Ordnance QF 20-pounder

The Ordnance QF 20 pounder (known as 20 pounder, 20 pdr or simply 20-pr) was a  British 84 mm (3.307 inch) tank gun.

It was introduced in 1948 and used in the Centurion main battle tank, Charioteer medium tank, and Caernarvon Mark II heavy tank.

It was the improved successor to the effective Ordnance QF 17 pounder and the predecessor of the 105 mm L7 gun.

Design and development
The gun was developed by the Royal Ordnance Factories.

As fitted to the Charioteer, it ran through two models:
 * Model A without a fume extractor.
 * Model B with a fume extractor.

The L7 105 mm tank gun was developed from the 20 pounder. In 1954, the original version of the 105 mm was made by re-boring the tube of a 20 pounder barrel.

Service history
The gun was fitted predominantly to the Centurion tank, seeing action with British and Australian forces.

One gun was fitted to a Swiss pre-production Panzer 58.

Performance
The 20 pounder's APCBC projectile had an initial muzzle velocity of 1,020 metres per second and could penetrate 210mm of rolled homogeneous armour (RHA). However, these conventional rounds were rarely used.

The APDS projectile had a muzzle velocity of 1,465 m/s and could penetrate 30 cm of RHA.

The 20-pounder could also fire high-explosive and canister shot shells.