Fixing a UTG shotgun

i know how much airsoft guy hates this gun but i had two UTG shotguns and they broke.both. so i took them both apart down to the last screw. then i rebuilt one so-called workin shotgun. all of a sudden there are problems. first whenever i cocked the gun the entire mag would empty into the gun. then i fixed that and now the gun automaticlly slam fires. if anyone knows how to fix it that would be great.