Ordnance QF 25 Pounder - Ammunition

Ammunition

The 25 pounder fired separate ammunition; the projectile and the propelling charge in its usually brass cartridge case with its integral primer were loaded separately. Being a QF gun the cartridge case provided obturation.

There were two types of cartridge. The 'Normal' contained three cloth charge bags (coloured red, white and blue). White and/or blue bags would be removed from the cartridge to give "Charge 1" or "Charge 2", leaving all three bags in the cartridge case gave "Charge 3". The cartridge case was closed at the top with a leatherboard cup. The second type of cartridge was "Super"; it provided charge "Super" only. The cup could not be removed from the cartridge case. In 1943, an Incremental Charge of 5.5 oz (160 g) of cordite (Super plus) was introduced to raise the muzzle velocity when firing AP shot with charge Super; this required that a muzzlebrake was fitted. Adoption of "upper register" (high angle) fire needed more charges to improve the range overlap. This led to the development of the "Intermediate Increment" of 4oz cordite, which was introduced in 1944. The bags were striped red and white to indicate that they should only be used with Charges 1 and 2. When one bag was used with Charge 1 it provided Charge 1 1/2. When one was added to Charge 2 it provided Charge 2 1/3, and two bags, Charge 2 2/3. This give a total of 7 charges instead of 4.

There were many marks of cartridge mostly differentiated by propellant type. Double base propellant (nitrocellulose/nitroglycerine) was the UK standard but one mark used US single base (nitrocellulose only). However, triple base nitrocellulose/nitroglycerine/picrite was used throughout the war and eventually replaced all others.

The 25 pounder's main ammunition was the High Explosive (HE) streamlined shell with a 5/10 CRH ogive and boat tail. It was also provided with base ejection smoke (white and coloured), star shells, and chemical shells. Incendiary and coloured flare shells were developed but not introduced into service, and smoke shells were sometimes reloaded with propaganda leaflets or metal foil "window". The UK did not develop a WP smoke shell for the 25 pounder.

For anti-tank use, the 25 pdr was also supplied with a limited amount of 20 pounds (9.1 kg) solid armour-piercing (AP) shot, later replaced with a more potent version with a ballistic cap (APBC). The AP shot was fired with maximum charge, Charge No. 3, Super, or Super with Super Increment depending on the ordnance mark, as muzzle velocity was critical in direct fire for penetration and a flat trajectory.

A shaped charge anti-tank shell was under development in Canada, but the introduction of the QF 17 Pounder, an anti-tank gun, in 1944 ended its development. After the Second World War, the UK replaced AP shot with a HESH shell. Coloured marked shells (dye and PETN) were also developed but not introduced.

The standard fuze is No 117 Direct Action (DA). No 119 (DA and graze) was also used. Combustion or mechanical time fuzes were used with base ejection shells and mechanical time with graze were used with HE. VT fuzes were used from the end of 1944 and subsequently replaced by CVT fuzes.