Abstract: An automatic pistol of the breech block type which is interconvertible to fire sub-caliber cartridges. The frame, handle, slide, ejector and firing mechanism of the larger caliber pistol are used when converting for sub-caliber usage. A sub-caliber barrel is mounted in the slide and detachably connected to the frame by a pivotal link. An interchangeable barrel bushing adapted to support the forward end of the sub-caliber barrel is inserted in the slide. At the forward end of the slide a recoil spring is tensioned to operate the slide upon firing of a sub-caliber cartridge. A sub-caliber magazine is inserted in the handle. The extractor is cambered and is sufficiently flexible to capture and extract cartridges of both calibers. The cartridge locating recess in the breech face is that of the larger caliber.

Abstract: The accuracy of a semi-automatic piston of the locked breech type is improved by tapering each side of the tenon at the rear of the barrel and correspondingly tapering the tenon engaging recess in the slide, thereby assuring that the rear of the barrel is accurately centered at the breech face of the slide and is prevented from moving laterally. The mating surface of the under-barrel lug is contoured such that when the barrel is in battery the slide stop pin bears against the under-barrel lug in such a manner as to cause the barrel to be jam fitted between the slide stop pin and the underside, top surface of the slide thereby preventing any vertical movement.