4.2 cm Pak 41
The 4.2 cm Pak 41 (Panzerjägerkanone —"anti-tank gun") was a light anti-tank gun issued to German airborne units in World War II. This gun was externally similar to the 3.7 cm Pak 36, using a modified version of the latter's carriage, but used the squeeze bore principle. While it was nominally a 4.2 cm (1.7 in) gun, the actual caliber was 4.06 cm (1.60 in) at the breech and tapering down to 2.94 cm (1.16 in) at the muzzle.