AR pistol teething problems -- suggestions needed

[Whisper]

I'm hoping some of you AR pistol builders can help me with a problem I am having.

I've built two AR rifles with no trouble, and they function well.  My latest build is an AR pistol in .300 AAC Blackout.  It's giving me trouble.

The gun will not extract a fired case about 75-80% of the time.  The round fires, the bolt comes back leaving the case in the chamber, and when the bolt goes forward it pushes the next round into the rear of the case still in the chamber.   Sometimes, not always, when I drop the bolt on a fired case in the chamber, I can pull the bolt back and it will extract the round.  When that doesn't work, just the slightest tap with a cleaning round stuck down the barrel will always dislodge the case, so it's not like the cases are tightly stuck in the chamber.

This happens with both supersonic and subsonic rounds, in light and heavy weights.

My first thought was that the extractor spring might be weak or otherwise defective, so I replaced it with a new Colt copper-colored extractor spring, reportedly the best one going.  It made no difference.  

My next idea has been to try adding one of those silicon doughnuts to the extractor to see if that helps.  But it's also occurred to me that perhaps the extractor itself is to blame. Maybe a badly shaped tip?  Or perhaps it's something else.

Any suggestions from AR builders familiar with this issue will be appreciated.

Thanks,
Whisper

 

 

[ehull20000]

If you can swap another extractor in there that sounds like an easy step in troubleshooting.  

 

Does the fired brass have any unusual marks on it?  

[Whisper]

Brass looks normal, with no unusual marks.

[ehull20000]

If you have another bolt or extractor I would swap that in there and see what happens.  

 

Also, does a different type of ammo make any difference?

[Whisper]

Type of ammo makes no difference -- I've used Remington, SiG, Freedom.

I'm not going to swap used bolts between rifles, but the idea of temporarily borrowing the extractor from another AR is worth pursuing.  It would confirm if the extractor is the problem.  Thanks.

Anything else I should investigate?

[jonnnyboy]

Since the bcg is the same between 556 and 300blk, I would pull a bcg out of a working gun and try it in the pistol.  This will give you some idea of which parts are being problematic.  I'm betting a new extractor will be your answer. 

PSA AR15 Extractor - 1346

$13.99 in stock at Palmetto State Armory

[Oh Shoot]

Assuming the extractor itself is in spec (it probably is) this has worked for a lot of folks with short-barreled ARs:

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm-exspring-1.htm

But it's mainly just the stiffer spring, o-ring seldom needed. You can get an o-ring at hardware store, it's a # 60, and you can get a stiffer spring elsewhere too. But a convenient way to get it all in one kit.

- OS

Edited July 24, 2016 by Oh Shoot

[rugerla1]

6 minutes ago, Oh Shoot said:

Assuming the extractor itself is in spec (it probably is) this has worked for a lot of folks with short-barreled ARs:

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm-exspring-1.htm

But it's mainly just the stiffer spring, o-ring seldom needed. You can get an o-ring at hardware store, it's a # 60, and you can get a stiffer spring elsewhere too. But a convenient way to get it all in one kit.

- OS

This fixed my issue when I had the same problem as OP. I ordered the 3 pack just in case it ever came up on another rifle. Great kit!

Edited July 24, 2016 by rugerla1

[KKing]

First off, what gas length is your barrel? It's possible you're so over gassed that the bolt is being pushed away with so much force the extractor can't grab, no mater what spring is in there. I'd do the BCM upgrade regardless, just because to me it's cheap insurance. Otherwise, if you're over gassed you need an adjustable gas block. Don't even fiddle with heavier buffers, springs, etc.


Sent from my iPhone using Tapatalk

[Oh Shoot]

16 minutes ago, KKing said:

First off, what gas length is your barrel? It's possible you're so over gassed that the bolt is being pushed away with so much force the extractor can't grab, no mater what spring is in there. I'd do the BCM upgrade regardless, just because to me it's cheap insurance. Otherwise, if you're over gassed you need an adjustable gas block. Don't even fiddle with heavier buffers, springs, etc.


Sent from my iPhone using Tapatalk

Yeah, it's admittedly somewhat of a kludge if you really want to optimize the system. But does seem to be fairly permanent one.

- OS

Edited July 24, 2016 by Oh Shoot

[tmauto769]

3 hours ago, KKing said:

First off, what gas length is your barrel? It's possible you're so over gassed that the bolt is being pushed away with so much force the extractor can't grab, no mater what spring is in there. I'd do the BCM upgrade regardless, just because to me it's cheap insurance. Otherwise, if you're over gassed you need an adjustable gas block. Don't even fiddle with heavier buffers, springs, etc.


Sent from my iPhone using Tapatalk

I am thinking it is in the gas system as well. I had an adams arms .308 that was piston driven that would do the exact same thing as the op described. I solved mine by drilling the gas port in the barrel. After that, it ran like a champ. fwiw, I wouldn't hesitate to swap a bcg or even just the bolt itself from another working rifle to troubleshoot something, done it a few times with no problems.

[Whisper]

Thanks, all.  The gun is a 10.5-in, and the opinion on the .300 Blackout forum seems to be that it can't be overgassed.  I'm going to try an extractor replacement and running it extra wet and see what that does.  Won't get to shoot it again until Saturday but I will report on my findings.

Thanks again,
Whisper

[MuscleHead]

12 hours ago, Whisper said:

I'm hoping some of you AR pistol builders can help me with a problem I am having.

I've built two AR rifles with no trouble, and they function well.  My latest build is an AR pistol in .300 AAC Blackout.  It's giving me trouble.

The gun will not extract a fired case about 75-80% of the time.  The round fires, the bolt comes back leaving the case in the chamber, and when the bolt goes forward it pushes the next round into the rear of the case still in the chamber.   Sometimes, not always, when I drop the bolt on a fired case in the chamber, I can pull the bolt back and it will extract the round.  When that doesn't work, just the slightest tap with a cleaning round stuck down the barrel will always dislodge the case, so it's not like the cases are tightly stuck in the chamber.

This happens with both supersonic and subsonic rounds, in light and heavy weights.

My first thought was that the extractor spring might be weak or otherwise defective, so I replaced it with a new Colt copper-colored extractor spring, reportedly the best one going.  It made no difference.  

My next idea has been to try adding one of those silicon doughnuts to the extractor to see if that helps.  But it's also occurred to me that perhaps the extractor itself is to blame. Maybe a badly shaped tip?  Or perhaps it's something else.

Any suggestions from AR builders familiar with this issue will be appreciated.

Thanks,
Whisper

 

 

If you home the bolt on an empty non ejected case and its not extracting manually its one of two things really. Extractor issues or a tight chamber. If it was a tight chamber you would probably have a mark on the rim of the casing from the extractor. But if you have been trying to troubleshoot it alot and not paying attention to the casing your extractor could already be damaged. I would pull and inspect it closely. Pull one from a good rifle if your not sure what to look for.

 

What brand bolt are you using?

 

Also what buffer spring/ buffer are you using? Is the spring used by chance?

 

 

[Whisper]

Project update:  I installed a brand new Colt extractor and heavily oiled the bolt.  The gun no longer leaves cases in the chamber but still does not fully extract or eject them most of the time.  

This time I had with me another shooter with a 10.5-in .300 pistol (different mfg than mine, but also with gas port at the pistol position).  We compared our fired brass and it does appear that the brass from my gun is slightly more scratched up -- not seriously, at least to my eyes, but it's clear his chamber is smoother.  

We swapped uppers on our two pistols, and with his upper, my pistol worked flawlessly with supersonic and subsonic ammo -- Barnes, Remington, and SiG. I think it's clear there is no problem with the buffer or spring; the problem is in the upper.

My thought now is that the chamber wasn't properly cut and may need to be finish reamed again, or perhaps buffed out somehow.  Maybe I should get in there with a Dremel and some Flitz?  Your theories are welcome.

Thanks,

Whisper

 

 

 

Edited July 31, 2016 by Whisper

[Omega]

You mentioned a new extractor but not if it came with the o-ring kit.  Some 300 BOs need a little extra grip for some reason, if you didn't install one you may want to try it before doing any lapping of the chamber.