OVERVIEW: The 20-pounder Armor-Piercing (AP) round is a solid shot kinetic energy projectile developed for the British 84mm (20-pounder) tank gun. It was designed to defeat enemy armored vehicles through direct-impact penetration using high-velocity, full-caliber shot.

DETAILS: The 20-pounder AP round was used primarily with the Royal Ordnance QF 20-pounder gun, which equipped post-WWII British tanks such as the Centurion Mk 3 and Mk 5 before the adoption of the 105mm L7. The AP round was a solid, non-explosive projectile relying purely on kinetic energy to penetrate armor. Early versions used uncapped AP shot, while later developments included APCBC (Armor-Piercing Capped Ballistic Cap) designs to improve ballistic performance and armor penetration. Typical muzzle velocity ranged between 1,020 to 1,050 m/s, with penetration performance of roughly 200 mm of rolled homogeneous armor at short range. It was used alongside APDS (Armor-Piercing Discarding Sabot) rounds, but the full-caliber AP shot remained a simpler and more rugged option.

ROLE SUMMARY:
Category: Tank Gun Ammunition
Primary Use: Anti-armor
Function: Direct-impact kinetic penetration
Strong Against: Rolled homogeneous armor, lightly sloped plate
Weak Against: Composite armor, ERA, angled heavy armor
Platform: Centurion Mk 3, Mk 5, and related vehicles with 84mm QF 20-pounder gun
Integration: Standard AP ammunition for 84mm 20-pounder; later replaced by 105mm L7 systems

SOURCE:
Janes Ammunition Handbook ; British Army Armament Training Publications ; Tank Museum (Bovington) Archives ; https://en.wikipedia.org/wiki/Ordnance_QF_20-pounder