AR-10 ejection problem.

[dchan521]

Hi everyone,

I need some help with my AR-10 build regarding case not ejecting.
I have a Aluminum lower, and an Alexandria Profab upper that I bought complete. I used a regular cheap DPMS milspec LPK and buffer kit. I have a PRS stock also.
The upper is a 20in 1:10 twist wih a non adjustable mid gas length system.
I am shooting 147gr Magtech 7.62x51 ammo. The round is not ejecting after I shoot, but when I pull the bolt back it then pops out. It also pops out fine when I do not fire and just regularly cycle the rounds. I think I need a heavier buffer and a strknger buffer spring? What are you thoughts? Also, if I think I am right about the heavier buffer, what is a good recommendation for a heavier buffer and spring? Thanks.

[maxx03]

Sounds like there isn't enough gas thru the gas tube to push the bolt back far enough to cycle the firearm. Try checking for a loose or restricted gas block first.

[renardsubtil]

Ah the good ole ejection problems of AR10s...what a “fun” road. This post should’ve prolly gone in the semi auto forum but here’s some suggestions.

Basically and in layman’s term the case is getting stuck due to under OR an over gassed system. The main ways to balance out the movement of the ejected casing is to mess with the weight and the amount of gas used to move the bolt group.
You want to look at this chart from Slash’s heavy buffers (I am not associated with them) to get an idea of the weight buffer you need.
Then you want to buy an adjustable gas block so you can use any grain ammo. I like SLR rifle works’ selection.

Personally I had to use a heavy buffer plus an adjustable gas block for my 20” 1:11.25 twist build so be prepared to spend lots more money.

EDIT MAXX003 has the right idea too, before you buy stuff always check the easy stuff

[heyjerr]

Maybe check the gas rings on the bolt to make sure nothing is broken and that the gaps aren't aligned to allow leakage.
Also inspect the extractor for chips.

[ar15barrels]

I need some help with my AR-10 build regarding case not ejecting.
I have a Aluminum lower, and an Alexandria Profab upper that I bought complete. I used a regular cheap DPMS milspec LPK and buffer kit. I have a PRS stock also.
The upper is a 20in 1:10 twist wih a non adjustable mid gas length system.
I am shooting 147gr Magtech 7.62x51 ammo. The round is not ejecting after I shoot, but when I pull the bolt back it then pops out. It also pops out fine when I do not fire and just regularly cycle the rounds. I think I need a heavier buffer and a strknger buffer spring? What are you thoughts?

I think that a 20" 7.62x51 barrel should not have a midlength gas system.
Midlength is fine on a 16" barrel, but 18" and longer should have a rifle gas system.
A midlength gas system would create far too much dwell time which would definitely cause failures to extract/eject.

Either get an adjustable gas block or a new barrel and gas tube.
This is not something you can really fix with a heavier buffer.

[ar15barrels]

Sounds like there isn't enough gas thru the gas tube to push the bolt back far enough to cycle the firearm.

He likely has too much gas.
I can't imagine WHY any barrel maker would do a midlength gas system on a 20" 7.62x51 AR type barrel.

[dchan521]

Thank you all

[heyjerr]

Don't forget to update us when you find the problem :-)
Curious minds want to know!

[command_liner]

A few years back I bought from Midway an upper, an adjustable stock and an spring/buffer kit. The spring/buffer was mislabeled and it was the wrong length. The gun would fire, but not in any semi-auto mode, and would not do anything smoothly or well.

It is CERTAINLY POSSIBLE you have a combination of parts that is labeled incorrectly and will not work right. I spent a long time tracking down the problem and was pretty pissed when I found that Midway sent me mislabeled parts that could not be assembled into a functioning rifle.

[mitch1]

Check and see where the end of the gas tube is. It should be half way in the cutout of the upper receiver. I have seen a couple now that are short. The AR10 gas tube is 3/8" longer than the AR15 gas tube

[ar15barrels]

The AR10 gas tube is 3/8" longer than the AR15 gas tube

AR-10 gas tube is 3/16" longer, not 3/8".