Blowback-operated semi-automatic pistol based on Mauser HSc design. Chambered for .22 LR, .25 ACP, .32 ACP and .380. These calibers easily converted by switching barrels, recoil springs and magazines. Rimfire model could be changed by rotating breechface. Conversion kits available for all calibers. Barrel 3" long; finish blued, with molded plastic thumb rest grips. Pistol sold from 1968-1973 as Harrington & Richardson HK4 and so marked. Discontinued in 1984.