The thing on the right side of the mag well is the magazine safety. A tab on the safety engages a stud on the side of the magazine. With the magazine locked in place, the stud lifts the safety tab slightly and allows the trigger to be pulled. But the tab should not prevent the magazine from being inserted unless the safety lever is badly bent.
Last edited by DnPRK; June 24, 2013 at 10:43 PM.