Discarding sabot projectile.

Anti-tank (AT) guns initially used solid steel armour piercing (AP) rounds which derived their penetrating power from kinetic energy. As armour increased in thickness it became necessary to achieve higher muzzle velocities in order for a projectile to penetrate, but steel shot tended to shatter on impact at velocities upward of about 823 metres (2700 feet) per second. A variety of projectile types were developed to maximize muzzle velocity and penetrating power. A soft metal cap was added first to try to prevent the solid shot from shattering. It was found that these APC, or armour piercing, capped, rounds were unstable in flight, however, and so a ballistic cap was introduced in APCBC (armour piercing, capped, ballistic capped) rounds to improve range and accuracy. The best solution to the problem was found in armour piercing, discarding sabot (APDS) rounds, introduced in August 1944. Development had been influenced by Canadian General A.G.L. McNaughton, a gunner of the Great War who had commanded the Canadian Army in Britain until November 1943. APDS rounds featured a tungsten-carbide core projectile within a steel jacket that was shed upon leaving the muzzle. Tungsten-carbide was expensive to produce, and so heavy that a full-bore projectile could only be fired at relatively low muzzle velocities. By using the discarding jacket, however, the full force of the exploding propellant was applied to a ballistically-superior and very dense core, resulting in much higher muzzle velocities and improved penetrating power.

Eventually, the upper threshold of development of kinetic energy anti-tank weapons was reached, after which guns became too large to be practicable. Instead of kinetic energy resulting from high velocity, shaped- or hollow-charge projectiles relied on explosive chemical energy. When such a projectile struck, "a fuse detonated explosive at the end remote from the shaped cavity at the front of the round and . . . created a jet of molten metal that would penetrate armour plate and spray a mass of flame and melted metal fragments into the interior of a tank. Hollow charge projectiles were ideal for low-velocity, hand-held anti-tank weapons" such as the British PIAT (Projector, Infantry, Anti-Tank), the American bazooka, and the German Panzerfaust and Panzerschreck (Donald E. Graves, South Albertas: A Canadian Regiment at War, 1998, p. 365).