7.62x39 10 inch barrel, help

[Bahick71]

I have a bca 7.62x39 upper with.a 10 inch barrel, with a pistol length gas system.
I inherited this from my son. He shot it for a little bit and broke the.extractor
He got another complete bcg from bca. With new bolt he had problems with extraction.
He got fed up and gave it to me with a fired case stuck in the chamber.
I got the case out.and.cleaned, it was very dirty. I found it had a small burr starting into the chamber
I gently removed the burr and tried it at the range.
It will pull the spent case out but does not eject it, and it tries to pick up the next round and double stacks
The spent round and the next round.
I tore it back down and checked the gas system, looks all good. I think I may have a combination of problems
I am thinking it may have a bent pin on the extracter, It will not come out easy. I need to try and get it out
With a hammer and punch. Any other ideas, I though at first or might need a heavier buffer,, but if the bolt
Is not coming all the way back I may be wrong, or is it moving too fast? I am running a standard carbine buffer
Any insight would be greatly appreciated.

 

[undeg01]

I would say if it is not ejecting the spent case, I would not change the buffer just yet. And if you do, you probably need a lighter buffer or a lighter buffer spring.

If you have a round chambered and jerk the charging handle all the way back, will it properly eject the cartridge? if so, then I’d lean toward the spring or buffer issue. I have experienced something similar and simply cut one coil off the spring.

Does it have an adjustable gas block? If so, make sure that is opened up all the way and see if that makes a difference. Whether it has an adjustable gas block or standard, make sure the gas block is properly aligned with the gas port.

If it is properly aligned, then you might need to drill the gas port slightly larger. I had a 300 BLK pistol that exhibited similar symptoms and I ended up drilling the gas port out to 1/8”. That is oversized for a gas port but ultimately that is what it took to fix my problems.

 

[Bocephus123]

I would say if it is not ejecting the spent case, I would not change the buffer just yet. And if you do, you probably need a lighter buffer or a lighter buffer spring.

If you have a round chambered and jerk the charging handle all the way back, will it properly eject the cartridge? if so, then I’d lean toward the spring or buffer issue. I have experienced something similar and simply cut one coil off the spring.

Does it have an adjustable gas block? If so, make sure that is opened up all the way and see if that makes a difference. Whether it has an adjustable gas block or standard, make sure the gas block is properly aligned with the gas port.

If it is properly aligned, then you might need to drill the gas port slightly larger. I had a 300 BLK pistol that exhibited similar symptoms and I ended up drilling the gas port out to 1/8”. That is oversized for a gas port but ultimately that is what it took to fix my problems.

That's how we learn! my 350 legend AR hasn't jammed once since i figured the real problem out... after a good while ill let everyone make their own opinion.!

 

[joegrizzy]

I have a bca 7.62x39 upper with.a 10 inch barrel, with a pistol length gas system.
I inherited this from my son. He shot it for a little bit and broke the.extractor
He got another complete bcg from bca. With new bolt he had problems with extraction.
He got fed up and gave it to me with a fired case stuck in the chamber.
I got the case out.and.cleaned, it was very dirty. I found it had a small burr starting into the chamber
I gently removed the burr and tried it at the range.
It will pull the spent case out but does not eject it, and it tries to pick up the next round and double stacks
The spent round and the next round.
I tore it back down and checked the gas system, looks all good. I think I may have a combination of problems
I am thinking it may have a bent pin on the extracter, It will not come out easy. I need to try and get it out
With a hammer and punch. Any other ideas, I though at first or might need a heavier buffer,, but if the bolt
Is not coming all the way back I may be wrong, or is it moving too fast? I am running a standard carbine buffer
Any insight would be greatly appreciated.

i've dealt with getting a 7.62x39 short barrel upper to run. there's a good bit of info you can find about the manufacturing of the bolt itself, but mostly from what i can recall the gist is:

>earlier model used a 5.56 bolt and just milled the face to accept the 7.62x39 case, which has a thicker rim than 5.56.
>the shaving of the bolt face led to the lugs on the bolt receiving a different amount of force due to different dimensions from the alterations to the bolt face.
>this would lead to situations wherein lugs would dig/drag/wear, carrier tilt could occur, you can find reports on forums of ALL sorts of "maybe it's this, look at this" type posts
>in later models that were made with dedicated bolts, this issue supposedly doesn't present itself as much

i'll link just a *few* posts that came up when searching today, i *know* i've read several of these when i had issues.

Do the 7.62x39 AR15's have bolt head issues? [Archive] - 6.5 Grendel Forum : : For the 6.5 Grendel Aficionado

Why has the 6.5 Grendel bolt head been improved and the 7.62x39 still uses the original design? Is there some reason the improvement is not needed for the Russian round?

www.65grendel.com

7.62x39 AR Issue

Hey all, I recently put together a 7.62x39 AR-15 and I'm have extraction/cycling issues with it. The rifle has a 20 inch barrel with rifle length gas port with an Adams Arms piston system and BCG. The gun fires fine, but is not cycling. I initially thought I might have a misaligned gas...

www.northwestfirearms.com

https://www.theakforum.net/threads/7-62x39-ar-15-build-questions.314499/

after doing LOTS of autismo research, what i *personally* think is causing this issue for MOST people is simply a gas issue.

while i agree about the bolt issues, and trying to source who *actually* made the one you are looking at can be trite, from my personal situation, i cogged it something like this:

>trigger pulled
>firing pin hit primer
>bullet go bang
>sometimes the bolt wouldn't even go back, or if it did, imperceptibly
>bullet definitely exited
>spent case seems "stuck" (this is because the force of the bullet going boom usually cycles and extracts for you; extracting a spent round manually is usually "harder" in most guns due to the case being swollen and is just a weird phenomenon thing; it's not really harder to extract than it would normally be. usually when something is amiss, people start being "careful" and being "careful" and then trying to say manipulate a charging handle to eject a spent case that has swelled a bit after firing you probably aren't going to be using your normal amount of dummy force, so you'll think it's "harder" or "stuck" because you aren't just he-manning it like usual)
>get case out, looks fine
>load another round
>pull trigger
>firing pin hit primer
>bullet go bang
>same thing
>bullet must be exiting barrel before enough gas gets thru gas system to force open bolt and force ejector to function
>gas taking path of least resistance and following the barrel after the bullet exits

might not be the most "suggested" solution, but i widened my gas port by drilling it out a teeeeny bit and it literally made ALL the difference in the world. i think the whole thing is a gas issue that leads to other problems because their isn't enough force in the system to really function it properly and stuff doesn't move like it should, resulting in odd hang-ups or unusual wear patterns/dragging.

you can test this by using a suppressor or even a fake one. any long enough muzzle device would test this because then the gas wouldn't escape *quite* as quickly and more of it should theoretically go thru the gas port and thus cycle the rifle properly. many people in many posts reported their firearms working fine with a can or long brake, but not without. this was because it's a gas issue.

too long; didn't read: not enough gas going thru gas port before bullet leaves barrel. make gas port wider for more gas, rifle functions.

 

[Bahick71]

Thanks guys
My son was running the upper on a different lower.
It functions properly pulling the charging handle back, cycles fine
I do have a couple different springs and buffers I can try.
The complete upper is all bca parts, and the bcg he bought was bca as well
The gas block is not adjustable, I am pretty sure the gas hole is larger than normal
I will.have to go check the specs
Thanks again for.the input, kinda sends me where I was thinking

 

[joegrizzy]

Thanks guys
My son was running the upper on a different lower.
It functions properly pulling the charging handle back, cycles fine
I do have a couple different springs and buffers I can try.
The complete upper is all bca parts, and the bcg he bought was bca as well
The gas block is not adjustable, I am pretty sure the gas hole is larger than normal
I will.have to go check the specs
Thanks again for.the input, kinda sends me where I was thinking

even if larger than normal, 1/8'' seems to be the sweet spot. it's *probably* not that big.

 

[Bahick71]

Bca says the gas port is .093 so definitely smaller than 1/8

 

[Bahick71]

Update
I tore everything down
Found that the pin in the bolt for the extractor was deformed
I had to drill half the pin out. Repaired that with a new pin
Installed a new adjustable gas block
Finally got to the range, fired and adjusted the gas block
Had to tune the gas block a couple times, runs like a champ now
Brass throw is good. Throws it just about even with my right shoulder
Thanks for all of the input and help

 

[mouthpiece]

I did not read the whole thread.
I have several of these in 7.62x39 and they run flawlessly but you need to know what to look for to get them to run reliably.

1, First thing is you need to slow down the extraction.
use the heaviest buffer that will run with your ammo Or you will continue to break extractors. You have to allow the gas pressure to drop before trying to yank the case out of the chamber.
2, 2nd thing that may help is to regulate or restrict gas at the gasblock If the heavier buffer doesn't help.

Are you using a FA(full auto) carrier? It is a bit heavier than a semi carrier and helps slow down extraction.
can you hand cycle ammo with/by the charge handle? If so, it is possibly just too much chamber pressure before unlocking.

 

[08H3]

Buddy of mine got a 10.5 350 legend BCA upper, biggest pos ever. We tried everything to get it to run and oycle target ammo but it wouldn’t. We opened up the gas port to just under 1/8” and it still wouldn’t run so it went away.