For making rapid bullets, you need to use Fast loop. If you have Tgf, you need a Fast loop extension. In MMF, there´s already Fast loop (Special conditions).

If you try to make rapid bullets like that (without Fast loop):

Lets take for example a duckshooting game with rapid bullets

Upon pressing "Shift"
-Create "bullet" at 0,0 from "gun"

Always
-Set X position of "bullet" to X position of "bullet"+50

Collision between "bullet" and "duck"
-destroy "bullet"
-destroy "duck"

There´s a problem. The bullet may jump past the duck, and the duck will not be destroyed.

But, if you make it WITH Fast loop:
Example is still the duckshooting game

Upon pressing "Shift"
-Create "bullet" at 0,0 from "gun"

Always
-Start loop "move bullet" for 50

On loop "move bullet"
+ "bullet" is not overlapping "duck"
-Set X position of "bullet" to X position of "bullet"+1

Collision between "bullet" and "duck"
-destroy "bullet"
-destroy "duck"

Like that, and it should work. And thats all because Fast loops. They are awesome.