RML 10 inch 18 ton gun

Ordnance RML 10 inch 18 ton gun
Mk I gun on broadside ironclad HMS Sultan in the 1890s
Type	Naval gun Coastal gun
Place of origin	United Kingdom
Service history
In service	1868 - 19??
Used by	Royal Navy Australian Colonies
Wars	Bombardment of Alexandria (1882)
Production history
Designer	M Robert Fraser, Royal Gun Factory
Designed	1868
Manufacturer	Royal Arsenal
Unit cost	£1006
Variants	Mks I - II
Specifications
Barrel length	145.5 inches (3.70 m) (bore)
Shell	400 to 410 pounds (181.4 to 186.0 kg) Palliser, Common, Shrapnel
Calibre	10-inch (254.0 mm)
Muzzle velocity	Palliser : 1,364 feet per second (416 m/s) Common & shrapnel : 1,028 feet per second (313 m/s)
Maximum firing range	6,000 yards (5,500 m)

The RML 10 inch guns Mk I - Mk II were large rifled muzzle-loading guns designed for British battleships and monitors in the 1860s to 1880s. They were also fitted to the Bouncer and Ant-class flat-iron gunboats. They were also used for fixed coastal defences around the United Kingdom and around the British Empire until the early years of the 20th Century.

The 10-inch gun was a standard "Woolwich" design (characterised by having a steel A tube with relatively few broad, rounded and shallow rifling grooves) developed in 1868, based on the successful Mk III 9-inch gun, itself based on the "Fraser" system. The Fraser system was an economy measure applied to the successful Armstrong design for heavy muzzle-loaders, which were expensive to produce. It retained the Armstrong steel barrel surrounded by wrought-iron coils under tension, but replaced the multiple thin wrought-iron coils shrunk around it by a single larger coil (10 inch Mark I) or 2 coils (Mark II); the trunnion ring was now welded to other coils; and it eliminated Armstrong's expensive forged breech-piece.

The gun was rifled with 7 grooves, increasing from 1 turn in 100 calibres to 1 in 40.

It was first used for the main armament on the central battery ironclad HMS Hercules, completed in late 1868.

A number of the Mk I guns on HMS Hercules and one of the two damaged guns in HMVS Cerberus suffered from cracked barrels. Presumably this is why only a few (at least 25) Mk I guns were made.

When the gun was first introduced projectiles had several rows of "studs" which engaged with the gun's rifling to impart spin. Sometime after 1878, "attached gas-checks" were fitted to the bases of the studded shells, reducing wear on the guns and improving their range and accuracy. Subsequently, "automatic gas-checks" were developed which could rotate shells, allowing the deployment of a new range of studless ammunition. Thus, any particular gun potentially operated with a mix of studded and studless ammunition.