A target version of the .22 caliber 58x series, the 540X, was used by the US military[3] as a training rifle and later disposed through the Civilian Marksmanship Program.

The bolt pictured is a pre-1975 locking model from a .308 Winchester caliber rifle.

It has a smaller ejection port than similar bolt-action rifles, and no bolt lug raceways.

Designed by former Office of Strategic Services (OSS) officer Mitchell WerBell III as a considerably more robust version of the silenced De Lisle carbine for special and clandestine operations in Indochina.

While WerBell's original design was a modified Destroyer carbine, most of the carbines delivered to the US Army by the Military Armament Corporation (MAC) were Model 788 rifles converted to fire 9×19mm Parabellum rounds, fitted with a silencer and a Tasco 4× magnification power scope, and modified to accept Walther P38 magazines due the shortage of surplus Spanish guns in the American market.