The valving system and finned "paintball" were designed and adapted for the M303 by my good friend Tom Kaye of Airgun Designs paintball fame (
www.automags.org ,I'm a moderator there).
AGD has a steel fire door at the end of a 100' hallway, that has many fist sized dents in it from the 303 projos. With speeds of up to 400fps, the
projos will knock the crap out of you.