Another Gunner Airsoft custom gun to satisfy those who are into collecting custom airsoft guns. This one allows you choose the markings on your metal receiver, the spring to whatever velocity you want it to shoot, and a big muzzle to boot... "Based on a Dboys M4, You can choose marking on the receiver. JG Shrot FF Rail, Big Rebar Cutter muzzle, Short ACE Stock, The red-dot scope shown in Picture not included."