inch-lbs.
Granted, my 23&P only goes to C6 but how does one stake the sides of the key without distorting them? My book shows 35-40 in/lb.
In what spec is the 55-100 in/lb?
Granted, my 23&P only goes to C6 but how does one stake the sides of the key without distorting them? My book shows 35-40 in/lb.
In what spec is the 55-100 in/lb?
You can't distort the side bearing surfaces.
Near the top of the key it narrows and that's where the stake is.
Folks who have absolutely no first hand information almost daily repeat the accusation that BM does not stake or does not properly stake their carrier keys.
I can tell you that every time I go into a gun store or end up shooting with someone that has one, I look. I also look at their lack of staking on the receiver extension tube nut. Haven't seen one done correctly yet. Not once.
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