I recently did a barrel swap on an XM177 clone, or maybe I should call it a parody. It's made by a defunct company from the late 70's that tried to make cheap rifles and subsequently went under. The binary trigger I dropped in is worth more than the rifle, but I digress.

The barrel was shot through, so I put a Luth-AR 10.5in barrel on with a traditional style sight/gas block (compatible with the thicker barrel diameter) and re-used the original gas tube.

Went to the range yesterday to put it through the paces and the first 10-15 rounds cycled without a hitch. Then I had my first FTE jam where the round was clear of the chamber but not ejected, jamming against the new round. Dropped mag, cleared jam, continued. After another 4-5 shots, I had another FTE. I changed mags and continued testing until the frequency of FTE's became every round.

I'll take the rifle apart tonight to try to figure out what's going on, but wanted to see if you folks have experience with this. If the buffer spring were the issue, the problem would have occurred right off the bat. Leads me to believe the problem is in the gas system. Heat related? Something came loose? I've never seen a clogged AR tube but maybe some crud got in there?