Mark II had an enlarged powder chamber and attained higher muzzle velocity and slightly longer range.

It was succeeded in its class on new battleships by the BL 12 in (30 cm) Mk II gun.

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.

[5] By this time the gun no longer fired studded ammunition without gas-checks.