Held, air gun (i.e., a gun that expels a projectile using compressed air, carbon dioxide, propane, or similar gas) replicas of AR/M-16 variant firearms that provide housing for a hammer and firing mechanism with substantially the same design as AR/M-16 variant firearm receivers, and mounting points for attaching an upper assembly containing a barrel and bolt, are "firearm frames or receivers," and are, therefore, "firearms," as that term is defined by 18 U.S.C. 921(a)(3)(B), and its implementing regulation, 27 CFR 478.11.