Either the mag not retained in the mag well correctly, such as the mag catch assembly correctly threaded into the mag catch button so the threaded section of the catch is flush with the face of the button.

Mag catch slot milled too low in the receiver so the mag is not held up high enough, or the mag well too over sized milled/you using the mag for a hand grab, both of which can cause the front of the mag to angle downward to cause too steep of an attack angle for the round to feed correctly.

Radius edge on the barrel feeding breach face not rounded enough, and can cause this edge to bite into the case to cause bind denting.

Short stroke, or case over at cycle to cause the bolt to try to force the round out of the mag via the middle of the round, instead of the round being pushed out of the round from behind the rim.


If you want to give us more details, we can narrow the problem down more specify, then just chucking lawn darts blindly  as the list above.

Shove the mag button in all the way with a pencil, reach over to the other side of the receiver, and crank the mag catch assembly out to remove it from the receiver.

Now with the mag button/spring removed as well, dry fit the mag catch to receiver to make sure that there is no debris/burs in the receiver mag catch channel that is preventing it from seating/ engaging the mag correctly.

When you thread wind the catch back in,  tip of the threaded section of the catch should be flush with the face of the button.