Assuming you're gonna be using some kind of competent editing software you don't even need a realistic gun
doing film class and because we don't have loving guns here, I used a cardboard cutout with a gun printed on the side then just edited in muzzle flash onto a single frame, upped the frames saturation to simulate the light and threw in a gun sound
for a student film it works, you don't need to waste blank rounds for a class film because A: its unnecessary and might not give the desired effect and B: there are obvious risks. if anything you'd get more on your grade for showing editing skills