BL 12-inch Mk X naval gun
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The BL 12 inch Gun Mark X was a British 45-calibre naval gun which was mounted as primary armament on battleships and battlecruisers from 1906. It first appeared on HMS Dreadnought. Wikipedia
Barrel length: 45 feet (13.72 m) bore (45 cal)
Breech: Welin interrupted screw
Calibre: 12 inches (304.8 mm)
In service: 1906 – 1923
Maximum firing range: 22,860 m (25,000 yd)
Muzzle velocity: 2,700 ft/s (823 m/s)