308 AR-10 problem

Sharpeneddark · Dec 27, 2015

Hi guys. I have a PSA AR-10 that has a fairly frequent ejection problem. Like once every 7-8 rounds frequent. I am hoping this is something I can fix myself rather than get PSA involved. Here's a pic of what often happens. The case seems to stove pipe often. It's not always exactly like depicted, but this jam happens often just like this that. I've tried different mags (Magpul and steel mags) different buffer springs, and even have replaced the extractor. All the simple fixes I can think of I've tried. Any suggestions or should I just get PSA fix their crap?

Oh, I've tried various brands of ammo, including my own reloads. My reloads typically cycle better than the factory ammo. They jam once in 20 rounds vs once in 10 with the factory stuff.

iH8DemLibz · Dec 27, 2015

Is the BCG locking back every time when the last round is fired?

chevellenut71 · Dec 27, 2015

I had the same problem. What I found is the pmags are loose in mag well. Try using a steel mag. My problem went away with steel mag. Also if you put pressure on the mag by pulling back on it a little it goes away too. We did a video review on it. With further review to come. Just my opinion.

Sharpeneddark · Dec 27, 2015

I believe so. Now that I think of it, the bolt locks back and sometimes the last fired case is sitting on top of the mag follower, like it didn't even get thrown. Which is why I initially thought the extractor wasn't doing its job.

Sharpeneddark · Dec 27, 2015

chevellenut71 said:
I had the same problem. What I found is the pmags are loose in mag well. Try using a steel mag. My problem went away with steel mag. Also if you put pressure on the mag by pulling back on it a little it goes away too. We did a video review on it. With further review to come. Just my opinion.

I thought the PMag would be a problem, so I got a steel mag. The problem occurs with the steel mag, too, just maybe not as often.

iH8DemLibz · Dec 27, 2015

The BCG isn't staying rearward long enough for the empty case to clear the ejection port.

It's short stroking. And capturing the case as the BCG is moving forward.

Sharpeneddark · Dec 27, 2015

iH8DemLibz said:
The BCG isn't staying rearward long enough for the empty case to clear the ejection port.

So perhaps a different buffer/spring combo may be the trick? I changed the spring once before, but it was one of those $3 things off of Midway saying "We see you are looking at 308 stuff...want this?" ideas. Perhaps a flat wire spring and a non PSA buffer?

Vile Shadow · Dec 27, 2015

iH8DemLibz said:
The BCG isn't staying rearward long enough for the empty case to clear the ejection port.

It's short stroking. And capturing the case as the BCG is moving forward.

Buffer spring too heavy?

Or undergassed?

iH8DemLibz · Dec 27, 2015

I would put all stock parts back in and try it. Standard weight buffer and standard weight spring.

If it doesn't work that way, lube the hell out of her and try again. If it doesn't work that way, then I would say she's under gassed.

I will let others chime in on swapping buffers and springs.

I like setting mine up so they're gassed properly to operate with stock parts and the least powerful ammo I have. Makes life much easier.

OP, any tightness or binding with the stripped BCG sliding back and forth in the upper?

Sharpeneddark · Dec 27, 2015

Thanks for the help. The rifle has always had this problem with all stock parts. I initially wrote it off thinking it was bad ammo. Changing ammo types then parts was an attempt to rectify the issue before getting PSA involved. Looks like I may just do that after all.

clandestine · Dec 27, 2015

Sharpeneddark said:
I believe so. Now that I think of it, the bolt locks back and sometimes the last fired case is sitting on top of the mag follower, like it didn't even get thrown. Which is why I initially thought the extractor wasn't doing its job.

This is often an overgassing issue. You need a really heavy buffer or adjustable gas.

IMO, from your description its NOT undergassed.

I have seen this countless times, especially with .308 based ARs.

iH8DemLibz · Dec 27, 2015

clandestine said:
This is often an overgassing issue. You need a really heavy buffer or adjustable gas.

Not arguing here.

Can you explain the mechanics/timing of over gassing so folks understand?

Sharpeneddark · Dec 27, 2015

clandestine said:
This is often an overgassing issue. You need a really heavy buffer or adjustable gas.

IMO, from your description its NOT undergassed.

I have seen this countless times, especially with .308 based ARs.

Thanks! Do you have any suggestions on replacement parts? I'm considering replacing the gas block, anyhow, but didn't want to until I had this ejection problem sorted.

clandestine · Dec 27, 2015

iH8DemLibz said:
Not arguing here.

Can you explain the mechanics/timing of over gassing so folks understand?

Overgassing will often present itself in many ways (oversize gas port). Sometimes a gun with a short throat leade will show signs of overgassing when it is not overgassing.

-Stuck Casings in the Chamber
-Empty Casings still in the gun facing the shooter or laying on top of the Mag Follower and sometimes stovepipes
-Pressure Signs on the back of the Casing (Ejector Imprint, Popped Primers, Flattened Primers, or Extractor Claw Distortion)

Undergassing will present itself in many ways. Sometimes its not really undergassed due to small Gas Port. It can be a misaligned Gas Block/FSB, worn Gas Tube Flange, Gas Key oversized or leaking, bad Gas Rings, Heavy Buffers/Action Springs. An undergassed AR will often eject as the round is shorter after the projectile is fired.

-Wont lock bolt back on the last round
-Fires a round but wont strip a fresh one off the magazine or half feeds a round from the magazine and dents the casing with the Bilt Lugs

clandestine · Dec 27, 2015

Sharpeneddark said:
Thanks! Do you have any suggestions on replacement parts? I'm considering replacing the gas block, anyhow, but didn't want to until I had this ejection problem sorted.

SLR click adjustable Gas Block. Its the only ones I have found to be repeatable (changung ammo changes the settings), and reliable.

Have you checked to see if your buffer is the proper length. .308 ARs use different length buffers.

iH8DemLibz · Dec 27, 2015

clandestine said:
Overgassing will often present itself in many ways (oversize gas port). Sometimes a gun with a short throat leade will show signs of overgassing when it is not overgassing.

-Stuck Casings in the Chamber
-Empty Casings still in the gun facing the shooter or laying on top of the Mag Follower and sometimes stovepipes
-Pressure Signs on the back of the Casing (Ejector Imprint, Popped Primers, Flattened Primers, or Extractor Claw Distortion)

Undergassing will present itself in many ways. Sometimes its not really undergassed due to small Gas Port. It can be a misaligned Gas Block/FSB, worn Gas Tube Flange, Gas Key oversized or leaking, bad Gas Rings, Heavy Buffers/Action Springs. An undergassed AR will often eject as the round is shorter after the projectile is fired.

-Wont lock bolt back on the last round
-Fires a round but wont strip a fresh one off the magazine or half feeds a round from the magazine and dents the casing with the Bilt Lugs

Preciate it.

Sharpeneddark · Dec 27, 2015

clandestine said:
SLR click adjustable Gas Block. Its the only ones I have found to be repeatable (changung ammo changes the settings), and reliable.

Have you checked to see if your buffer is the proper length. .308 ARs use different length buffers.

The buffer device doesn't appear to be any different than a standard AR-15 buffer, outside of being a little thicker. My 308 buffer has a little "H" on it and seems to weigh a slight bit more, but I have no scale to verify weight. The tube on the 308 appears to be longer, as there is a gap in between the castle nut and the collapsible stock. Attached pics show the 308 on the left and two 223 buffers on the right with their respective springs.

Edit: I measured my buffer tubes between the AR-15 and AR-10. The AR-10 is about 1/2 inch longer. I measured from the sling plate. The AR-15 was 7" and the AR-10 was 7 1/2"

clandestine · Dec 27, 2015

Sharpeneddark said:
The buffer device doesn't appear to be any different than a standard AR-15 buffer, outside of being a little thicker. My 308 buffer has a little "H" on it and seems to weigh a slight bit more, but I have no scale to verify weight. The tube on the 308 appears to be longer, as there is a gap in between the castle nut and the collapsible stock. Attached pics show the 308 on the left and two 223 buffers on the right with their respective springs.

Edit: I measured my buffer tubes between the AR-15 and AR-10. The AR-10 is about 1/2 inch longer. I measured from the sling plate. The AR-15 was 7" and the AR-10 was 7 1/2"

What I was getting to was bolt travel. A buffer that is too long wont allow for proper function.

If a .308 bolt travels too far rearward the fat portion will wedge itself into the buffer tube, if the buffer is too long there will be insufficient bolt travel for reliable function and if too little, wont allow the bolt to lock back.

Last trip to delmarva I helped a gun who had a custom .308 AR (Built by a "gunsmith") that had a buffer too long that wouldn't allow the bolt to come back far enough to lock the bolt catch open.

There is no "standard" for .308 AR's and everyone does something a little different, it makes troubleshooting a little more difficult.

Can you take a picture of the buffer tube opening?

The easy way to test for proper bolt travel is to part the upper and lower

Next, take the bolt group out of the upper and make sure the buffer and spring is installed.

Then manually push the bolt into the buffer tube as when the gun is cycling. The fat part of the Carrier should not make contact with the lower or the buffer tube AND the bolt should clear the bolt catch by at least 1/4".

clandestine · Dec 27, 2015

Your ejector could be messed up too. can you take a picture of the bolt face? If you rock an empty casing in the bolt face does the ejector have good tension?

Sharpeneddark · Dec 27, 2015

I took the lower off and put the BCG against the buffer and compressed it as far as I could. There is about a 1/8-1/4 inch gap between the fat part and the buffer tower. I attempted a pic. I also took a pic of the opening.

308 AR-10 problem

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