4MR Ranch goes over the Warhammer Armament MP5K variant, explaining that there are three key components needed to achieve the popular "super safety" rapid-fire functionality: the MP5 firearm, an AR-pattern fire control group lower (like the Lee Sporting LS5), and an M5 slip trip lever. They emphasize that due to the MP5's manufacturing process, some fitting and tuning is often required for reliability, and points out Warhammer Armaments' use of a rounded hammer to preserve the weapon's intended roller-delayed recoil impulse.