Headspace could be a problem and can be checked with a closed bolt up through magwell with some quality feeler guages. I believe most were in the .003-.004" range for a good to go gap. Replacing the roller locks is easy enough to tighten things up as long as there wasn't too much monkeying that happened to it.
Trunnions were welded in improperly also to the receivers as well as many receivers were twisted during welding causing interesting problems. SS receivers tended to be better than steel ones.
That said I had several with no ill affects and still have one that runs like a champ.
You also need to check chamber for burs as it was fluted to help ejection, burrs can stop ejection.
Check the ejector also. spring could be worn or broken. These were parts guns and all old crusty parts were reused.
Check gas port and piston function also. Port might be partially blocked. Pistons were canted or rubbed pretty bad on some. Also due to poor welding of receivers to tubes.
Test with snap caps or dummy rounds.