Help me with my AR problem...

[pklin1297]

Hello all,

So I took my first AR (built entirely by me) out to the range yesterday for its first shoot, and after getting so many jams, the only way to make the gun work was shooting one-shot at a time. I was reading on AR15.com and the situation I encountered was very similar to what they called "short stroking". I have included a few pictures to illustrate what I kept encounting:


Condition of brass after jams because the bolt group does not move far enough back to catch the end of the round.


Last round hold open position for my AR, which is too far forward the the bolt catch is catching on the space between the bolt and the carrier.


Last round hold open position that is normal. Bolt catch is catching the front of the bolt


The typical jam I get every magazine.

The rounds eject perfectly every time, but the bolt group does not move back enough to chamber another round, or catches the round in the wrong place to cause the jam. What are some fixes for this?

If I were to have someone rebuild this gun for me, who do you guys recommend? Thanks.

[blkA4alb]

First of all, lube. Proper lubrication solves the majority of gun problems.

Second, what ammo are you using?

[ocabj]

When I've had this problem on an AW, I would just switch to a different mag because the problem has always been the magazine itself. I'd take it apart clean it, and if it still persisted with that mag, I'd change out the spring.

Obviously, this is more of a hassle to test out with an OLL since you have to pull the pistol grip off before you can swap mags (legally, at least).

I'd go with the easy tests firsts, which were mentioned by blkA4alb. Clean the bolt and bolt carrier then relube with CLP or Militec (I prefer Militec). If it still persists, try different ammo, preferably NATO pressure loads. If it still persists, then go with a different mag.

Best case, it's just your rifle being too 'virgin' with commercial/SAAMI spec loads. If this is the case, the NATO loads should help break it in.

[pklin1297]

I used both Black Hills Blue Box 55 grain and also Winchester 55 grain.

The barrel is a mid-gas position, I am also using a M16 heavy bolt carrier group from LMT that the key is pretty solidly staked, and also a regular weight CAR buffer with Chromium-silicon CAR spring.

[cho034442]

Do you have the same problem when cycling the rounds manually? If not, the problem could be with the barrel's gas port is too small or there is gas leak from the gas tube.

[pklin1297]

I will check the mag also since the spring tension felt a little weak to me, but it was a brand new C-Products 10 rounder with Chrome Silicon spring also with a Magpul follower and L-plate.

[TMC]

I used both Black Hills Blue Box 55 grain and also Winchester 55 grain.

The barrel is a mid-gas position, I am also using a M16 heavy bolt carrier group from LMT that the key is pretty solidly staked, and also a regular weight CAR buffer with Chromium-silicon CAR spring.

Is that the buffer than the upper maker recommends? If not I'd try a standard buffer.

I've also seen the firing pin hang up on the hammer on the return stroke. Make sure the front edge of the firing pin head that rests against the carrier doesn't have a sharp edge.

Good luck

[grammaton76]

Occasionally, the barrel's gas port will be incorrectly drilled and either not aligned with the gas tube, or there'll be a flake of metal left over from the drilling process that ends up blocking off your gas tube.

I had a Stag Limited upper that this happened with (not sure which it was, but it was something along those lines), but CWS got it shipped off to Stag, then returned, and it's worked fine ever since.

[dw1784]

Do you have the same problem when cycling the rounds manually? If not, the problem could be with the barrel's gas port is too small or there is gas leak from the gas tube.

+1. Chk the tube/gas key alignment and fit. Gas key and tube should mate with a slight thumb preasure instead of a slip fit. Pic 2295 only happens when a round is fired/ejected? if it's manually cycled then mag/bolt catch functions normally(2296)?

Nice gun btw. Good luck

[bwiese]

Lube, lube, lube. Use BreakFree CLP.

Use your chamber brush to scrub the chamber too.

Exercise the extractor & ejector a hundred times or so (on your well-lubed bolt) while you watch TV.

The ammo you used should work OK with a heavier M16 carrier.

Make sure nothing's dragging on the mag lips.

[pklin1297]

+1. Chk the tube/gas key alignment and fit. Gas key and tube should mate with a slight thumb preasure instead of a slip fit. Pic 2295 only happens when a round is fired/ejected? if it's manually cycled then mag/bolt catch functions normally(2296)?

Nice gun btw. Good luck

I'll check the mating of the key and tube tonight...

If manually operated the bolt catch and bolt group functions fine.

I've heard from AR15.com that the chrome silicon spring in the receiver extension might also be the problem since it has 10% more power than a regular spring, which might not allow the bolt group to go back far enough under the same amount of pressure. I will replace with regular spring and see what happens.

I lube always with CLP.

[pklin1297]

Is that the buffer than the upper maker recommends? If not I'd try a standard buffer.

I've also seen the firing pin hang up on the hammer on the return stroke. Make sure the front edge of the firing pin head that rests against the carrier doesn't have a sharp edge.

Good luck

Upper maker? I didn't buy it from a maker... I built it up piece by piece myself. The buffer is what is meant for the CAR receiver extension.

[pklin1297]

Bump

[cornholio1]

Do you nearby friends have an AR that you could use parts from for a trial and error?

Do you have anymore mags to try? Try bushmaster mags first. Then I'd replace the bolt carrier group parts.

[pklin1297]

I am using the Magpul CTR stock, with regular-weight carbine buffer and now regular spring (was using chrome silicon spring before which is longer and extra powered). At the range I was shooting Black Hills Blue Box 55 grain and Winchester White Box 55 grain and both returned the same results.
I just got another 10 rounder from C-Products and I also have a Bushmaster 10 rounder I can try, and I will definitely try them soon, after checking everything else to make sure function is correct.
After speaking to Randall from AR15barrels.com, he brought to my attention that the short stroking may be caused by the tan paint on the inside of the upper receiver, since he had seen this same scenario before, and it was solved either by wearing down the paint, or the removal of paint. It was also noted that I probably did not use enough CLP or lube on the parts, which would be correct since I used it sparringly. I thought I had read somewhere that too much lube in certain areas is a big no-no, so I was being careful.
I will try to remove the paint on the inside of the receiver and apply more lube and see if that will do the trick. Will report here of the result after test firing it again either Sunday or sometime next week.

Thanks all.