In United States v. McCauley, 601 F.2d 336 (8th Cir. 1979), the defendant was convicted of possessing an unregistered firearm, namely, a machine gun.
The machine gun he had possessed was lacking a magazine necessary for automatic firing, however. The pertinent statutory definition of "machine-gun" was "any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger." Id. at 338.
The evidence demonstrated that the proper magazine for the type of weapon the defendant possessed was difficult, but not impossible, to obtain.
The court held that without evidence the magazine or an effective substitute was "completely unavailable," the weapon met the statutory definition of "machine-gun." Id. at 341.