Learn more about the Heckler & Koch's first pistol that can fire 4 calibres, the HK4 in this The Firearm Blog video... "Heckler and Koch made a name for themselves when they began producing rifles, but in the mid 1960s they decided to expand their product line to include pistols. The result was a caliber convertible, small handgun that could fire .380, .32, .25, and .22 cartridges by having the end user do a quick conversion."