This is a KJW M4 designed by Tanio Koba the inventor of the Marui gas system A little beat up but I just went through and rebuilt the whole gun with real steel detents. Gun shoots super crisp and is one of the lightest GBBRs to run around with Real steel PXT keymod rail system Cradle TDC hop up Falcon Tightbore 1 Cradle V1+ bolt shoots 440 (adjustable) 1 KJW V1 bolt shoots 500 with cradle adjustable floating valve. 1 KJW V1 bolt carrier 7 mags 3 good 4 with easy to fix leaks I just ran out of O-rings