Since the close of World War 2, when infantryman relied on thrown hand grenades or rifle grenades fired from the muzzles of their service guns, the US military was attempting to develop a multiple-shot grenade launcher. One such project (under a US Marine Corps directive) fell to the Naval Ordnance Station (NOS) of Louisville, Kentucky who headed the "NOS EX 41" initiative, a compact grenade projecting system firing a combined low/high pressure 40mm grenade through a conventional pump-action facility. By this time, the USMC had already adopted the M203 underbarrel single-shot grenade launcher to replace their Vietnam War-era M79 single-shot series and used the vehicle/tripod-mounted Mk 19 automatic launcher in number. Picatinny Arsenal was charged with development of a new 40mm grenade to bring together the qualities of the M203's 40x46mm grenade with the qualities of the Mk 19's 40x53mm type.
The EX 41 became a compact weapon taking the general form of an automatic weapon with the action of a shotgun. The design was of an in-line approach (all major components set behind the other) with a sizeable buttstock, smooth barrel assembly, underslung pistol grip with trigger unit and an optics mounting. A magazine tube was installed under the barrel and operated through the pump-action facility in much the same way a traditional pump-action shotgun was operated. Overall weight was 10 kilograms with a running length of 914mm with a 279mm long barrel assembly. Each 40mm grenade exited the barrel at approximately 152 meters per second out to a maximum range of 1,500 meters. The tube magazine held four ready-to-fire 40mm grenades expanding the role of the warfighter considerably. Each grenade was of a "hybrid" design incorporating qualities of both low and high pressure grenade projectile munitions to contend with inherent recoil forces while providing a useful exiting velocity and, therefore, longer effective engagement ranges.
In the end, only a single prototype form was ever completed by NOS and this development weighed in heavier than the anticipated 7 kilograms. The expected 3,000 meter range was also limited to the aforementioned 1,500 meter reach. The M203 and Mk 19 series remained the standard US military grenade launchers for the interim and the EX 41 prototype was passed on to privately-held firm of Knight's Armament Company of Titusville, Florida for further work to which its condition since then remains largely unknown. Regardless, the type was never adopted by the USMC nor any other American service branch and has more or less fallen to the pages of history. Its last notable recorded presence was during November of 1995.
The EX 41 was also known under the name of "Shoulder-Fired Weapon" (SFW).