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Japanese Explosive Ordnance – Army Ammunition – Navy Ammunition |
Chapter 5 - Section 1 |
NAVY PROJECTILES |
Type 99 - 20-mm Ammunition |
Naval 20-mm ammunition is divided into two classes: Type 99 Mk I and Type 99 Mk II. The two are distinguished by the fact that the Mk I uses a small-size cartridge case (3.79 in.), and the Mk II uses a large-cartridge case (3.98 in.). |
Both sizes use the same projectiles and fuzes, but there are a greater number of types and modifications of rounds in the smaller size. |
This ammunition is a Japanese copy of the Swiss Oerlikon design. In addition to rounds of Japanese make, some of Swiss orgin have been used by the Japanese. |
Case |
Mk I |
Mk II |
|
Length |
3.79 inches |
3.98 inches. |
|
Diameter at base |
0.75 inch |
0.75 inch. |
|
Weight (empty) |
57.0 grams |
71.0 grams. |
|
Material |
Brass |
Brass. |
The cases are of the reduced-rim type and are crimped to the projectiles by either three or six crimps at the cannelure, and sealed with a clear lacquer. |
Propellant: The propellant from the Japanese-manufactured rounds is graphited, single- base, single perforated, cylindrical, nitrocellulose grains. The propellant from the Swiss rounds is single-base, graphite-coated, nitrocellulose grains, in the form of flakes. The Mk I case contains 13.6 grams of propellant and the Mk II case contains 21.4 grams of propellant. |
Projectiles: In the case of Japanese manufactured ammunition, the type of projectile is indicated by painting the projectile body a solid color. Subsequent modifications of the original type are indicated by one or more white bands around the projectile body, thus: |
Original type: No bands. |
Modifiaction 1: One 5-mm white band. |
Modification 2: Two 5-mm white bands. |
Modification 3: Three 5-mm white bands. |
Modification 4: One 10-mm white band. |
All the Swiss projectiles are painted a solid color without bands. |
The following dimensions are common the all projectiles: |
Distance from rotating band to bourrelet, 1.29 inches. |
Distance from rotating band to base, 0.36 inch. |
Diameter of body, 0.77 inch. |
Diameter at bourrelet, 0.79 inch. |
Diameter at base, 0.75 inch. |
Diameter at rotating band, 0.83 inch. |
Figure 349 – Type 99 20-mm Ammunition. |
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