Why does my magazine sometimes fall out?

If the magazine is fully loaded (to capacity) and you are inserting it on a closed bolt, the magazine does not have the opportunity to seat properly. Always insert a fully loaded magazine on an open bolt, regardless of caliber.

If it is an empty magazine, or you are inserting (loaded or empty magazines) on an open bolt, check to make sure the magazine release lever is installed correctly. More often than not, it is simply a matter of the lever and button needing one more turn/rotation to get it into proper position.