Some notes. When failure to feeds/eject start happening one has to clean well the bolt, scrubbing all the carb/powder from the extractor and face. The ejector “finger” must be bent forward a bit and replaced at times since it is weak and when worn back even a little, the brass does not eject soon enough and the extractor goes into flip the brass out a bit too late and spins in the port over the magazine, staying in the gun.
The magazine must have a proper, touchy tension on the spring or the bolt literally reacts too quick for the mag to push the rnd up in time. That could be fixed by shortening the action springs but that would be just a band-aid fix to a festering problem. The bolt gets slightly rounded out where it contacts the magazine/round and if this is sloppy it slips sometimes.