Propellant

PROPELLANT
British artillery propellants were originally called cordite, a double base propellant which was introduced into British service during 1891-3. Double-base propellants were a chemical mixture of nitrocellulose, nitroglycerine and additives. They were the main propellant used throughout WW2. There were various compositions that evolved and several types were available for each typeof gun, for example 5.5-inch initially had W and WM and RDQ (a triple base propellant), these had far less nitroglycerine than the original cordite. W was the 'standard' propellant for artillery at the beginning of WW2. By WW2 most field artillery ammunition, whether QF or BL, had propelling charges in bags.
Before WW2 most charge bags were made from worsted wool or shalloon (fine wool used toline suits). Nevertheless cambric (linen or cotton) was used with 25-pdr, although cotton and linen were notable for incomplete burning, but this did not greatly matter with metal cartridge cases fitted with caps to close their front ends. It was an issue with BL guns (glowing embers in the chamber could ignite a charge bag, although swabbing-out was used to deal with this) so silk or shalloonwere preferred. Silk had barrel wear reducing properties, which increased its attraction.
Having several types of propellant, eventually 7 for 5.5-inch and 10 for 7.2-inch, led to problems. As guns wore the change in muzzle velocity (MV) varied with the type of propellant. Furthermore different production 'lots' of the same type of propellant performed slightly differently (although weightswere adjusted for differences in propellant energy), which was exacerbated in worn guns. These problems required propellant to be sorted into types and lots on the gun position. The Gun Position Officer (GPO) could order the type and lot for use in a particular shoot, and this ensured consistency in the fall of shot. However, the accuracy of predicted fire was reduced if the guns were notcalibrated for the type and lot in use. In the last months of the war there were so many different types and lots on gun positions that sorting had to be abandoned, which had an adverse effect on the accuracy ofpredicted fire.
Later in the war some US single-base (nitrocellulose) propellant was taken into service. Before this the British had generally avoided single-base propellants due to itsdrawbacks, although NCT had been used in WW1 but was declared obsolete when the war ended. Most notably it was hydroscopic (it absorbed moisture). However, Dupont had created a 'non-hydroscopic' (NH) propellant that was adopted by the US. During the war the British, building on pre-war research, started introducing picrite based propellant, because it was flashless and cool burning. They calledthese double-base with picrite, although today they are usually called triple-base, but were produced in double-base production facilities. These were flashless and used carbamite instead of volatile solvents as a gelatiniser, and carbamite (diethyl diphenyl urea) was also a very good stabiliser. Picrite, a cover name for nitroguanidine, is a nitrogen rich explosive.
The 3 types are basicallyprepared as follows:
• Single-base - nitrocellulose dissolved in ether and alcohol
• Double-base - nitrocellulose dissolved in nitroglycerine
• Triple-base - nitrocellulose dissolved in nitroglycerine with nitroguanidine (picrite) added
The ballistic properties of artillery propellant are described in terms of its force, vivacity and form. Force is the energy content, vivacity is the intrinsic rateof burning and form is the shape of the propellant and affects its actual rate of burning and hence the rate at which its energy is released.
Propellant shape is a critical issue because, along with chamber pressure, it affects its burning speed. The British generally used stick shapes called 'cords' (hence 'cordite'), with the sticks being between 1/10th and 1/20th of inch in diameter and up...