If hes using an A1 stock, make sure the upper stock screw (the one with the hole in it) is an A1 screw.
If you use the A2 screw, you will get all sorts of intermittent feeding issues that will drive you nuts.
"If the rule you followed brought you to this,
of what use was the rule?"
“The enemy is anybody who's going to get you killed, no matter which side he is on.” - Joseph Heller