8 Cm PAW 600 - Design and Development

Design and Development

In 1943 a specification was issued for a lightweight anti-tank gun that used less propellant than a rocket or recoilless weapon yet was sufficiently accurate to hit a 1-meter square target at 750 meters range. Rheinmetall-Borsig proposed a design to meet this requirement using the new high-low pressure ballistic principle, also known as the Hoch-Niederdruck system. In this system high pressure caused by the combustion of the propellant was confined to the breech section, which was relatively heavy, and did not act directly on the projectile. It was allowed to bleed gradually into the barrel at a controlled rate and lower pressure to propel the projectile. Thus the barrel could be exceptionally light in a weapon that still had the advantages which accrue from high pressure. The carriage too could be very light although initial prototypes carriages proved to be too light and had to be redesigned. The resulting PAW 600 (later redesignated 8H63) gun weighed about 600 kg, less than half that of the 7,5cm Pak 40 while having comparable armor penetration out to its full effective anti-tank range of 750 meters.

Unlike previous anti-tank guns which relied on firing steel projectiles at high velocities to penetrate heavy armor, the 8H63 was designed to fire shaped charge ammunition (called also hollow-charge ammunition, high explosive anti-tank, or HEAT). Because shaped charge warheads perform best when no spin is imparted on the projectile the 8H63 was a smoothbore design. To simplify development and manufacture the projectiles used were based on the widely used 8 cm Granatwerfer 34 mortar (actual caliber 81.4 mm). This allowed the use of existing tooling in the manufacture of ammunition, which reduced cost. The cartridge case was developed from the 10.5 cm leFH 18 howitzer.

The standard shaped charge projectile designated 8 cm W Gr Patr H1 4462 weighed 2.70 kg. The propelling charge was 360 gm of Digl B1 P (compared to a 3.8 kg propelling charge in a PAK 40) and with a muzzle velocity of 520 mps this had an effective range of 750 meters against a tank-sized target. Armor penetration was 140mm of vertical armor which was comparable to the 7.5 cm PAK 40 firing the rare and expensive tungsten-cored AP40 shot.