AR short stroke issue!!

[DasSieben]

I bought 2 identical SOTA arms 7.62x39 uppers. I bought them to shoot surplus steel cased ammo.

1st upper had issues jamming below the feeding ramp. I ground out the feeding ramp and have had no other issues with it.

2nd upper didn't look like it was machined as well...had to drimel a dimple for dust cover to close and gas block was crooked. I went ahead and ground out the feeding ramps, and haven't had any jamming issues but first time out it short stroked every single round. Here's what I looked at:
-First I switched out a buffer spring and tube for lighter ones that I had on hand. It actually seemed to make a little difference...maybe only 70% failure instead of 100%.
-I swapped out BCG with my functioning upper. Didn't change anything.
-Removed gas block again...everything seems to aligned correctly now.

I'm not sure where to go from here, except maybe start cutting coils off buffer spring. Or call manufacture. In order to keep everything the same and figure out the issue, I'm using the same ammo and the same lower with both uppers. It's an Aero lower with a Spikes parts kit. Does anybody have any ideas? Thanks in advance!

 

[uncle money bags]

when you say short stroked; did the fired case extract and eject fine but the BCG did not pick up the next round in the magazine? And that the only change was the upper itself?
If so, then you have a gas issue. If by chance the round fired and the case was not extracted I can be virtually certain it is a gas leakage issue. Somewhere between the gas port on the barrel and the end of the gas tube where it mates to the gas key on the BCG you are leaking gas. Most likely the gas port on the gas block and barrel are not mated correctly. I wouldnt rule out one or the other being undersized or not drilled in the correct spot. Just a quick question: are the fired cases "hot" to the touch when they are ejected?

From what I am hearing you bought two uppers and neither one worked out of the box. The time to call the manufacturer or dealer who sold them is a little past due. Dont get me wrong, I am the same way. I would rather make it work if I can instead of getting it exchanged, but I wouldn't expect a lot of help from them. It wouldn't hurt to contact them anyway, you never know.

Sorry for the edits. I was writing between putting out "fires".

 

[Jwryan84]

Buy an AK to shoot 762x39, only ever here of issues in ARs

 

[Old Fart]

Buy an AK to shoot 762x39, only ever here of issues in ARs

This is what I keep telling myself. So far I don't have one.


Sent from Missile Silo 341A

 

[Preacherman]

I had this issue w/my first ar build. I put in a flat wire spring and it turned out to be 4" too long. I cut it and then I did not have any issues.

 

[doctorjj]

You lost me at "ground out the feeding ramp".

 

[SMS]

What length gas system and what buffer/spring combo are you using?

 

[mr ed]

before you start cutting springs, try going the other way with a H2 buffer and lube the crap out of it.

 

[MrShooter]

You lost me at "ground out the feeding ramp".

Same here.

 

[DasSieben]

Uncle Money Bags:
Thanks for the help! It extracted spent casing, but did not load a new one. But I didn't have a problem manually loading a new one. I didn't check to see if fired cases were hot to touch or not...but I'll check next time.

The only thing different about the 2 complete uppers is the style of gas block. The gas block seems to be mated correctly to the barrel, and I don't see any visible blow by around the port on the barrel where gas is leaking. The holes may not be correct size to be honest I'm not even sure what size they should be. I think I may swap the whole gas tube and block out with the upper that is working and see if that changes anything.

SMS:
I have a 16" 1:10 barrel with a 9 3/4" gas tube. The original buffer spring/tube were the UTG Pro. I don't know the exact spec, but I replaced them with a New Frontier Armory spring/tube. It was a visably lighter spring and about 3 coils shorter.