Skip to content

12.5 inch RML Technical Details

Some notes on the technical features of the 12.5 in 38 ton Rifled Muzzle Loaded gun from 1885, covering the mechanism in the gun carriage and fitted to the platform. The method of building the gun from wrought iron rod and constructing it using concentric coils to pre-stress the inner parts are illustrated in concept – there is no guarantee that the actual machinery used at the time bear any resemblance to that shown in the movie – concepts only. Gun design is covered briefly, concentrating on showing how internal pressure was measured using crusher gauges fitted to test guns. Finally, a method of measuring muzzle velocity is shown, and a hint given for the mathematics needed to calculate velocities at different ranges, which in turn resulted in range tables used for actual firings.

When watching this animation, bear in mind the technology available at the time. No computers , no electronics, rudimentary electrics (wet cell batteries). So measuring time (for muzzle velocity) used the known constant – gravity. Electric motors would be subject to speed variations depending on the state of the batteries. However, the level of mechanical skills were impressive. Machinery capable of finishing to an accuracy of a few thousandths of an inch on rotating masses weighing several tons were available, as were the artisans. Even more impressive was the level of mathematical skills needed to calculate the stresses that would be experienced in a gun, to determine the thickness of the coils, and the actual dimensions to be machined so that outer coils would shrink onto inner coils and so pre-stress them, while at the same time expanding sufficiently so that heated outer coil could be slipped over an inner component. Range tables were calculated laboriously by hand or with primitive calculating machines.

The other thing to note is that these guns were still using Gunpowder – an explosive. The Mark 1 gun used pebble powder – gunpowder compressed into small cubes in an attempt to slow down the explosion and so reduce the rate of gas generation. The Mark II gun would use Prismatic gunpowder, where the explosive was formed into larger prisms, slowing down the rate of burning still further but also requiring a longer barrel to ensure all the powder was burnt before the shell left the barrel.

This animation was created using Cinema 4D, Quicktime and iMovie.
Music: Modern Situations by Unicorn hHeads

Handbook for the R.M.L 12.5 inch 38-ton Gun, Marks I and II, 1885
Treatise on the Manufacture of Guns and Text-Book of Service Ordnance, 1886
Treatise on the Construction and Manufacture of Ordnance in the British Service, 1877

Leave a Reply