Originally Posted by
a308garand
Start with the least expensive fix and try your rifle:
1-Try a known good quality bolt carrier. If your rifle starts running, you know the gas key is not sealed anymore,,,time to replace the gas key and stake it in place.
next-if #1 didn't help
2-Try a replacement gas tube with your original bolt carrier. The old tube may have a build up of residue from the 22 conversion that has not been blown clear by shooting .223. The old tube may have been twisted or damaged somehow to become slightly misalligned and not allow enough gas flow.
next-if #1 or #2 didn't work
3-The old standby, check your bolt gas rings. They my be worn down and leaking. Replace them with a brand new set. Test your set up again.
Wild hunch and remote possibility,,,if the upper receiver is slightly out of spec, receiver that was mismachined and not allowing the magazine (feelips bottoming out too soon) to sit tall enough to function right....maybe it was ok for a while before being broken in and now caused trouble?
I am leaning towards the gas leakage being the trouble....gas key, gas tube, bolt rings or a combination of all.