4.5-inch Mark 8 naval gun
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The 4.5 inch Mark 8 is a British naval gun system which currently equips the Royal Navy's destroyers and frigates, and some British destroyers and frigates sold to other countries. Wikipedia
Shell: 113 x 700mmR; Fixed QF 46 pounds (21 kg) HE
Barrel length: 244.75 inches (6.217 m) bore (55 calibres)
Calibre: 4.45-inch (113 mm)
In service: 1972–present
Maximum firing range: 27.5 kilometres (17.1 mi)
Rate of fire: 25 rounds per minute automatic