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captainbarred

7.62x39 question

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Hey guys,

 

Building a 7.62x39 Ar pistol upper and having some issues.

 

I built it using a Superlative arms piston kit.

 

I went with a 10.5in barrel with a carbine length gas system.

 

Superlative says the gas system should cycle perfectly fine with the 7.62x39 build.

 

With it wide open, it only extracts the shell casings about 3/4 of the way then stops(jams in place). I can grab the charging handle and easily finish the cycle to eject the spent round and chamber the next round.

 

Alignment of the gas block seems good, is it possible that the carbine length gas system, being so close to the end of the barrel is not creating enough back pressure before clearing the end of the barrel?

 

Anyone do a similar build? have similar issues?

 

Any ideas?

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I dont know but I would think the problem lies with the piston system. Either there is a gas loss or it isnt getting enough gas to operate completely. Maybe the piston rod isnt long enough? I am just throwing things out there and I think I would have tried a DI set up before going piston. All that said, I would clean it, well lubricate everything again and shoot it as is to see if it has to "wear in" a bit to be reliable. New builds can be finicky at times.

 

Good luck with it!

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Thanks for the input, I'll check out the link.

 

I ripped it apart last night to measure the gas port hole. its showing right about .091 which might be able to be opened to .093.

 

I might contact AR15barrels.com to see if he thinks it should be opened more.

 

gas block is adjustable, so I can always close it down more there.

 

I also need to check my buffer. Pretty sure I was running a carbine buffer, but might be an H... I'll check that...

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Have you tried loading 1 round in the mag?

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yessir.

 

next step is to polish the bore. run some brass casings. and possibly polish the chamber.

 

Also have some light weight buffers I can try.

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Try some brass ammo and see if it helps. We always hear to not use steel in an AR and I think this still holds true for 7.62X39. As I understand it, the steel ammo, especially lacquer coated. works fine with AK's because of looser tolerances..

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