Abstract: A hybrid firearm receiver includes a receiver body having a first end, a second end opposite the first end, a substantially planar bottom surface extending from the first end to the second end and transitioning to two upwardly extending opposing sidewalls, and a top end, the receiver body extending along a longitudinal axis from the first end to the second end. The first end is integrally formed with the receiver body and includes a circular first cavity and a smaller circular second cavity below the circular first cavity. The second end includes an aperture. The axis extends through a center of the circular first cavity and through the aperture and is below the top end. The circular first cavity may be configured to receive a portion of an AR-15 rifle stock assembly. The aperture may be configured to receive an AK pattern rifle barrel.