Most of its development was at Naval Ordnance Station Louisville for the US Marine Corps in order to replace the single-shot M203.

In its final form, the EX 41 was intended to weigh as little as 6.8 kg and have a range of up to 1500 m. The program never progressed beyond a single prototype and in November 1995, the design was sent to Knight's Armament Company for further development.

High-velocity ammunition such as the M430 HEDP and M918 practice grenades were fitted to the low-velocity cartridge cases, in order to have a longer effective range with a lower recoil.

An optical sight of unknown manufacture was added to the top of the receiver to take advantage of the extended range of the ammunition.

After discussing the engineering difficulties and use of non-standard 40mm rounds, Knight and Olsen agreed that the program was, "Pretty dangerous."