Britain
8"/50 (20.3 cm) Marks IX and X
Updated 18 February 2009
Intended for a new class of heavy cruisers during World War II which never made it beyond the sketch design stage.

The Mark IX* was to the older design standards, being of built-up construction with an A tube, jacket, breech ring and breech bush and would have been about the same weight as the 8"/50 (20.3 cm) Mark VIII.  It would also have used the same breech as the Mark VIII with slight modifications.  On relining with a tapered inner A tube, it was to have become the Mark IX.  One gun was ordered from Vickers-Armstrong in April of 1941.

This prototype was abandoned when new design guidelines were adopted.  Under the new rules, which were based upon Vickers-Armstrong's practice, stresses up to 24/27 of the yield point were now allowed rather than the prior standard of 20/27 of the yield point.

The Mark X* was designed to the new rules and would have had similar components as the Mark IX* but was now of lighter construction and had a new breech mechanism.  This gun would have been designated as the Mark X after being relined with a tapered inner A tube.  None of these guns were ever built and the order was cancelled in October 1942 along with the cruisers that would have carried them.
.
Gun Characteristics
.
Designation 8"/50 (20.3 cm) Marks IX and X
Ship Class Used On Proposed cruisers of World War II
Date Of Design 1941
Date In Service None built
Gun Weight Mark IX:  17.04 tons (17.3 mt)
Mark X:  12.5 tons (12.7 mt)
Gun Length oa 413.25 in (10.497 m)
Bore Length 400.0 in (10.160 m)
Rifling Length 346.3 in (8.796 m)
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume 4,300 in3 (70.46  dm3)
Rate Of Fire about 3 - 4 rounds per minute
.
Ammunition
.
Type Bag
Projectile Types and Weights SAPC - 290 lbs. (131.5 kg)
HE - 256 lbs. (116.1 kg)
Bursting Charge SAPC - 11.5 lbs. (5.2 kg)
HE - about 23 lbs. (10 kg)
Projectile Length SAPC - 36 in (91.4 cm)
HE - N/A
Propellant Charge 72.25 lbs. (32.77 kg) SC 205
Muzzle Velocity 2,670 fps (814 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
Note:  The SAPC rounds were to a new longer and heavier design than those for the earlier Mark VIII guns.
.
Range
.
Elevation With 290 lbs. (131.5 kg) SAPC Shell
Range @ 5.2 degrees 10,000 yards (9,140 m)
Range @ 9.9 degrees 15,000 yards (13,720 m)
Range @ 16.3 degrees 20,000 yards (18,290 m)
Range @ 25.4 degrees 25,000 yards (22,860 m)
Range @ 43.9 degrees 30,000 yards (27,430 m)
Range @ 45.0 degrees 31,300 yards (28,620 m)
Note:  Time of flight for SAPC Shell with MV = 2,600 fps (792.5 mps)
   10,000 yards (9,140 m): 14.3 seconds
   15,000 yards (13,720 m):  24.4 seconds
   20,000 yards (18,290 m):  37.1 seconds
   25,000 yards (22,860 m):  53.6 seconds
   30,000 yards (27,430 m):  81.9 seconds
.
Mount / Turret Data
.
Designation Three-gun Turrets
   All designs (3):  N/A (probably Mark III)
Weight  N/A
Elevation -3 / +45 degrees
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate N/A
Gun recoil N/A
Loading Angle N/A
.
Data from
"Naval Weapons of World War Two" by John Campbell
"British Cruisers of World War Two" by Alan Raven and John Roberts
Page History

06 November 2006 - Benchmark
18 February 2009 - Added additional construction details