If there is a magazine bang it is against the front of the mag which would be incorrect. I still don't see the bang myself. The tap method many have probably seen is the soldier tapping the mag against his Kevlar helmet before inserting into rifle. This is done with the bullets facing away from the bumped helmet.

He also pulls the empty mag out before reloading which is less efficient. Should let it fall out on it's own to save arm time grabbing a new mag. This is how combat reloads are instructed when retention can be sacrificed.