United States of America
8"/30 (20.3 cm) Marks 1 and 2
Updated 27 August 2006
One of the first heavy guns of the "New Navy."

Mark 1 consisted of A tube, jacket, 19 hoops and an elevating band with integral trunnions.  Mark 1 Mod 1 had no trunnions.  The Mark 2 was similar, but had the hoops differently arranged, did not have integral trunnions and had its rear sights controlled by worm and miter gears.
WNUS_8-30_mk1_Boston_pic.jpg

8"/30 (20.3 cm) on USS Boston in 1888
An open-back shield was later added to this gun
Note the Gatling machine gun in the upper left corner and the 37 mm revolver cannon on the right
Detail from U.S. Naval Historical Center Photograph # NH 56537
WNUS_8-30_mk1_Atlanta_stern_pic.jpg

After 8"/30 (20.3 cm) on Atlanta circa 1886
An open-back shield was later added to this gun
U.S. Naval Historical Center Photograph # NH 57410
WNUS_8-30_mk1_Chicago_gun_pic.jpg

Breech of 8"/30 (20.3 cm) on USS Chicago
Detroit Publishing Company Collection Photograph
Library of Congress Photograph ID LC-D4-20303
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Gun Characteristics
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Designation 8"/30  (20.3 cm) Marks 1 and 2
Ship Class Used On Atlanta and Chicago Classes
Date Of Design about 1883
Date In Service 1886
Gun Weight 29,100 lbs. (13,200 kg) not including breech
Gun Length N/A
Bore Length 240 in (6.096m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist Increasing RH 1 in 180 to 1 in 30 at the muzzle
Chamber Volume N/A
Rate Of Fire about 0.5 - 1 round per minute
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Ammunition
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Type Bag
Projectile Types and Weights AP - 260 lbs. (118 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge 49.6 lbs. (22.5 kg)
Muzzle Velocity 2,000 fps (610 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
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Range
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Elevation With 260 lbs. (118 kg) AP Shell
Range @ 20 degrees about 14,000 yards (12,800 m)
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Mount / Turret Data
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Designation Single Barbette Mount
   Atlanta (2):  Mark 1

Single "Half-turret"
   Chicago (4):  Mark 2
Weight  N/A
Elevation -5 / +20 degrees
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate N/A
Gun recoil N/A
Loading angle N/A
Notes:

1) These mounts were steam powered.

2) The Mark 2 "half-turret" was a cylindrical shield with a top but no back.
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Data from
"US Naval Weapons" and "US Cruisers:  An Illustrated Design History" both by Norman Friedman