If you cant afford the plug in you can draw muzzle flashes in photoshop and overlay them in AE using overlay or color dodge. Since they are only on for a few frames (make sure you dont use the same image for more than one frame) they dont have to look amazing..just good. As far as gun blow back, most of the Airsoft guns are way too slow. The chamer takes like a whole second to move back and forth. Just make sure the actor fakes it.
As far as wound to the headh, you may be able to get away with using particular for the blood, if you make it look cloudy(like spray bottle) and quick. Track a black/red dot to the head, and obviously dont have a close up of it or anything.
As you can tell I’ve done this before with pretty good results. I remember the producer screaming, “We dont have liability insurance for this!!” Excellent. Okay I made that last part up, but that would be cool.
Spock.