Abstract: The frame of a hand pistol has in its forward end a pair of spaced furcations between which the lug on a removable gun barrel is pivotally mounted by means of an adjustable mounting pin, which permits the barrel to be pivoted between an open or loading position, and a closed or firing position. The adjustable pin comprises an Allen-head screw having a cylindrical head positioned snugly in a circular bore formed in one furcation, and a reduced-diameter, externally-threaded shank, which extends coaxially through a bore in the barrel lug, and which is threaded into an annular nut that is positioned snugly in a registering bore in the other furcation.