Lock the bolt back, and look up the front inside of the mag well wall to confirm that the upper receiver ledge is not protruding over the mag well wall to block the mag from going all the way up.


If you are good so far, then pull a mag apart, and using just the body of the mag only, see if you can get it lock in the mag well with both the bolt held back, and the bolt forward.

If you have problems still, them make sure that the bottom of the mag well is not binding on a ledge on the side of the mag body.  Also, pull the mag catch assembly, lock the bolt home, shove the mag all the way up so its top of feed lips are tight against the bottom of the carrier , and take a look in the slide slot of the receiver at the mag catch slot.

What you want to see, is the slot in the side of the mag bottom edge, just a touch higher than the bottom of mag catch slot in the lower receiver.

Lastly, when you pull the charging handle all the way back, the front face of the bolt should be proud of the back edge of the ejection port window about 1/8" to 1/4".