M16 FTF in FA help please

[troy28]

I am running an original M16 lower. It came as a burst from the factory but, has a Auto trigger. The BCG is a Y/M National Match M16. 30rd window Pmag. The upper is LMT MRP Gas with a 10.5in barrel.

I am running wolf .223 62gr FMJ. (Yes, dirty cheap ammo)

When running in FA randomly about once a clip it will stop firing. I typically try to only shoot ~3rounds by letting go of the trigger but, sometimes keep the trigger down to run out the mag.

When the gun stops firing I do not appear to have any jams. The bolt is closed and opens easily. When I pull the bolt back the round in the chamber is fully seated in the chamber and on the bolt. The round has a firing pin strike on the primer. The strike is deep enough in the primer that it is a defined circle with a little depth but the round did not fire.

I can take the rounds with the light primer strike and fire them in semi with no FTF. When I run in semi I do not get any FTF even if I pull the trigger as fast as I can. I tried multiple mags and meticulously cleaning the rifle same FTF in FA. When in FA it is never the 1st or 2nd round that is the FTF but any round after that appears to be possible anywhere from round 3 to round 30.

Unfortunately, I did not have another ammo to test with. But I would like to correct this issue so I can afford to still run in FA.

Any suggestions are greatly appreciated!

 

[Fargo]

Here is my take on it:

Sounds like a timing problem not uncommon with shorty AR's. The short gas system requires alot of gas and doesn't give the action alot of time to do its thing.

Basically, the short system is requiring your bolt to try to unlock before pressures have fully subsided. The case hasn't let go of the sides of the chamber yet and you are short stroking; not for lack of gas but because the gun is trying to extract while the case is still expanded in the chamber.

When you are running F/A, the problem is going to be worse because the gun is rushing things even more, especially if you haven't done anything to keep the cyclic rate down.

I have a friend whose 11.5 M16 does the exact same thing as soon as the suppressor goes on it. It becomes overgassed and tries to cycle too quickly.

If it is doing this with an A1/A2 stock, I don't know the fix as the rifle buffer is the most forgiving of the lot. If it is doing it with a telestock it is probably because you don't have a heavy enough buffer and/or stiff enough spring. A heavier buffer will slow down the entire unlocking/extraction process and bring your timing into sync as well as bringing your cyclic rate down a bit.

I've been told, but don't personally know, that an H2 or H3 buffer is necessary on a shorty gun like yours for consistent reliability.

Best,


Joe

 

[ryknoll3]

The heaviest buffer than will reliably run on the gun is best as it smooths things out a bit and makes the cycling a little easier on the parts. Try an H3.

 

[j706]

I am running an original M16 lower. It came as a burst from the factory but, has a Auto trigger. The BCG is a Y/M National Match M16. 30rd window Pmag. The upper is LMT MRP Gas with a 10.5in barrel.

I am running wolf .223 62gr FMJ. (Yes, dirty cheap ammo)

When running in FA randomly about once a clip it will stop firing. I typically try to only shoot ~3rounds by letting go of the trigger but, sometimes keep the trigger down to run out the mag.

When the gun stops firing I do not appear to have any jams. The bolt is closed and opens easily. When I pull the bolt back the round in the chamber is fully seated in the chamber and on the bolt. The round has a firing pin strike on the primer. The strike is deep enough in the primer that it is a defined circle with a little depth but the round did not fire.

I can take the rounds with the light primer strike and fire them in semi with no FTF. When I run in semi I do not get any FTF even if I pull the trigger as fast as I can. I tried multiple mags and meticulously cleaning the rifle same FTF in FA. When in FA it is never the 1st or 2nd round that is the FTF but any round after that appears to be possible anywhere from round 3 to round 30.

Unfortunately, I did not have another ammo to test with. But I would like to correct this issue so I can afford to still run in FA.

Any suggestions are greatly appreciated!

A common problem with short barreled full auto M16's. I ran into the same problem with my agency issued 11.5" M16A1. The hammer was actually following the round into the chamber at close to the same time. As a result the hammer did not have enough force to ignite the primer. I switched to a heavy buffer (H3) and a super strong buffer spring. I think the combination of the two slowed things down enough to make them work. Now it functions flawlessly. If you want to try one of the heavy springs PM me and I will be happy to loan you one.

 

[byggpoppa]

I never met an LMT that didn't prefer 5.56 atleast initially.

 

[yotewacker]

Mine use to do the same thing. I switched to a good quality factory ammo. No more problems.

 

[Fargo]

I still want to know what stock/buffer you are running.

Thanks,

Joe

 

[jeremy]

3 most common problems.
Gas tube fouled or damaged.
Extractor Fouled or damaged (to include Extractor Spring)
Mags

 

[Don]

When is the last time the hammer springs were changed?

 

[mammynun]

my first check would be for carbon buildup on the firing pin... my A1 was sensative to that, but it was 30 years ago. It's free...

 

[Longshot308]

The 3 rnd burst group in the weapon could be the issue. Since it is an original unit, some would not reset especially if you shot a 2 rnd burst. Have you switched the components or tried a standard M-16 trigger group?

 

[VUPDblue]

He already said that he has an auto only trigger group installed....

 

[alfahornet]

I am experiencing a near similar problem on my M16 with A1 stock. If I run it with an 20'' or 16'' upper it runs fine with all the buffers I have tried. Can do mag dumb every time with all the ammo I have tried (mostly Wolf, but some Fiochi, other brass, and other steel case russian) If I run it with a 14.5 or 11'' upper same or very similar problem happens. Adding a suppressor on the 14.5'' upper and it will run fine but without, the problem described by the OP occurs or in some cases the bolt doesn't go all the way forward but most often, the bolt is all the way forward and the round appears to be properly chambered. This usually happens after the 2nd or 3rd round.

With the 11'' upper depending on the buffer used it is semi only with the need to clear the chamber (ie. unfired round in it) after the first round fired nearly every time. I have experimented with 3 different buffers (original Colt A1 (20'' upper is original to gun), heavy buffer and pistol 9mm buffer) but none really worked reliably on the shorter uppers. Also the suppressor is not fixing the problem on the 11'' upper as it does with the 14.5. Certain configurations ammo, buffer make it worse but none I have tried have so far fixed the problem.

Any suggestions are appreciated. My research has mostly revealed 2 things, 1) heavier buffer should fix it or 2) have the gas ports on the uppers opened up a little bit more. I am little hesitant doing the latter as some people have told me that is not a 'good or proper' fix. Thank you for any suggestions.

Lower is a Colt factory M16A1. Uppers are Colt M4 uppers in 14.5 and 11''.

Works reliably in f/a with Colt M16 20'' upper, RRA 16'' 5.56 upper and 16'' RRA 9mm upper

 

[yotewacker]

I did drill my gas tube opening in the barrel 2thousounds over. I have a 10" barrel.

 

[jrainw]

I have worked through the same problem with my M16, after doing alot of research I found it was the bolt actually closing so fast that the carrier would bounce back at the moment the hammer was coming down on the firing pin causing the failure to get a good primer hit. Mine would do it with some mags and not other, what I found was any one of many parts can change the speed of the carrier when it is closing. New fire control springs because they help slow the carrier when it is coming back, heavier buffers or springs, good strong mag springs because the carrier drags across the next round to come out of the mag, or smaller gas ports because they delay bolt opening so the carrier moves slower. Try a H or H2 buffer with a new buffer spring and it will probably go away.

An extra thing I've found is a 9mm buffer will make this happen every round for me.

Hope this helped a little