# 12.7mm Ho-103 ammunition



## Laurelix (Oct 5, 2019)

12.7mm Ho-103 / Type 1 12.7mm
Cartridge: (12.7mm x 81SR)
Rate of Fire: 900RPM / 400RPM (Synchronised)
Muzzle Velocity: 780m/s







AP - (Italian)
Fused HE-I (Italian)
AP-T (Japanese)
Fuzed HE-I / Ma103 (Japanese)
Fuzeless HE-I / Ma102 (Japanese)

Ho-103 was compatible with Breda-Safat since it’s the same cartridge

• Type 1 AP-T
- Projectile Mass: 36.50 g
- Muzzle Velocity: 780 m/s
- Armour Penetration: 12 mm at 300 m, 10 mm at 700 m
[Penetration according to Mr. Yasufumi Kunimoto who is a famous researcher of Japanese weapons.]

If Yasufumi is correct the ballistics would look roughly like this:
780m/s at 10m
650m/s at 300m
570m/s at 700m


• Ma-103 Fuzed HE-I
- Projectile Mass: ~ 36.59 g
- Muzzle Velocity: 780 m/s
- Explosive type: RDX + Incendiary
- Explosive mass: ~ 0.6 g + 1.45 g
(Barium Nitrate dominated incendiary)


• Ma-102 Fuzeless HE-I
- Projectile Mass: ~ 36.30 g
- Muzzle Velocity: 780 m/s
- Explosive type: RDX + PETN + Incendiary
- Explosive mass: ~ 0.96 g + 0.96 g + 1.46 g
(Barium Nitrate dominated incendiary)

Any gun with bigger calibre than 10mm is classed as a cannon by the Japanese

More Info:
RDX = 1.6x effectiveness factor vs TNT
PETN = 1.66x effectiveness factor vs TNT

Ma-102 TNT equivalent explosive power
= (0.96 x 1.6) + (0.96 x 1.66)
= 1.54g + 1.59g
= 3.13g TNT equivalent explosive power

This is one deadly bullet considering it has 50% the explosive power of 20mm Hispano at higher rate of fire + 1.46g of incidiary that is mostly Barium Nitrate.
By removing the fuze it allowed the Japanese to create a round that holds far more explosive and incendiary power.

In the book by Edward M. Young, B-24 Liberator vs Ki-43 Oscar: China and Burma 1943 its stated that the Ki-43’s which only had 2x 12.7mm cannons in the nose (synchronised at 400RPM RoF) and only 270 rounds per gun were successfully downing B-24 Liberators. In fact the B-24 crews reported that they were getting shot at by 20mm cannons from A6M Zeros which infact they were just Ki-43’s shooting .50 cals. On average it took 80-90 rounds from Ho-103 to down a B-24 Liberator.

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## taly01 (Oct 11, 2019)

Ma-102 probably was first available from late 1943 from quotes of Japanese pilots in late 1943 in the "MacArthurs Eagles" Book. However one also says they had shortages of it and had to use the "less effective" earlier types.

Look at Page 34 Japanese_air_weapons_and_tactics.pdf for USSBS analysis of it.


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## KillaKiwi (Nov 27, 2021)

Laurelix said:


> In the book by Edward M. Young, B-24 Liberator vs Ki-43 Oscar: China and Burma 1943 its stated that the Ki-43’s which only had 2x 12.7mm cannons in the nose (synchronised at 400RPM RoF) and only 270 rounds per gun were successfully downing B-24 Liberators. In fact the B-24 crews reported that they were getting shot at by 20mm cannons from A6M Zeros which infact they were just Ki-43’s shooting .50 cals. On average it took 80-90 rounds from Ho-103 to down a B-24 Liberator.



They probably thought they were shot by 20mm cannons from the explosion of the rounds and not that they had the effect of 20mm cannons on the plane.
I'm not sure how 80-90 rounds on average to down a B-24 is supposed to be a good number.
If I'm not mistaken did WW2 pilots in general land around 5% of their shots on target, which means that even if pilots could land 10% of all shots fired they still would land barely more than half the rounds required to shot down a B-24.

If the guns were really that slow synchronised (400 RPM), it also would take 40 seconds to empty them while the plane is under constant fire from 12.7mm guns itself with 750 RPM each, possibly from multiple B-24 flying in formation.

Honstely sounds like suicide to attack a B-24 with just two 12.7mm MGs. Sure they are not harmless but it's like trying to take down an elephant with a 9mm pistol.

I can't imagine the amount of Ki-43 shot down for a few B-24 that they could destroy in return.



Laurelix said:


> • Ma-102 Fuzeless HE-I
> - Projectile Mass: ~ 36.30 g
> - Muzzle Velocity: 780 m/s
> - Explosive type: RDX + PETN + Incendiary
> - Explosive mass: ~ 0.96 g + 0.96 g + 1.46 g


Not sure were the explosive figure comes from but from the volume of the shell minus the brass liner, the explosive amount can't be much more than 1.4g.
Incendiary filler generally has a greater density so it's pretty unlikely that the shell contained more explosive than incendiary comparing the volume of the two.


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