In the late 1970s, H&K decided that it wanted to offer a tactical shotgun for the police and security market. Having no experience with shotgun manufacture, they turned to Franchi in Italy – for whom they already handled sales outside Italy. Franchi produced a gas-operated semiautomatic shotgun for HK, who brought in the parts and did the final assembly themselves, in order to legally identify the guns as H&K products. About 1500 were built, and most of these were sold to security agencies in Germany, Austria, Spain, and Portugal. A small remained of unsold ones were imported into the United States in the late 80 and early 90s, apparently between 250 and 350.
The most interesting element of the H&K 512 to me it the inclusion of an A&W Diverter as an OEM part. The Diverter changes the shot pattern from a circle to a roughly rectangular shape between 3:1 and 4:1 height to width. On the 512, the Diverter was mounted vertically, to create a tall and narrow pattern – that is, a pattern ideal for hitting a target without pellets straying onto potential hostages right next to the target.