I will be covering this more in tutorials but first I wanted you guys to see what a bump fire is:
This is not an Full-automatic Weapon, it is merely a Semi-automatic weapon that is being fired using a sort of trick shot skill.
Bump firing is using the recoil of the gun and your secondary arm to act as spring mechanisms to move the gun and trigger back and forth on your trigger finger. This creates a very fast firing technique which is quite enjoyable and can be done with any Semi-automatic weapon. More on this later!