7.62x39 AR upper with AA piston kit

[audet548]

Hi all,

I'm in the process of building an AR 7.62x39 upper with a Adams Arms piston kit. I started with the PSA 10,5" upper from irunguns, then installed the piston kit on it. My lower is a Core15 with a carbine standard buffer.

Before installing the piston kit, I shot the upper without any issue using chinese copper washed ammo.

On my first test fire with the piston kit, it was short stroking. The bolt was going back enough to eject the spent casing but not enough to pick up a new round. So I opened up the gas port to 0.125".

Second test fire, it was still short stroking but not as bad, on a 20 rounds try, it picked up a new round 2-3 times.

So what are your toughts? I'm thinking maybe the ammo I have doesn't have enough pressure, I had issue with it on a cz858 in the past failing to feed...

 

[yohann160]

Try removing the piston kit and going back to factory configuration. See if that works. If it does, use the piston kit as a paperweight or something. Those kits are a solution looking for a problem

 

[audet548]

Thanks yohann160, really helpful...

 

[TRG-42]

The AA kits are one of the better ones available . They are just not set up to run out of the box for 7.62x39

First is opening up gas port, which you did . I only had to go up to .116" BTW

Assuming gas regulator is in the 12 oclock position ( wide open ) , then check if you have the gas block spaced form the shoulder properly

Redo the process again if unsure . If you go to their FAQ and look at " Q. How do I know I spaced my gas block properly? " its pretty straight forward

You don't want too much gap ! I'm at .015" , which is the smallest the recommend

Biggest problem with 7.62x39 is the pressure between the various commercial ammo is all over the place !

Mine ran the old Norinco even at .100" gas port , but not the Wolf / Golden Tiger etc

I love this AA kit in 7.62x39 , since all the commercial ammo burns relatively dirty . My BCG has never been cleaned since !

 

[yohann160]

Thanks yohann160, really helpful...

You did admit in your OP that you turned a functional gun into a non-functional gun by adding unnecessary aftermarket parts to it. Solution is pretty obvious to me. If you absolutely need a piston you'd be better served with a factory built unit like PWS or something.

 

[John Deer]

Hi all,

I'm in the process of building an AR 7.62x39 upper with a Adams Arms piston kit. I started with the PSA 10,5" upper from irunguns, then installed the piston kit on it. My lower is a Core15 with a carbine standard buffer.

Before installing the piston kit, I shot the upper without any issue using chinese copper washed ammo.

On my first test fire with the piston kit, it was short stroking. The bolt was going back enough to eject the spent casing but not enough to pick up a new round. So I opened up the gas port to 0.125".

Second test fire, it was still short stroking but not as bad, on a 20 rounds try, it picked up a new round 2-3 times.

So what are your toughts? I'm thinking maybe the ammo I have doesn't have enough pressure, I had issue with it on a cz858 in the past failing to feed...

Do you really need the piston kit?

 

[audet548]

I don't absolutely need the piston kit, but you know, one of the pleasures of firearms is to modify them and trying new things... Of course I could leave it DI but what's the fun in it?

Anyway, helpful comments on trying to solve the issue is really appreciated, comments like "remove the piston and use it as a paper weight", not so much...if you don't want to help, please keep your comments for yourself.

 

[SteelCap]

Could very well be the ammo. Try other brands if that works.

 

[Deckard]

Maybe not enough powder is burnt by the time it hits the port. So faster burning powder?