Looking for AR builders, a little help please

[Cannonman]

I put a AR 10 in .308 together and it has feeding problems. Mostly it does not want to go into full battery. This upper does not have an assist. The first thing that came to mind was a buffer weight. Then, buffer spring, gas, bolt, ??? I have one other .308 and was thinking of changing out parts from the working model. The spring and weight seem the same. Not 100% sure of the spring. So, If you have an idea I love to hear it. Last, I never thought ammo would be a problem with a build. Or how to use the least amount of ammo to find the problem. I've re-loaded a fair amount of bottle neck cartridges but I fear I might be adding another unknown.

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[KG74]

start by swapping the uppers from lower to lower. Does the upper from the build in question go into full battery on the other lower? If so, you may have an out of spec buffer tube. That's a slight chance, I know but I've had it happen personally and diagnosed everything else first, but at least you should be able to narrow down 50% of the possibilities at that rate.

 

[Ops]

Ar10 buffer?

 

[matts]

Burr on the barrel or bolt?

 

[DirectDrive]

I'd use factory, full power 7.62 x 51 ammo for the break-in.

 

[dmack]

Are you using reloads? If the brass came from something with an oversized chamber, ie machine gun, and you don't use small base dies, the bottom of the brass may be bulged, not allowing it to fully chamber.

 

[Member 34319]

Too many variables and not a whole lot of given information to go off of, need more information to help.

Barrel, bolt, receiver brands. Ammo used. Lower, receiver extension size, buffer weight, spring, etc.

Could be as simple as reloaded ammo not liking the barrel. Or about 100 different things.

 

[Cannonman]

start by swapping the uppers from lower to lower. Does the upper from the build in question go into full battery on the other lower? If so, you may have an out of spec buffer tube. That's a slight chance, I know but I've had it happen personally and diagnosed everything else first, but at least you should be able to narrow down 50% of the possibilities at that rate.

Thx, I can try that.

 

[Cannonman]

Ar10 buffer?

yes

 

[Cannonman]

Burr on the barrel or bolt?

Yeah I wondered about that/. So I took a bolt from my Black Rain .308 and tried it. It gets stuck when you insert it in with the charging handle. You can not cycle the action.

 

[Cannonman]

I'd use factory, full power 7.62 x 51 ammo for the break-in.

It's a few different brands, American hunter was the last

 

[Cannonman]

Are you using reloads? If the brass came from something with an oversized chamber, ie machine gun, and you don't use small base dies, the bottom of the brass may be bulged, not allowing it to fully chamber.

Nope, Different factory loads. Same problems.

 

[WTC]

Yeah I wondered about that/. So I took a bolt from my Black Rain .308 and tried it. It gets stuck when you insert it in with the charging handle. You can not cycle the action.

Sounds like either the barrel lug or the receiver is out of spec if the 2ndd bcg doesn't work in the faulty upper

 

[DirectDrive]

Yeah I wondered about that/. So I took a bolt from my Black Rain .308 and tried it. It gets stuck when you insert it in with the charging handle. You can not cycle the action.

1) So you swapped in the B.R.O. BOLT only or the complete BCG (bolt carrier group) ?

Instead of waiting for your answer, I'll jump ahead.
One of the "things" that could be causing this, and it's not uncommon, is the gas tube/gas tube key alignment.
The portion of the gas tube that projects into the "carrier tunnel" has to align perfectly with the gas tube key on top of the CARRIER.
If it doesn't, this could very well be your issue.

The way to check this is to remove the BOLT from the CARRIER.
Then slide in the empty carrier in and verify alignment.
IF you have good alignment, then it could be an issue with the bolt/BE (barrel extension) interface.

As always, make sure that your bolt and bolt carrier group is assembled correctly.

From what you report, it sounds like gas tube alignment.
It's an easy fix.

 

[msgriff]

I assume that you're not riding the CH, but from you're brief description, I'm not sure I would let the BCG fly home as it may lock up. As posted above, any meaningful help is going to require more detail of your build list and function test. For my quick recommendation, unless you bought your bolt and barrel/extension as a matched set, I would start by checking headspace with the stripped bolt and the appropriate gauges. You may have a Armalite AR-10 cut chamber while using a DPMS spec bolt. You may also have the wrong gas tube, it should end at the center of the cam pin cut-out.

 

[Ops]

pull the gas block off with tube and see if the bolt goes all the way. what type of gas system you running?

 

[Member 18201]

There have been a lot of AR10 barrels on the market with incomplete finish reaming at the neck of the chamber.

Failure to completely chamber a round, as well as high pressure signs if the round did chamber.

I have had a few in the shop, all were stainless barrels, BTW.

 

[DirectDrive]

pull the gas block off with tube and see if the bolt goes all the way. what type of gas system you running?

No need to remove the gas key.
It could be staked, etc. etc. (leave it alone unless there is something clearly wrong with it)
Just check it like I outlined above.

 

[Ops]

might help if you read my post.

but im still waiting on type of gas system at least

 

[Cannonman]

pull the gas block off with tube and see if the bolt goes all the way. what type of gas system you running?

Thanks Ops! I will try this. It makes sense. Sorry about my ignorance, but what do you mean by "type" of gas system?