The 7.5 cm PaK 40 (7.5 cm Panzerabwehrkanone 40) was a German 7.5 centimetre anti-tank gun developed in 1939-1941 by Rheinmetall and used during the Second World War. PaK 40 formed the backbone of german anti-tank guns for the latter part of World War II, and was used in most war theatres. It fired a 75mm AP shell out to an effective range of about a mile in a direct-fire role, with enough energy to defeat pretty much any Allied tank except the late-war Russian heavies. It was fairly light weight given its effectiveness, and makes one hell of a concussion when fired.
While they (Forgotten Weapons) normally stick to small arms here, this beast of a gun was just way too impressive for him to not pay attention to. He was at a cannon and machine gun shoot just recently where some folks brought out what is (I believe) the only functional Pak-40 in the United States. And shot it.