HK4: Heckler & Koch's Multi-Caliber Pocket Pistol
This guide details the process of converting the Heckler & Koch HK4 pistol between its available calibers (.22 LR, .25 ACP, .32 ACP, .380 ACP) using its interchangeable barrel and magazine system. It covers the simpler centerfire conversions and the more complex rimfire conversion requiring breech face manipulation. Expert Ian McCollum highlights the innovative design and manufacturing techniques.











