From what I have heard, he does not use "Lead" bullets, but either wax or paper. Soooo basically he does not have to aim, because the pieces act like a shot shell.
Furthermore, the use of blanks creates the illusion of accuracy while fast drawing, when in fact just aiming a gun loaded with a blank cartridge in the general direction of a balloon (one of Munden's choice targets) at close range will destroy the target where a live round would likely miss. Firing blanks also means a very low recoil which in turn provides for a rapid succession of rounds to be fired, yet in real life applications would be pointless.