AR Pistol Diagnostics - failures to eject

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CE310QT

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I’ve looked for a sticky. I’ve searched the threads trying not to be redundant. Ive got a problem that is somewhat unique from what I can tell.

10.5” AR pistol
Carbine length gas system
Pistol buffer tube and spring
H2 buffer
Various magazines

In the last few rounds of ANY given magazine, I get failures to eject. Baffles me.
It DOES lock back on empty.
When it cycles properly, it calmly ejects at about 3:00-4:00 about 6 feet away. Makes me think it MIGHT be underpasses.

This is a new problem. Has several thousand rounds through it. And it runs like a top until the mag is almost empty.
 
If it locks back on empty, it isn't a gas problem. What make of pistol is it? After several thousand rounds, your extractor and ejector may need some attention.

What do you mean by failure to eject. Is it pulling the brass out of the chamber? If not, I'd look at the extractor and check the spring tension. Are you running an o-ring under the extractor? Is it pulling the brass and not kicking them out? If so, check out the ejector.
 
I have an AR pistol with the same barrel length, gas system, etc. but a heavier buffer. If you are actually getting problems related to extraction, it could be because of premature opening of the bolt when residual pressure is too high. My gun is ridiculously over gassed. I have a 6.2 oz. buffer and added about 4 oz. of weights to the BCG. It now functions in what I think is a correct manner.
 
CE310QT said:
In the last few rounds of ANY given magazine, I get failures to eject. Baffles me.
It DOES lock back on empty.
When it cycles properly, it calmly ejects at about 3:00-4:00 about 6 feet away.
Click to expand...
Clarification.

-It locks back on its own firing the last round? Then the bolt is at least cycling back; might be weak but it's not shortstroking.

-When it fails to eject, where is the unejected brass left?
 
Have you done a really detailed clean? I'd take the bolt apart and get every bit of crud out of it. Clean the chamber really well, and give a good quality lube on all the wear surfaces. Also clean out the gas tube and the gas hole in your barrel.

If that has been done or doesn't work, then check extractor and ejector.
 
Really no need to even clean the gas tube especially if it locks the bolt back on an empty magazine. I suggest cleaning really good AND checking your extractor and extractor spring.

In fact there is no real reason to ever clean the gas tube under normal use. Most civilian (and military) shooters will never need to clean a gas tube.
 
What does the brass look like? Pictures of the cases and rims would help diagnose the issue.
 
If your AR is giving you trouble because it's dirty, there's something wrong with it. ARs don't need to be cleaned, they need to be lubed. If it was a gas problem or a buffer problem it wouldn't wait until you're almost done with the magazine. My bet is on the extractor and/or ejector. Inspect them for wear/breakage. If they look good, replace the springs. Really, you should have spares of the extractor and ejector anyway. I keep all of the parts necessary to rebuild the bolt in my grip.
 
check gas block key. if the screws weren't staked properly they could loosen and allow gas to escape from the bolt.
 
JERRY said:
check gas block key. if the screws weren't staked properly they could loosen and allow gas to escape from the bolt.
Click to expand...

It isn't likely that the key is only leaking for the last few rounds of the magazine. Besides, he said it'll still lock open on the last round. If it locks open, but isn't kicking the brass out, it's gonna be either the ejector or extractor. Can't be more specific without more details.
 
JERRY said:
check gas block key. if the screws weren't staked properly they could loosen and allow gas to escape from the bolt.
Click to expand...

Seeing your post kinda made me laugh. Remember ten years ago when all the rage was whether your carrier's key bolts were "properly" staked? I was imagining vendors all over the world going out into their shops with a hammer and chisel.
 
TonyAngel said:
...Are you running an o-ring under the extractor?
Click to expand...
Do not use an o-ring. If the extractor needs an o-ring, the spring needs to be replaced.

CE310QT, your AR is showing classic symptoms of a failing extractor spring. Replace it with either a Colt or Sprinco M4 spring.
 
MistWolf said:
Do not use an o-ring. If the extractor needs an o-ring, the spring needs to be replaced.

CE310QT, your AR is showing classic symptoms of a failing extractor spring. Replace it with either a Colt or Sprinco M4 spring.
Click to expand...

Primary Arms has 5 coil springco springs in stock.
 
This will be easier to figure out once he answers the lockback question. Duh he answered it, never mind.:oops:
 
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