BL 6 inch 80 pounder gun

Ordnance BL 6 inch 80 pounder Mk I
Gun from HMAS Protector at Birkenhead, South Australia, August 2011
Type	Naval gun Coast defence gun
Place of origin	United Kingdom
Service history
In service	1880 - 1943
Used by	Royal Navy Australian Colonies
Production history
Designer	Elswick Ordnance Company
Manufacturer	Elswick Ordnance Company
Variants	Mk I
Specifications
Weight	80 or 81 cwt (4 tons)
Barrel length	153 - 156 inches
Shell	80 pounds (36.29 kg) Palliser, Shrapnel, common
Calibre	6-inch (152.4 mm)
Breech	3 motion interrupted screw. Elswick cup obturation
Muzzle velocity	1,880 feet per second (573 m/s)
Maximum firing range	8,000 yards (7,300 m)

The BL 6 inch 80 pounder gun Mk I was the first generation of British 6-inch breechloading naval gun after it switched from muzzle-loaders in 1880. They were originally designed to use the old gunpowder propellants.

Mk I of 80 cwt (4 tons) as originally built was an Elswick Ordnance design which was weakly made and fired only an 80-pound (36 kg) projectile. It consisted of a steel barrel with wrought-iron coils shrunk over it. A few guns were issued to the Royal Navy but most were replaced by the later versions. Mk I guns remaining in British service were rebuilt with "chase hoops" added around the barrel for strengthening, and the barrel was shortened by 3 inches to keep its centre of gravity at the trunnions. This resulted in the 81 cwt Mk I gun.

The breech was rotated to the left to lock it, unlike standard British service BL guns made by the Royal Gun Factory which all rotated to the right to lock.

These guns are commonly referred to as "6-in. 81-cwt B.L.R." in contemporaneous publications such as Brassey's Naval Annual. The official designation in British ordnance manuals was "80-pounder BL" to differentiate it and its ammunition from the later marks of 6-inch BL guns which fired 100-pound projectiles.

Australian colonies and New Zealand purchased various 6-inch guns direct from the manufacturers, usually Elswick Ordnance Company, and these versions do not correspond directly with the official "Marks" as adopted by the British government. Specifications of guns purchased by Australian colonies are similar to those of the original British Mk I 80 cwt gun, firing an 80-pound projectile.

The gun equipped some gunboats of the Australian colonial navies :

Also on armed harbour vessels in Victoria :