i need molding help


you see, i need a tutorial of how to make a mold, like show the steps. i was planing on making a clay assault rifle or battle rifle or ect. and the clay weapon was to be used to make my mold. i have seen adams ODST helmet mold making video but im still a retard here thinking how i can do that. Because i know i apply silicon on first like four layers, then what? and what part would be the mold to put the liquid plastic inside. because how can you get the mold part without braking it in two. i realy need help with this so please post a tutorial or post a link.

REMEMBER! i said weapons not helmets. helmets or armor pieces wont help because im dealing with guns here.