While Heckler & Koch today has a number of well-known firearms in world-wide use, some of their early products are nearly forgotten. Speaking of which, let's talk about the HK4.
Rising from the ashes of the old Mauser company after World War II, two former Mauser engineers, Theodor Koch and Edmund Heckler, later joined with a third, Alexander Seidel in 1949 to form Heckler & Koch in an old fire station in Oberndorf.
With West Germany rebuilding, the new machine works busied itself with making household items like tools and bicycles until the mid-1950s when they began reworking the roller-delayed blowback Spanish CETME rifle-- which was designed by German engineers-- as the gun that became the HK G3. Following up with the HK54, which became the now-famous HK MP5, by the 1960s Heckler & Koch were looking to get into the handgun market.
That's where Seidel came in with an ace in the hole. Born in 1909, he was the holder of dozens of firearms patents and had been the primary designer of what was arguably Mauser's most successful semi-auto pistol, the HSc.
Using the HSc as a base, in 1963 Seidel began working closely with fellow HK engineer Tilo Moller on a pistol that would have a breech bolt with a firing pin operable at different angles. The cool thing about this is that it would allow the gun to accept barrels of a different caliber, in both rimfire and centerfire variety.
HK's pistol had another selling point, the fact that the same grip module (Griffstück) and slide (Verschlußstück) could accommodate four different calibers: .22 LR, .25 ACP, .32 ACP, and .380 ACP. All that was needed was a swap of the magazine and barrel.
This allowed Germans, subject to strict firearms laws, to get the most bang for the Deutschmark out of a single pistol while also giving HK the ability to pitch the gun to European law enforcement who could shoot cheaper rimfire ammo to train with while carrying a more full-power duty round (e.g. .32/.380, which were long popular in German police use).
In all, about 40,000 HK4s were produced before the line closed and Heckler & Koch moved on to other pistol designs. In Germany, they were used by Zoll customs police and by the West Berlin police force.
Notably, the company has stayed away from handguns chambered smaller than 9mm since then, another factor that makes the HK4 an interesting footnote for HK collectors. For more on these fascinating guns, check out the Unblinking Eye and HKP7 who have done a lot of homework on these.
If you like rare and interesting firearms, or just want to be the only guy on the range with something like the HK4, check out our carefully curated Collector's Corner and Military Classics sections.