[1] With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards.

[1] Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891.

The improved 27-calibre Mk II gun and subsequent Marks, often referred to as 4 inch 26 cwt, replaced the early Mk I versions in service.

The longer barrel (108 inch bore : 27 calibres) gave it a range of 7,700 yards.

All had a bore of 27.85 calibres after conversion, with a muzzle velocity of 2,177 ft/second.