The main armament of the Sherman Firefly was the Ordnance Quick-Firing 17-pounder. Designed as the successor to the British QF 6-pounder, the 17-pounder was the most powerful British tank gun of the war, and one of the most powerful of any nationality, being able to penetrate more armour than the 8.8 cm KwK 36 fitted to the German Tiger I or the Panther tank's 7.5 cm KwK 42. The Firefly 17-pounder was able to penetrate some 163 mm of armour at and 150 mm at using standard armour piercing, capped, ballistic capped (APCBC) ammunition. Armour piercing, discarding sabot (APDS) ammunition could penetrate some 256 mm of armour at 500 m and 233 mm at 1,000 m, which on paper could defeat the armour of almost every German armoured fighting vehicle at any likely range. However, war production APDS rounds lacked accuracy, and the 50 mm penetrator was less destructive after it had penetrated enemy tank armour than the 76.2 mm APCBC shell. APDS ammunition was rare until the post-war period. While the Sherman Firefly was capable of carrying 77 rounds of ammunition, design features of the tank meant only 23 rounds were easily and readily available when the tank was in action.