12.7mm Ho-103 ammunition

[Laurelix]

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.

 

[taly01]

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.

 

[KillaKiwi]

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.

• 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.]

This checks out with German data on the British 12.7x81mm AP round being quoted with 15mm penetration at 100m and 11mm at 300m against high hardness plates.

• 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.
(Edit: I saw how you came up with those numbers and I guess they are more or less correct)
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.

However there are some errors. The Ma 102 weighed around 32.9g (shown in the image you provided) and probably had a higher muzzle velocity than the standard ammo, due to being lighter and using more powder.

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.

Not really comparable:
Ho-103 -> 32.9g, +800m/s, ~1.9g Explosive, 1.46g Incendiary mixture
Hispano -> 129g, 853m/s, 5.6g Explosive, 5.5g Incendiary mixture

Two 12.7mm Ma-102 still won't bring the same amount of explosive and incendairy into the target while the Hispano produces effective fragments and the incendiary can can reach deeper inside the plane before burning up.

The fuzeless Ma-102 is just a slight improvement over the fuzed Ma-103, which in itself was just an ordinary .50cal explosive-incendiary round.