When you fire your Buster when stationary, then begin moving soon after, this cancels the firing animation (and the internal timer that stops you from firing another shot), but the Buster still fires. You can make use of this by repeatedly tapping Up while standing still and firing at an enemy. Depending on how fast you manage to tap, you can, in effect, emulate a +2 or +3 Rapid stat on your Buster even if you're not equipped for that.