Since the mid-1960s the Heckler & Koch MP5 has become the most widely used submachine gun in the world, especially among counterterrorist and special-operations units. Lightweight and offering a blistering rate of fire of 900 rounds per minute in some versions, the MP5 quickly earned a reputation for accuracy due to its fixed yet free-floating hammer-forged barrel and close-bolt operating system. Its sights, which consist of a front hooded post...