No mention of rimmed or rimless, but rimmed cases will catch on the cartridge cutoff sometimes. Could be anything. The gap on the claw of the extractor to the bolt face to shallow. The extractor spring too strong. Wrong rotor. You did not say if the bolt was sliding over the cartridge. Could be your bolt stop is too long and the bolt is not getting behind the cartridge. Could be a couple little things put together. It is really hard to tell without looking at it. If you reload, load up some EMPTY dummy rounds and try to see what is going on when you cycle it.
