The innovative team over at Wolverine took their original BOLT HPA system and redesigned it for a standard M4 V2 airsoft rifle. This simplified version requires no programming and is ready for use after attaching the wire and battery power source. The universal design of this HPA system allows it to be installed in all M4 style airsoft rifles that feature a Version 2 gearbox, and is not recommended for rifles with an extremely high rate of fire. A standard Wolverine battery or Valken 250mAh battery pairs nicely with this engine, but is not included with purchase. The true “Closed Bolt” system effectively traps the air within the rifle to line up your next shot before you even pull the trigger. Maximize your rifles full potential with the new REAPER M4 V2 Electro-Mechanical HPA Engine from Wolverine.