Reference / Paper · 1983
ATF's 1983 ruling that the YAC STEN MK II semi-automatic carbine, an open-bolt design with a fixed firing pin, is a machinegun under the NFA because it is readily restorable to automatic fire. The STEN dive's legal volume rests on it, and the Sterling Mk 7 dive applies it to open-bolt semi-automatic copies.
27 C.F.R. 179.11: MEANING OF TERMS The YAC STEN MK II carbine is a machinegun as defined in the National Firearms Act. ATF Rul. 83-5 [Status of ruling: Active] The Bureau of Alcohol, Tobacco and Firearms has examined a firearm identified as the YAC STEN MK II carbine. The YAC STEN MK II carbine is a 9 millimeter caliber firearm which has identical design characteristics to the original selective fire STEN submachinegun designed by Reginald Vernon Shepherd and Harold John Turpin. The weapon is blowback operated and fires from the open bolt position with the bolt incorporating a fixed firing pin. In addition, a component part of the weapon is a trip lever (disconnector) which has been modified to prevent more than one shot being fired with a single function of the trigger. The trip lever (disconnector) is designed in such a way that a simple modification to it, such as bending, breaking or cutting allows the weapon to operate automatically. Thus, this simple modification to the trip lever (disconnector), together with STEN submachinegun design features and components in the YAC STEN MK II carbine, permits the firearm to shoot automatically, more than one shot, without manual reloading by a single function of the trigger. The above combination of machinegun design features as employed in the YAC STEN MK II carbine are not normally found in the typical sporting firearm. The National Firearms Act, 26 U.S.C. 5845(b), defines a machinegun to include 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. The “shoots automatically” definition covers weapons that will function automatically. The “readily restorable” definition defines weapons which previously could shoot automatically but will not in their present condition. The “designed” definition includes weapons which have not previously functioned as machineguns but possess specific machinegun design features which facilitate automatic fire by simple alteration or elimination of existing component parts. Held: The YAC STEN MK II carbine is designed to shoot automatically more than one shot, without manual reloading, by a single function of the trigger. Consequently, the STEN MK II semiautomatic carbine is a machinegun as defined in Section 5845(b) of the Act.