ar10 gas or buffer problem?

[Joe Blowitup]

I have an cmmg ar10 that has a problem picking up the next round and doesn't hold the bolt open on the last round. My question is about the buffer. The previous owner has put a magpul moe fixed stock on it. I'm not sure if he changed from a adjustable or fixed stock. At the moment it has a riffle buffer and I'm thinking it needs a carbine buffer since it has a 16 inch barrel. I have had this gun apart to check the gas system and gas rings and all seems good. Also can I use a ar15 carbine buffer or is the ar10 different. Thanks.

[HogKiller]

Been there seen that. Check the Gas Block for alignment. Make sure the whole thing is clear. I know you checked it but check it again. It sounds like either it's not getting enough gas or the spring/buffer is wrong.

[bender152]

When you manually pull the BCG back with the charging handle, will the bolt lock back?

I had a problem where I was running an A1 stock (which is similar in length to the Magpul fixed rifle stock), but the rear screw was too long and prevented the buffer from going all the way back, thus preventing the BCG from locking back on an empty mag. I had no problems cycling tho. A quick trim on the screw solved my problems.

[renardsubtil]

How many rounds have you shot through it? You should put at least a hundred or so rounds down range before modifying or buying new parts...if it's still new, oil the crap out of the bcg, they like to run wet for some reason.

If the problem still comes up after a hundred rounds, it could be a combination of a few things - report back with the weight of the buffer and check the spring size.

I had a similar issue with my last round not locking the bolt back and got myself a heavier buffer and longer spring and my issues went away. (For some off reason the A2 rifle spring I had was short and the buffer was 2 oz less than what's reported on the HeavyBuffer.com reference page)

[Joe Blowitup]

I'm almost sure the gas system is good and I even measured the gas hole in the barrel. It does lock back when I pull the charging handle and i have put about 200 rounds through it. I am the second or third owner an don't know when these parts were put on or round count.

[bender152]

Too many unknowns right now...

16" barrel. Is it carbine gas length?
Is the gas block adjustable?
You say it has a rifle buffer. Does that mean you're using an A1/A2 buffer tube?
Who makes the buffer and spring? Are specifically made for .308? Do you know the weight of the buffer?

The problem you describe makes it seem like it's under-gassed, but AR-308's usually have the opposite problem, being over-gassed.

If you're sure the gas system is good, then the issue might be with the spring and buffer.

[Joe Blowitup]

It appeared to be a riffle gas system with a 16 inch barrel. It has a a1/a2 buffer tube since it has the solid magpul fixed stock. It doesnt have an adjustable gas block. The only factory cmmg 16 inch 308 I have seen has been an adjustable buttstock so I'm thinking it had a shorter buffer when new. I guess I should call cmmg.

[bender152]

A 16" barrel with rifle length gas isn't a configuration I'm used to seeing, but CMMG does list it on their website.

Like you said, I would give them a call and see what they suggest regarding the buffer assembly.

[baih777]

Measure the length of the buffer and the spring and post the results.

[toddh]

It appeared to be a riffle gas system with a 16 inch barrel. It has a a1/a2 buffer tube since it has the solid magpul fixed stock. It doesnt have an adjustable gas block. The only factory cmmg 16 inch 308 I have seen has been an adjustable buttstock so I'm thinking it had a shorter buffer when new. I guess I should call cmmg.

Verify proper gas tube length.

Verify stroke length, and the bolt locks bag with empty mag.

Verify gas block alignment.

Verify buffer spring length, buffer weight.

Verify proper gas tube/key alignment.

.

[Nathan Krynn]

.308 AR's do not use the same buffers as AR-15's typically. Same tubes though. The buffers are shorter.

Also it makes no difference what so ever where the gas port is or barrel length for rifle or carbine buffer use. That is determined by the choice of buffer tube. You can have a different weight for the buffer per the amount of gas going back but the length is 100% up to the buffer tube.