Hey, that's nothing, the one weapon that is jokingly referred to have a Pk of 2.0 (100% guaranteed to kill the target ... and the user) is the "Davy Crockett" nuclear recoiless gun.
The M28 120mm version only shoots the M-388 shell with a W54 nuclear warhead (0.01 to 0.25KT yield) 6,600ft (~1.98km)! At the shortest fuze setting, (1,000 ft), the shooter would probably get a radiation dose close to what is needed to kill 50% of those exposed!
Cold War equivalent of the Soviet 45mm anti-tank guns nicknamed "Proschai Rodina" (Прощаи Родина!; Adieu Motherland). Supposedly, the gunners have to wait until the enemy tank gets so close to penetrate the armor that they expect to be killed after firing a single shot!