SBR malfunction

[themonk]

So I had the same issue with a very well known manufacturer and the issues turned out to be with the BCG, again for a tier one manufacturer. If you have an extra BCG I would throw it in and see if it runs before changing anything as you mentioned it used to run perfect.

[Tnemt]

Already tried another BCG. Runs the same

[Midwest Industries]

Do you live local to us by chance?

Thank, Peter

[P2000]

Windham 10.5 inch barrel. I was shooting a mix of ammo. UMC 55 grain fmj, hornady 55g, xm193, some handloads, all with the same outcome. It typically only happens when the gun gets hot or I fire at a faster rate.

Why would it begin after the fir initial 400-500 rounds? Up until then it ran like a top.

Typically a rifle's cyclic rate will increase slightly during the first few hundred rounds and also as the rifle gets hot. And mags get dirty/broken in as well which can slow down how fast the next round is presented. I bet your rifle was on the ragged edge to start with, because it's a 10.5 Windham(not the best) barrel, with carbine buffer. It isn't short stroking because it is locking back. The bolt is out running the magazine.
I'd get an h2 or even h3 from bcm, and order a bcm carbine spring while you are at it just to be sure.

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[Clint]

Typically a rifle's cyclic rate will increase slightly during the first few hundred rounds and also as the rifle gets hot. And mags get dirty/broken in as well which can slow down how fast the next round is presented. I bet your rifle was on the ragged edge to start with, because it's a 10.5 Windham(not the best) barrel, with carbine buffer. It isn't short stroking because it is locking back. The bolt is out running the magazine.
I'd get an h2 or even h3 from bcm, and order a bcm carbine spring while you are at it just to be sure.

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That's the most likely scenario.

Barrel with giant gas port and cheap CAR buffer = super high cyclic rate and intermittent reliability.

[MistWolf]

Locks Back + Failure to Eject + Failure to Feed = Extractor Problem.

Install an M4 extractor spring from Colt or Sprinco. Once the extraction issue is solved, you can address any over gassing issues, if they exist.

[P2000]

Locks Back + Failure to Eject + Failure to Feed = Extractor Problem.

Install an M4 extractor spring from Colt or Sprinco. Once the extraction issue is solved, you can address any over gassing issues, if they exist.

I agree with this too, except I would fix both issues at the same time(h3 buffer, bcm action spring, colt extractor and colt gold extractor spring)

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[markm]

Locks Back + Failure to Eject + Failure to Feed = Extractor Problem.

Install an M4 extractor spring from Colt or Sprinco. Once the extraction issue is solved, you can address any over gassing issues, if they exist.

I'm not a big fan of masking overgassing with a beefy extractor. I agree with installing a BCM extractor kit... that's never a bad idea. But no gun will run good with that useless car buffer. Especially a Windom (probably .080" ported) barrel.

In the dark ages, people put those o-rings in their guns. I guess none of us really knew better at the time. But now we know better. An SBR will never run good with a CAR buffer.

[Tnemt]

No. I live in tennessee

[MistWolf]

I'm not a big fan of masking overgassing with a beefy extractor. I agree with installing a BCM extractor kit... that's never a bad idea. But no gun will run good with that useless car buffer. Especially a Windom (probably .080" ported) barrel.

In the dark ages, people put those o-rings in their guns. I guess none of us really knew better at the time. But now we know better. An SBR will never run good with a CAR buffer.

Mark, I think your assessment that the barrel in question is likely over gassed is dead on. But fixing the extraction issue won't mask that. I can tell you from experience that fixing the over gassing first, will mask the extraction issue. The extractor of an over gassed AR will not lose control of the case rim unless the extractor is out of spec, or the spring is weak. A good extractor & spring will tear the case rim before letting it go.

Whether or not a short AR will run with a carbine weight buffer depends on gas port diameter. I haven't tried it, but I betcha with a small enough gas port, a shorty will run fine with a carbine buffer. I've tuned a suppressed 11.5 inch AR to run reliably and with soft recoil with an H buffer. I imagine I can do the same with a carbine buffer. However, I feel a carbine buffer is too light. Tuning an AR to a carbine buffer will give a narrower span of operation. I certainly wouldn't tune a full auto AR to a carbine buffer.

I have never used a BCM extractor spring. But I have seen posts where it turned out the BCM extractor spring weakened, causing malfunctions like the one we're discussing here. Those malfunctions were occurring with carriers with about 1000 rounds on them. Some were new carriers.

The O ring was a Crane fix because the M4 originally used M16 extractor springs which weren't up to the job. Colt redesigned the M4 extractor spring to eliminate the problem but the .gov was slow in adopting it it because they didn't want to introduce a new part number into the system. The Colt spring is designed to be used WITHOUT the O ring.

Every time I needed to trouble shoot an AR, it's always been a waste of time If I didn't eliminate any issues the BCG might have first thing.