The 10-inch gun was a standard "Woolwich" design 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 or 2 coils ; 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 Mk I guns were made.
Ammunition
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. The gun's primary projectile was "Palliser" shot or shell, an early armour-piercing projectile for attacking armoured warships. A large "battering charge" of 70 pounds "P" or 60 pounds "R.L.G." gunpowder was used for the Palliser projectile to achieve maximum velocity and hence penetrating capability. Common shells and shrapnel shells were fired with the standard "full service charge" of 44 pounds "P" or 40 pounds R.L.G. gunpowder, as for these velocity was not as important.
One 10-inch Mk I Common Shell, one 10-inch Mk II Common Shell & one 10-inch Mk IIIPalliser Shot as part of the Victorian Navy display at the Geelong Maritime Museum, Australia. Various other guns are mounted or unmounted in Bermuda, with some lying outside of Fort St Catherine, having been rolled out when made obsolete, and a number having been found buried in the moat of Fort Cunningham. Three have been erected on concrete display stands at Fort Hamilton, though the original mounts are missing, and another at Alexandria Battery.
