Took this out recently from getting it back from the builder. Put a mag or two through it, zero malfunctions but extremely overgassed. Installed a KNS piston and took it back out yesterday. This kept happening while trying to adjust the piston. Seemed to do it with both a lot of gas, and with little gas. I believe i had more issues with a full mag than empty. I only brought 1 magazine and I am unsure if it's the same mag I originally had zero failures with.

You can see it picked up a new round which is nearly chambered, but the little edge on the front of the carrier has also picked up a round and ran it into the reciever. Attached File



Update post below

It's stripping 2 rounds meaning the magazine or rounds are sitting too high?

Might make sense why it's doing it with a full mag, all the pressure it pushing them up?

Lips are stretched/messed up?

Bet someone on here knows for sure, maybe they'll reply

I'd suspect the magazine. I'd try another mag first.

Is that a live round in the chamber or a spent round?

Live

Extractor condition?

Had this same malfunction multiple times with a proven reliable 556 AK.  Was 100% the magazine in that case.

What do you look for in the magazine that indicates stretched feed lips? Is there a measurement you need to verify or is it a visible sign? I have a bunch of surplus magazines and few have feeding issues at the end of the magazine and I would like to be able to check them. Could it be a mag spring issue, or just rough inside magazine finish/dirt?

In your case I would look at this first. As far as the other, visual inspection and you could measure/compare to known good magazines.

I was able to aquire 2 new production galil rock and lock mags. I shot a hundred rounds or so of some reman junk and had 0 malfunctions.

KNS piston tamed this beast beautifully

Glad you found your issue.  If I ever see this, I'll know what I am looking at.  Thank you.

A different mag may have fixed the symptom, but the root cause is a sharp edge or bur on your bolt.

See pic.  That corner edge needs a very slight radius on it to prevent it from dragging the #2 round forward.

Tony