Monday, 14 September 2015

Imperial Japanese Navy Ammunition - 20mm Projectiles


Imperial Japanese Navy Ammunition

Type 99 20mm Ammunition

 

Naval 20mm 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-size 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 origin have been used by the Japanese.
 
Case  -----  Mk I ------ Mk II
Length ----- 3.79 in ----- 3.98 in
Diameter at base ----- 0.75 in ----- 0.75 in              
Weight (empty) ----- 57 grams ----- 71 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
Modification 1: One 5mm white band
Modification 2: Two 5mm white bands
Modification 3: Three 5mm white bands
Modification 4: One 10mm white band
 
All the Swiss projectiles are painted a solid color without bands.
 
The following dimensions are common to 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 rotating band - 0.83 inch




20mm High-Explosive Projectile

 
Weight of projectile (fuzed): 4.5 oz
Length of projectile (fuzed): 3.23 inches

Length of complete round:
-Mk I: 5.66 inches
-Mk II: 6.84 inches

Filling: Pentolite (50 percent TNT, 50 percent PETN)
Weight of filling: 0.35 oz

Fuzing:
Japanese: Model 2
Swiss: Model 1

Color and markings:
Japanese: Rust brown overall (modifications indicated by white bands)
Swiss: 1. Yellow overall   2. Dark Brown overall

Remarks:
Ammunition of Swiss manufacture has been found to contain slightly more explosive than the Japanese round.


20mm High-Explosive Incendiary Projectile


Weight of projectile (Fuzed): 4.51 oz
Length of projectile (Fuzed): 3.23 inches

Length of complete round:
-Mk I: 5.66 inches
-Mk II: 6.84 inches

Filling:
-TNT: 0.18 oz
-WP: 0.11 oz
-Incendiary Mixture: 0.04 oz

Fuzing:
-Basic Projectile: Model 1
-Modification I: Model 1
-Modification II: Model 3
-Modification III: Model 2
-Modification IV: Model 3

Colors and markings:
Greenish-Yellow overall, with one or more white bands to indicate modifications.

Remarks:
The body of all projectiles (basic and modifications) is of steel, with one cavity.  The base of the cavity contains TNT, above which is an aluminum cannister containing white phosphorus.  The cannister is surrounded by a graphited, flake nitrocellulose incendiary mixture.  The Model 4 projectile eliminates the TNT and has a longer white phosphorus cannister.

Differences between the basic projectiles and subsequent modifications are principally in the fuzes and slight changes in the shape of the cavity.





20mm High-Explosive Tracer Projectile
 

Weight of projectile (Fuzed): 4.51 oz
Length of projectile (Fuzed): 3.1 inches
 
Length of complete round:
-Mk I: 5.7* inches
-Mk II: 6.88 inches
 
Filling: Pentolite (50 percent TNT, 50 percent PETN)
Weight of filling: 0.18 oz

Fuzing:
-Basic Projectile: Model 1
-Modification I: Model 1
-Modification II: Model 3
-Modification III: Model 2
-Modification IV: Model 3
-Modification V: Two-piece fuze (Japanese designation unknown)

Color and markings:
Red overall (modifications indicated by white bands)

Remarks:
The body of all these projectiles (basic and five modifications) contains two cavities separated by a steel septum.  The upper cavity contains the H.E. filling, while the lower contains the tracer.  The same H.E. filling and tracer mixture are used in all instances.  

Differences between the basic projectile and subsequent modifications are principally in the fuzes and weight of H.E. and tracer filling used.

*The No. Model and Model 1 projectiles are 0.16 inch shorter than the other rounds.



20mm High-Explosive Tracer (Self-Destroying) Projectile
 


Weight of projectile (Fuzed): 4.5 oz
Length of projectile (Fuzed): 3.15 inches

Length of complete round:
-Mk I: 5.58 inches
-Mk II: 6.76 inches

Filling: Pentolite (50 percent TNT, 50 percent PETN)
Weight of filling: 0.15 oz

Fuzing: Model 1

Color and markings:
Japanese: Red overall
Swiss: Black overall

Remarks:
The projectiles are similar to the H.E. tracer types except for their self-destroying feature, which is accomplished by  a hole drilled through the septum of the projectile.  A black-powder train leads from the tracer, through the hole in the septum and the H.E. filling, to the base of the gaine.


20mm Armor-Piercing Incendiary Projectile

 

Weight of projectile: 4.64 oz
Length of projectile: 3.15 inches

Length of complete round:
-Mk I: 5.58 inches
-Mk II: 6.76 inches

Filling: Incendiary mixture
- Nitrocellulose: 77.5%
- Sodium Nitrate: 11.3%
- Aluminum: 11.2%

Weight of filling: 0.12 oz

Fuzing: None

Color and Markings: White overall

Remarks:
The projectile is unfuzed and has a pointed steel body and a soft copper cap soldered to the nose.  The incendiary filling loaded through the base is sealed with a threaded base plug.

Upon impact, the rear end of the projectile ruptures and the heat generated ignites the incendiary filling.

No modifications or similar Swiss ammunition exist.



20mm Tracer Projectile


Weight of projectile: 4.44 oz
Length of projectile: 3.23 inches
Length of complete round:
-Mk I: 5.66 inches
-Mk II: 6.84 inches
 
Filling: Tracer mixutre
Weight of filling: 0.31 oz
 
Fuzing: None
 
Color and Markings: Red overall (modifications indicated by white bands)
 
Remarks:
The projectile is unfuzed; has a blunt nose and a long cavity containing the tracer-element. It is loaded so as to be the first round fired to break the muzzle cover.  It is, therefore, often referred to as a "bag-buster".

In addition to the basic Japanese type, Modifications II and III exist, as well as a similar round of Swiss make.  The weight of tracer constitutes the difference in the Japanese modifications.



20mm Practice Projectile
 


Weight of projectile: 4.45 oz
Length of projectile: 3.23 inches

Length of complete round:
-Mk I: 5.66 inches
-Mk II: 6.84 inches

Filling: None

Fuzing: None

Color and Markings: Black overall

Remarks:
The projectile is unfuzed and has a blunt nose.  It has an empty cavity which is closed at the base with a crimped steel plug.  No modifications exist.



Next Time: 25mm Projectiles

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