I enjoy tinkering with mechanical things. That's why I've got a machine shop at home despite not being a mechinist for a living.

We took the carbines to an indoor range last night. It showed a couple failures to eject and failures to feed on each magazine fired. We swapped parts one at a time to see if it would help. We tried his bolt, recoil spring, guide rod, and magazines. It still exhibited the same issues.
When we got home I noticed that the gas cylinder was cracked on the bottom. It gave itself away by the gas residue on the gas cylinder. I notched the crack and welded it up with just enough heat for a good weld but without heating up the barrel. The welds were ground and polished without heating things up. After a thorough cleaning to get the metal, grinding, and polishing residue out of the carbine it was reassembled and put away for the night.

My shooting group had a range day this morning. I stopped in before work and ran a magazine full of Remington FMJ through the carbine. It had one bolt over base failure to feed on round 8 of 15.

When welding the gas cylinder I closed up about half of the vent. The piston is so chewed up that there is lots of extra gas getting around it. I hoped reducing the port would help put more gas on the piston and increase function. I can easily open it back up when the new piston and nut arrive.
Another thing that is rather annoying is the front sight is canted to the right. I can see that it's tight but not centered on the key. I'll knock the pin out and try lining it up better.

Again, I can futz around with this barrel's gas cylinder and not be too worried. I'm not weakening it structurally and if I can't get it to run I'll change the barrel. Unlike many butchers out there I have a clue what I'm messing with. My purpose in coming here was to find people that know more about carbines than I do. I don't have an ego and am not afraid to learn from others.

As it is, I'm having fun tinkering with the carbine. When I get it running I'll probably have to go back to wrenching on the hot rod to get my fix-it fix.