I'm a little stumped on this one. Maybe telling the story out loud will help me land on the issue, or maybe one of you will figure it out first.

I inherited a CAR15 clone with a 10.5 barrel, a worn out barrel, and a Sendra (crap) lower without a buffer detent. Hey, I like a project. Let's have some fun.

I put a Franklin binary trigger on it, because I also inherited 1000rnds of 55gr ammo and why the heck not. The barrel is 5.56 and the ammo is .223. No issue in this direction (though very bad if a reversed scenario).

Since the barrel was shot out and keyholing everything at any range, I replaced it about a year later with a Luth-Ar 10.5 barrel with at 1:9 twist.

Right away, accuracy was awesome. The rifle fired 8 rounds, and then encountered a failure to eject. The case was extracted, but evidently not far enough to spit out the side of the gun, and jammed against the round trying to feed into the chamber. I fired 3 more, and then another FTE. After this point, all rounds would not eject.

Thinking I had a clog, i took the rifle home and cleaned it. No luck

Maybe the rifle was under gassed (but why did it work to start with...), so I tried a lighter buffer spring. No luck

Thinking the original gas tube was the issue, I replaced it. No luck.

The owner of my local gun shop shined a bore scope in it and verified that my gas tube is properly aligned. "Not perfect," he said, "but it should be fine." He installed a buffer detent.

None of this has worked. The bolt "stands on its own" when doing the gas ring check. I don't see obvious signs of gas leaks. The case will extract if I manually pull the bolt back.

Why is my gun not cycling? More puzzling, why did it work at first and then not. As if something clogged (but nothing has) or something wore out (I can't find what).