British 4"/50 (10.2 cm) BL Mark VII

British
4"/50 (10.2 cm) BL Mark VII
Updated 19 July 2006

This weapon entered service on HMS Bellerophon and later replaced many of the 4"(10.2 cm) Mark I and Mark III guns used on previous Dreadnoughts.

These weapons were installed in both casemates and in single open mounts on early British dreadnoughts. The open mounts were installed without shields but some ships had these added after 1917. In 1918 a HA mounting using a reduced charge was introduced and most capital ships had one or two of these installed on a main caliber turret for anti-aircraft purposes.

During World War II these weapons were used on many minor warships and a considerable number were used as coastal artillery.

Constructed of inner A and A tubes, wire wound, B tube to the muzzle with jacket, breech ring and breech bush screwed into the A tube. Used a Welin breech block with "pure couple" breech mechanism. Cannelured rings for reducing "steel choke" were placed between the shoulders of the A and inner A tubes. Firing could be either percussion or electrical. A total of 700 of these weapons were produced, of which 482 still remained in 1939.

HMS Vanguard
4"/50 (10.2 cm) guns in superstructure and on "X" turret, the latter were not HA mountings

HMS Thunderer showing superstructure 4"/50 (10.2 cm) guns
Photograph copyrighted by D.K. Brown

Gun Characteristics .

Designation	4"/50 (10.2 cm) BL Mark VII, VII and VIII*
Ship Class Used On	Bellerophon, St. Vincent, Neptune, Indefatigable, Colossus, Orion, Lion and King George V (1910) classes Boadicea, Active and Bristol light cruiser classes plus smaller warships Indomitable as rearmed During World War II this weapon was used mostly on DEMS
Date Of Design	About 1904
Date In Service	1908
Gun Weight	4,687 lbs. (2,126 kg)
Gun Length oa	208.5 in (5.295 m)
Bore Length	201.3 in (5.112 m)
Rifling Length	171.6 in (4.359 m)
Grooves	32
Lands	N/A
Twist	Uniform RH 1 in 30
Chamber Volume	600 in³ (9.83 dm³)
Rate Of Fire	about 6 - 8 rounds per minute

Ammunition .

Type	Bag
Projectile Types and Weights	HE - 31 lbs. (14.06 kg) CPC - 31 lbs. (14.06 kg) Shrapnel - 31 lbs. (14.06 kg)
Bursting Charge	N/A
Projectile Length	N/A
Propellant Charge	World War I: 9.37 lbs. (4.3 kg) MD16 World War I HA: 6.0 lbs. (2.7 kg) MD8 World War II: 9.7 lbs. (4.4 kg) SC103
Muzzle Velocity	2,864 fps (873 mps) With HA charge: about 2,400 fps (732 mps)
Working Pressure	N/A
Approximate Barrel Life	N/A
Ammunition stowage per gun	N/A
Note: Shells were 3crh.

Range .

Elevation	With 31 lbs. (14.1 kg) HE Shell
Range @ 15 degrees	11,600 yards (10,610 m)

Mount / Turret Data .

Designation	Single Mounts: PII, PII, PIV, PIV** and PVIII Bellerophon (16), St. Vincent (20), Neptune (16), Indefatigable (16), Orion (16), Lion (16) and King George V (16) HA Mark II
Weight	N/A
Elevation	PII, PII* and PVI: -7 / +15 degrees PIV, PIV* and PVIII: -10 / +15 degrees HA Mark II: -10 (?) / +60 degrees
Elevation Rate	Manually operated, only
Train	Open mounts: 360 degrees Casemate mounts: About +30 to +150 degrees
Train Rate	Manually operated, only
Gun recoil	N/A

Data from
"The Grand Fleet: Warship Design and Development 1906-1922" by D.K. Brown
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 17" article in "Warship Volume X" both by John Campbell
"British Battleships 1860 - 1950" by Oscar Parkes
"Battlecruisers" by John Roberts
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