BL 4 inch naval gun Mk II - VI

Ordnance BL 4 inch gun Mk I - Mk VI
Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1880s - 190?
Used by	United Kingdom
Specifications
Barrel length	Mk I 22.5cwt : 100 inches (2.540 m) bore (25 calibres) Mk II - VI : 108 inches (2.743 m) bore (27 calibres) 120 inches total
Shell	25 pounds (11.34 kg)
Calibre	4-inch (101.6 mm)
Breech	3-motion screw
Muzzle velocity	Mk I 13cwt : 1,180 feet per second (360 m/s) Mk II - VI : 1,900 feet per second (580 m/s)
Maximum firing range	Mk II-VI 7,700 yards (7,000 m)

The BL 4-inch gun Mk I - Mk VI were a family of early British breech-loading 4-inch naval guns.

This was the first 4-inch BL gun. With its short (60-inch total) barrel it had a range of only 5,500 yards.

With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards. Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891. Mk I 22.5 cwt continued to be used for training.

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.

Mk II guns and later Marks armed the following warships :

The gun was succeeded in its class from 1895 by the QF 4 inch gun Mk I.

A small number of these guns were converted to QF to use the same cartridges as the QF 4 in gun. They were designated Mk I/IV, I/VI etc. depending on which Mark of BL 4-inch had been converted. All had a bore of 27.85 calibres after conversion, with a muzzle velocity of 2,177 ft/second.

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