Originally Posted by
DireWolf
Assuming sending it back just isn't in the cards, 3 possible issues come to mind for troubleshooting:
1. Mag release button not screwed on far enough. This can cause a loose mag seating and cause the bolt to skip over the case head and grab forward on the case with the bolt lugs. Looks exactly like mark in pic when this happens.
2. Way over-gassed combined with either weak mag-springs or too much friction at feed ramp (can't really tell how smooth FR is from attached pic). What buffer weight does it have currently? Possible that too much gas-to-mass or too heavy buffer-spring may have the BCG cycling too quickly for the mag to raise the next round (e.g. if weak spring). May also potentially involve surface issues/debris on feed ramp, and the bolt lugs are skipping over the case head due to some impedence, and biting in further forward as the case moves up into-plane. Look to see if the case heads are getting chewed up...Possible tests would be new/alternate mag, increasing reciprocal mass, replacing buffer spring, and if necessary giving the ramps a bit of polish...
3. Debris in the buffer tube (or related) area which may be limiting rearward travel of the carrier. Does the carrier have full range of motion and are the spent cases ejecting?
ETA: If it either doesn't (or barely) eject a spent round, maybe it is in fact just short-stroking...can check the gas tube/block/key for possible issues or mosalignment, or possible bent firing pin restricting or seizing up travel of the bolt/cam in the carrier.