Apparatuses, systems, and methods are disclosed for use in or with firearms. A firearm receiver includes an elongated channel machined or 3D printed from a metallic material, and has a front end and a rear end. The firearm also includes a front trunnion having a rear portion coupled to the front end of the elongated channel and having a front portion configured to couple to a handguard. Also includes is a rear trunnion coupled to the rear end and configured to receive an accessory adapter.