The H&K MC51 was a weapon set to appear in the original version of Resident Evil 2 (RE 1.5) which was subsequently never released. It was replaced by the MAC-11 in the final version of the game. Some, however, have managed to re-add the weapon to the game in their own builds of 1.5, using the files (such as the inventory icon) extracted from the early betas of RE2.