Some very nice tutorial how to make a muzzle flash for your action movie. Many movies need some gun actions scene. Finally you don’t need After Effect for that composition you can composite it in mostly in any better Editing software like Final cut studio or similar.
And never use real guns on a filmset even not when you don’t have a alternative. A Filmmaker Friends of mine had the experience that the guy who bring the guns on the set was from the police and he bring just real guns some of them even don’t been unloaded.