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Quick facts for kids Ordnance BL 4-inch gun Mk I – Mk VI |
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| 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 |
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| 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 Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891.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-inch 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.
