View Full Version : M-16 Help light primer strike = Shortstoke?
Dock Rocker
08-23-10, 21:03
Ok here goes. I have a lower that we manufactured. Used the bowers jig to locate the sear hole, and everything is in spec on the lower. We have a weird situation. I think that it may be shortstroking. There is one more weird thing. I have a stock Rock River upper and when you put the M16 bolt it will fire 2 or 3 times then it quits. There is a live round in the chamber with a dent in the primer. I swap to another upper and it does the same thing. When I swap to a friends delton upper. Same length (16in) same M-16 bolt it runs like a sewing machine. I have now tried a heavier spring and a heavier buffer and neither changed anything. When I put the gun back to stock, slap on the delton upper it just runs.
Why the heck would it run with one with one lower and not another all else being the same?
Does anyone have any idea what the heck is going on????
Let me make sure I understand this. You have a lower receiver that you converted to full auto by installing an auto sear. Is that correct?
Ok here goes. I have a lower that we manufactured. Used the bowers jig to locate the sear hole, and everything is in spec on the lower. We have a weird situation. I think that it may be shortstroking. There is one more weird thing. I have a stock Rock River upper and when you put the M16 bolt it will fire 2 or 3 times then it quits. There is a live round in the chamber with a dent in the primer. I swap to another upper and it does the same thing. When I swap to a friends delton upper. Same length (16in) same M-16 bolt it runs like a sewing machine. I have now tried a heavier spring and a heavier buffer and neither changed anything. When I put the gun back to stock, slap on the delton upper it just runs.
Why the heck would it run with one with one lower and not another all else being the same?
Does anyone have any idea what the heck is going on????
Dock Rocker
08-23-10, 21:13
Let me make sure I understand this. You have a lower receiver that you converted to full auto by installing an auto sear. Is that correct?
Sorry, Yes I am on 07 FFL and have payed my SOT. This is a post sample gun. We have all of the documentation to do this.
Ok, let's dig a little deeper.
1. What type of ammo are you using?
2. What position is the hammer in when the live round is still in the chamber? Is the hammer forward or is it cocked?
3. Exactly what type of buffers have you tried? I am sure that you are aware of the different types- carbine, H, H2, H3, 9mm carbine.
My first instinct is that you may be having a bolt bounce issue.
I want to understand correctly that the Del-ton upper in its' configuration is working properly?
Bolt Bounce or Hammer Follow from a slightly miss drilled auto sear.
Can you list the parts and manufacturers in the combo's that work and do not work.
Dock Rocker
08-24-10, 06:43
1. What type of ammo are you using?I have tried everything from handloads, wolf to Remington. Same thing dosent work with my two uppers and does with the Del-ton. All of the ammo works like a champ in semi but will not work on full
2. What position is the hammer in when the live round is still in the chamber? Is the hammer forward or is it cocked? I will have to check. I have been ejecting the shell before breaking the gun apart. I will take a look this afternoon.
3. Exactly what type of buffers have you tried? I am sure that you are aware of the different types- carbine, H, H2, H3, 9mm carbine. Yes all I have on hand are the standard carbine buffer that came with the gun, a H2, and a hydraulic buffer. The symptoms do not change when the buffers are changed. Not sure how it would react to a 9mm.
My first instinct is that you may be having a bolt bounce issue.
I want to understand correctly that the Del-ton upper in its' configuration is working properly? Correct. The Del-ton upper is also a 16, M4 profile just like the other two uppers. I can feed it any ammo available and it runs without a problem. I have put a mic on every part I can mic with out completely disassembling his gun. Everything seems the same as the other two uppers.
Since this started I have put new gas tubes on both of my uppers and checked the gas system thoroughly. I mic'ed the gas port in my barrel and it was .062. My friend was not to keen on me pulling off the gas block to mic the delton gas port.
Thank you for the help
Dock Rocker
08-24-10, 06:52
Bolt Bounce or Hammer Follow from a slightly miss drilled auto sear.
Can you list the parts and manufacturers in the combo's that work and do not work.
The constant here is a Del Ton lower that I used a bowers jig to drill the sear pin hole. It has a M-16 parts group and all uppers were tested with the same bolt.
Upper 1: Factory rock river upper 16 in barrel M4 feedramp, carbine length gas tube, Works fine in Semi no full.
Upper 2 Factory CMMG upper same specs as Upper one. Works on Semi and no full
Upper 3 Factory Del-ton upper 16 in barrel M4 cuts, and when put on the same lower it runs great. We put 100 rounds of different ammo through it last night and it did not fail to fire any of them.
I think my buddy has put some sort of Voo Doo Hex on my uppers.
Don't pull the gas block's
Load one round and fire it, see if the bolt carrier locks back on the bolt catch.
As for if the hammer is dropped or not, do not dissassemble the gun with alive round in it. Just swtich the selector to semi, if the hammer is still cocked you can hear the auto sear let it go to the disconnector, and then you can fire the round in semi, if the hammer has already fallen you can't do this.
Dock Rocker
08-25-10, 17:25
Load one round and fire it, see if the bolt carrier locks back on the bolt catch.
I did this with several brands of ammo and each time the carrier locked back. I did it both suppressed and unsuppressed and it worked every time.
As for if the hammer is dropped or not, do not dissassemble the gun with alive round in it. Just swtich the selector to semi, if the hammer is still cocked you can hear the auto sear let it go to the disconnector, and then you can fire the round in semi, if the hammer has already fallen you can't do this.
I did this and the same thing happened every time with every ammo. The gun went through about 10 rounds just fine on full auto and the stopped. I flipped over to semi, and nothing happened. The hammer had already fallen.
Any Ideas what to do next? Is this bolt bounce?
I experienced this exact thing in Iraq with our Bushmasters. A live round in the chamber and the hammer was forward. I ended up rebarreling the weapon which solved the problem.
Prior to that I replaced every part in the lower, the buffer and the buffer spring and nothing would fix it.
If you have a bore scope I would scope the gas port and see what it looks like. If it is elongated/ oval then I would say that it is toast.
Disclaimer- "This statement has not been evaluated by the FDA for its' content or accuracy. Always consult a professional for a real evaluation".
Load one round and fire it, see if the bolt carrier locks back on the bolt catch.
I did this with several brands of ammo and each time the carrier locked back. I did it both suppressed and unsuppressed and it worked every time.
As for if the hammer is dropped or not, do not dissassemble the gun with alive round in it. Just swtich the selector to semi, if the hammer is still cocked you can hear the auto sear let it go to the disconnector, and then you can fire the round in semi, if the hammer has already fallen you can't do this.
I did this and the same thing happened every time with every ammo. The gun went through about 10 rounds just fine on full auto and the stopped. I flipped over to semi, and nothing happened. The hammer had already fallen.
Any Ideas what to do next? Is this bolt bounce?
Dock Rocker
08-26-10, 09:05
Iraqgunz, I am going to pull the two problem uppers apart tonight and check the gas port. I am going to check them using progressively larger drill bits (not drilling just using them for size). If they are not perfectly round do you think it would hurt to try to drill the hole out to the next larger bit size? If the barrel is trashed already I might as well try something.
Bolt bounce or a slightly mistimed autosear drill position - or carrier not quite to spec and trips earlier than it should.
Given it is erratic performance, I would guess bolt bounce.
Try a heavier buffer.
If your gas port is starting to errode, if you drill it bigger it will just make your gun run that much faster, creating more bolt bounce issues, you can attempt a heavier buffer band aid.
Another issue is your rounds could be hanging slightly up on the feedramps and slowing bolt lock enough that the hammer falls before the bolt is locked.
None of the three brands of upper you have is what I would recommend for a select fire gun.
Ok, I think your problem is an incorrectly timed sear. Its not bolt bounce or any thing else assuming you have a rear full auto buffer with sliding weight mass. The sear drilling hole jigs are not very accurate compared to centering the tool on the selector and then off setting the sear hole the correct distance above the it.
Wrote this years ago and it was on Quaterbore's web page for a while.
I wrote this up for RDIAS but it works for RR guns too. You have to bend the auto sear to retime it if it is out.
To check the timing is easy, to adjust the timing is hard.
With a M16 or AR15 with M16 parts and the DIAS in place...
1) Remove any magazine and ammo from the gun.
2) Set the selector on the full auto position.
3) Drop the hammer with the trigger (you did check to see the chamber was empty right?)
4) Now you need your timing gauges ( The cheapest is drill shanks at the required dimensions. I use three, one early timing gauge
.12 dia, one correctly timed gauge .10 dia, and one late timed gauge .08 dia.)
5) Secure the trigger in the fired condition (rearward) with wire. Using the charging handle pull the bolt carrier all the way to the
rear but do not let it go, slowly lower the carrier towards the front until you have a 1/2" gap left between the carrier and barrel
extension.
6) Insert the early timed gauge in between the bolt carrier and the barrel extension (not the bolt head) and slowly lower the bolt
carrier with the charging handle. If the auto sear releases then your gun is out of time (early) and will most likely give you light
primer hits. If not go to step 7.
7) Slightly retract the charging handle and remove the early gauge and insert the late gauge. Slowly lower the carrier until the
carrier rest on the gauge that is between the bolt carrier and the barrel extension. The hammer should have dropped, if it did not
the gun is out of time (late) and will most likely either not release the hammer or act sluggish and have a slow cyclic rate. If it
dropped go to step 8.
8) Pull back on the charging handle and recock the gun while removing the late gauge. slowly lower the bolt carrier with the "go"
or correctly timed gauge until the bolt carrier rest on the gage that is against the barrel extension. It might release or might not.
I use this gauge when tuning a M16's timing. I set the timing so the hammer falls with this gauge but not the early gauge.
Assuming that the hammer was released on this gauge but not the early gauge the gun is timed.
Now that you have determined the timing of the gun you must adjust it. the DIAS should NOT be loose in the gun since it can
shift and effect your timing. The easiest way to secure it in the gun is to A) drill a hole and tap it in the auto sear body so you
can clamp it to the upper lug and adjust the timing with shims on the front side or 2) You can (like me) glue plastic shims to the
upper lug with JB weld so the DIAS is timed to each upper by the shims on that lug. Moving the sear forward in the gun makes
the timing later (therefore correcting an early timed sear) and rearward makes the timing earlier (correcting a late timed sear).
As far as I know (someone can correct me) the erosion can only be seen by scoping the barrel from the inise, not from the top as you are suggesting. I know that we used a scope to make the determination. I also agree with Kevin. None of the uppers you are using would be something that I would want on a full auto lower.
Iraqgunz, I am going to pull the two problem uppers apart tonight and check the gas port. I am going to check them using progressively larger drill bits (not drilling just using them for size). If they are not perfectly round do you think it would hurt to try to drill the hole out to the next larger bit size? If the barrel is trashed already I might as well try something.
You say you "think" it is an incorrect sear, gotcha. but, to say that it is not bolt bounce or anything else is simply wrong. Especially because what he is describing is exactly what happens when you have a bolt bounce issue.
Not saying that you are wrong or right. Just saying that at this point you have to explore all the options.
Ok, I think your problem is an incorrectly timed sear. Its not bolt bounce or any thing else assuming you have a rear full auto buffer with sliding weight mass. The sear drilling hole jigs are not very accurate compared to centering the tool on the selector and then off setting the sear hole the correct distance above the it.
Wrote this years ago and it was on Quaterbore's web page for a while.
I wrote this up for RDIAS but it works for RR guns too. You have to bend the auto sear to retime it if it is out.
To check the timing is easy, to adjust the timing is hard.
With a M16 or AR15 with M16 parts and the DIAS in place...
1) Remove any magazine and ammo from the gun.
2) Set the selector on the full auto position.
3) Drop the hammer with the trigger (you did check to see the chamber was empty right?)
4) Now you need your timing gauges ( The cheapest is drill shanks at the required dimensions. I use three, one early timing gauge
.12 dia, one correctly timed gauge .10 dia, and one late timed gauge .08 dia.)
5) Secure the trigger in the fired condition (rearward) with wire. Using the charging handle pull the bolt carrier all the way to the
rear but do not let it go, slowly lower the carrier towards the front until you have a 1/2" gap left between the carrier and barrel
extension.
6) Insert the early timed gauge in between the bolt carrier and the barrel extension (not the bolt head) and slowly lower the bolt
carrier with the charging handle. If the auto sear releases then your gun is out of time (early) and will most likely give you light
primer hits. If not go to step 7.
7) Slightly retract the charging handle and remove the early gauge and insert the late gauge. Slowly lower the carrier until the
carrier rest on the gauge that is between the bolt carrier and the barrel extension. The hammer should have dropped, if it did not
the gun is out of time (late) and will most likely either not release the hammer or act sluggish and have a slow cyclic rate. If it
dropped go to step 8.
8) Pull back on the charging handle and recock the gun while removing the late gauge. slowly lower the bolt carrier with the "go"
or correctly timed gauge until the bolt carrier rest on the gage that is against the barrel extension. It might release or might not.
I use this gauge when tuning a M16's timing. I set the timing so the hammer falls with this gauge but not the early gauge.
Assuming that the hammer was released on this gauge but not the early gauge the gun is timed.
Now that you have determined the timing of the gun you must adjust it. the DIAS should NOT be loose in the gun since it can
shift and effect your timing. The easiest way to secure it in the gun is to A) drill a hole and tap it in the auto sear body so you
can clamp it to the upper lug and adjust the timing with shims on the front side or 2) You can (like me) glue plastic shims to the
upper lug with JB weld so the DIAS is timed to each upper by the shims on that lug. Moving the sear forward in the gun makes
the timing later (therefore correcting an early timed sear) and rearward makes the timing earlier (correcting a late timed sear).
Thomas M-4
08-26-10, 19:54
As far as I know (someone can correct me) the erosion can only be seen by scoping the barrel from the inise, not from the top as you are suggesting. I know that we used a scope to make the determination. I also agree with Kevin. None of the uppers you are using would be something that I would want on a full auto lower.
Iraqgunz there is a pic some were on the net that shows sectioned barrel showing the gas port erosion. And you are correct the erosion makes the gas port shaped like a funnel bigger diameter in the bore.
Its been a couple of years since I have seen maybe somebody know were it is and post it.
You say you "think" it is an incorrect sear, gotcha. but, to say that it is not bolt bounce or anything else is simply wrong. Especially because what he is describing is exactly what happens when you have a bolt bounce issue.
Not saying that you are wrong or right. Just saying that at this point you have to explore all the options.
Bolt bounce and incorrect timing will give the same issues. If he has a standard M16 internals and not shooting a odd set up of parts they should work and not be a bolt bounce issue.
Correct, if the auto sear trips before the bolt is closed you get the same result: Live round in the chamber, hammer down. He also had the issue with an H2 buffer that makes bolt bounce less likely.
Until he said that one upper runs fine, I suspected the incorrect auto sear issue.
Since one works and two don't I'm going to go with bolt bounce.
If he knew carrier velocity we could run that in or out as well. But unless you have highspeed video and cutaway upper and buffer tube its hard to do.
Get a Colt or LMT upper and see what happens...
Dock Rocker
08-27-10, 21:03
I am working on getting a colt upper right now. I am just going to slap a new colt upper on and see what happens. I have also ordered a slew of buffers to try. I hope to work through all this week after next. Thanks for all the help guys.
Do you have any new info for us?
I am working on getting a colt upper right now. I am just going to slap a new colt upper on and see what happens. I have also ordered a slew of buffers to try. I hope to work through all this week after next. Thanks for all the help guys.
Heavy Metal
09-04-10, 12:47
Iraqgunz, I am going to pull the two problem uppers apart tonight and check the gas port. I am going to check them using progressively larger drill bits (not drilling just using them for size). If they are not perfectly round do you think it would hurt to try to drill the hole out to the next larger bit size? If the barrel is trashed already I might as well try something.
You can't check them from the top. The hole size on the outside will remain the same. It will erode where it contacts the barrel and elongate towards the muzzle becoming a 'funnel'.
Dock Rocker
09-17-10, 07:14
Do you have any new info for us?
I have some great news. The first thing is I now have enough spare parts to build another gun. I bought everything I thought I would need, and started replacing things one at a time. I wanted to be somewhat methodical about it so I could really figure out what was happening. When it was all said and done Iraqgunz was right on target. I swapped a H2 buffer in and it ran much better but not perfect. Last night I put in a H3 and now it runs like a champ! The gun in its original configuration with the H3 buffer runs like a champ. Again now I have a good running lower and a pile of parts for a new gun!
Thanks much Iraqgunz and your advice!
carshooter
09-17-10, 10:41
I have also run into this exact issue with several commercial uppers on Registered Receiver lowers.
I guess it shouldn't be surprising, since it's a known issue that some commercial uppers are severely overgassed.
Switching to progressively heavier buffers until the Bolt Bounce issue stops has always cured it for me also.
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