Glossary of British ordnance terms

Breech loading, in its formal British ordnance sense, served to identify the gun as the type of rifled breechloading gun for which the powder charge was loaded in a silk or cloth bag and the breech mechanism was responsible for "obturation" i.e. sealing the chamber to prevent escape of the propellant gases.

A single-use "vent sealing tube", a type of primer not dissimilar in appearance to a blank rifle round, was inserted into the breech for firing the gun.

A special cartridge was developed for BL 9.2-inch (234 mm) guns on HA mountings, with provision for a wooden (beech) stick to be inserted through the centre to prevent the shell slipping back on elevation.

[2] Although fixed ammunition allows for a rapid rate of fire in small to medium guns, BL is a better choice for heavy calibre guns; propellant was loaded in a number of small fabric bags, because a single bag holding the full charge would be far too big and bulky for the handlers to lift.

[4] "Cartridge" in British ammunition terminology typically refers to the physical object containing the propellant that a gunner loads.

For small arms and fixed QF artillery ammunition, e.g., the .303 or 18-pounder respectively, this denoted the complete round, that is, the cartridge case, percussion cap or primer, propellant charge and projectile.

British cartridges contained gunpowder until about 1892, and thereafter sticks of cordite bound together with an igniter pad, if necessary, in a cloth bag, usually silk.

The "stick" nature of cordite gave the cartridges a degree of rigidity and hence they retained a tubular shape and could be handled and loaded as a solid unit even without a case.

They were of cast or forged (three- and six-pounder) steel and contained a gunpowder bursting charge slightly smaller than that of a common shell, a tradeoff for the longer heavier nose.

By World War II they were superseded in Royal Navy service by common pointed capped (CPC) and semi-armour piercing (SAP), filled with TNT.

The abbreviation cwt stands for hundredweight, which, despite the name, is equal to 112 pounds (51 kg), and signifies the weight of the gun barrel and breech.

This data would be provided to the transmitting station (TS), where a firing solution would be calculated and passed on to the gun turrets as the correct degree of training and elevation.

This wear can reduce muzzle velocity and hence range, affect accuracy, produce unstable projectile flight, and, eventually, cause the gun barrel to fail.

Britain first used pure TNT for land warfare shells from late 1914, but this proved expensive and difficult to manufacture in the necessary large quantities, and was also inefficient as much energy was output as heavy black smoke.

E.g. if the preponderance was quoted as 4 tons 2+1⁄2 cwt (4.2 t) as for the RML 17.72-inch "100-ton" gun, the breech end sat with that weight on its mounting, enough to ensure stability but not enough to hinder changes in elevation.

The term was dropped when it became meaningless with the replacement of trunnions by more modern methods of mounting guns on recoil slides in the 20th century.

Fixed QF was suited for rapid loading, especially at high angles, and was limited by the total weight of cartridge and projectile, which had to be easily handled by one man.

This system was suitable for howitzers as it allowed the gunner to remove part of the cordite charge before loading, if required for shorter ranges.

This allowed a sliding block, which can generally be operated faster than a BL screw mechanism, and is characteristic of small to medium artillery.

[23] QF also, by rigidly fixing the position of the primer, igniter and cordite charge in the case relative to each other, improved the chances of successful firing compared to BL with its flexible bags.

For guns larger than 6 inches (150 mm), it becomes impractical as the cartridge case becomes unwieldy for manual operation, and it does not allow charges to be loaded via multiple bags as BL does.

Typical examples were in the QF 13-pounder, 18-pounder, and BL 60-pounder Mk I guns, all dating from 1904 to 1905, where the oil, pistons and springs were integrated in a tubular housing above the barrel.

This configuration made the entire recoil system vulnerable to enemy gunfire, and it was protected to some extent in the field by being wound with thick rope.

When World War I began, both the army and navy were in the process of introducing a "hydro-pneumatic" recoil system in which the recuperators were driven by air compression rather than springs.

They had a heavy solid nose and a medium amount of TNT explosive, giving them the capability to penetrate steel superstructures and a small thickness of armour.

The projectile was made up of layers of iron rings within a thin cast-iron shell wall, held together with lead between them, with a hollow space in the centre for the bursting charge of gunpowder.

This was the traditional, reliable British method of fully igniting powder charges in BL guns to fire projectiles, especially large shells.

[24] "Windage" as applied to British muzzle-loading ordnance referred to the difference between a gun's bore and the projectile's diameter, typically 0.1–0.2 inches (2.5–5.1 mm).

From 1878, after several years of unsuccessful trials, a fairly effective system of concave copper discs called gas-checks was introduced between the charge and projectile; they expanded on firing and sealed the bore.

It provided greater radial strength, i.e., it better withstood the gas pressure attempting to expand the gun's diameter, than previous "hoop" construction methods of similar weight.