USMC5810

Leave the mag fully loaded for a while. Could just be a new issue. I have the same problem with a new mag. It is getting better after a few hundred rounds. Meanwhile short load it 1 round and see if it does better.

Are you useing the correct shell holder? If you have a 30 degree countersink, use a drill motor and run it in one or two for a second or so and see if that changes things. If you can get a picture of the pocket that would help.