I'd do a muzzle flash in A/E or combustion. Are you using any of these to put your scenes together? In Maya you can get by with creating a light. Place it by the muzzle. Work on it's attributes. Animate it flashing on & off. Maybee even animate it's movement. You can also create a primative of your choice. Apply a shader. set color, transparency & incandescence. Animate it on & off. It is a flash. Not much time to study what happened. Remember it's all smoke & mirrers! Good Luck Bob