As stated in the title, we have a bit of Frankenrifle's monster here. The lower receiver group consists of a POF, single stage trigger pack, a Magpul STR stock and POF fouble QD end plate. The upper receiver group is nearly a complete Aero M4e1 except for the Rainier Arms muzzle break (to tame the clavicle disintegrating power of the AR's recoil impulse).