my ics m4 came with a spilt gear box. maby it is put metal, i figured it looked aluminum, onlny way to tell is to take a sample to a machine shop and get an expert opinion, good idea for a project though. that looks like a pritty wicked kit, even though it doesnt come with a piston cylender, anyway i gotta crash, i have to be up in 4 hours, Booooo