This thing is fully built internally and shoots like a beast. Shoots 550 fps with .20g bbs which is insane for a semi auto rifle. The base gun was a G&P zombie killer M16 which is discontinued and it's in pretty good condition. Semi auto locked internally. Only "issues" would be the safety doesn't work, no dummy bolt, and it over hops almost any bb weight but all that would need is a different nub or the one in it shaved down. Literally over hops .43g bbs, but it shoots insanely far and accurate. The gear box runs smooth and it has absolutely perfect air seal.  This thing is just crazy, I've never fired anything else like it. Comes with one good working 300 round high capacity magazine. No battery but I recommend 11.1 Open to offers Build list: Shs 18:1 gear set shimmed and greased AOE corrected Evike monster torque motor Aluminum double o ring cylinder head Aluminum concave piston head Full metal rack piston Aluminum o ring nozzle 500 mm 6.02 tight bore barrel Metal hop up chamber R hopped barrel, modify flat hop bucking and nub Maxx cylinder M130 spring Wired to deans