Japanese 30mm tracer round nerf

No Kiwi! J2M5 (30) is not historical yet. 😂
It still lacks 2x Type 99-2 and I’m quite sure 42rpg is also wrong. Long ago the load was bigger, until someone reported it with Type 2 data. The drum magazine in Type 2 had 42 round capacity, but Type 5 is belt fed. The two guns don’t have much in common. They don’t even fire the same cartridge. Unfortunately we don’t know what the ammo load was. Perhaps 60-100 like in other fighters.


What documentation is there for the J2M5 with 30 mm also having 20 mm cannons? Are they in the wings or is it the upward firing variety?

Yeah ik, they dont one tap anymore, are slower and less accurate. I feel like they do less damage than 20mms now. But what I really dont undestand that if the guns were only reason for high br why is the br same.

Yeah I also remember reading it was suposed to have 20mms too. Why would they even remove them fr? If ki-44 can change pair of 12mm for 40mm why couldnt J2M 20mm for 30mm with less ammo.

Duh, yeah it was the best round but half of the 30mms got it removed/replaced for AP and other half does not 1shot anymore. I would not care so much if it has slower muzzle velocity if its realistic but if I hit something with now slow and inaccurate shell I at least wanna destroy it and do more damage than 7.7mm ffs. Also German Me 163 30mms still oneshot unlike japanese ones. With Ki-200 begin higher br only because of the guns that does not work anymore yet its kept at higher br for no sane reason what so ever same with all the other japanese overtiered planes that have 30mm. . .

Some books simply mention that J2M5s with 30mm Type 5 cannos existed, without describing the full armament. Also there are few photos of a J2M5 with those fairings for 30mm guns. It’s very easy to think it had only those two Type 5s. Fortunately pair of documents mention the full armament and that J2M5 happens to be on one video.

2 and half years from the report already. Any visual model changes to old models take very long.


Yeah, same like they dont wanna give Ka-Mi floats.


I thought the upper one are the Army’s Ho-155 shells but seems like they are for the Navy’s Type 2 cannon.

So maybe the Ho-155 shell types are somewhat of a mystery.
Probably they used the same types as the 20mm Ho-5, which would be AP-T and HEFI.
I don’t think they would have used an explosive round without incendiary filler, since both Ho-103 and Ho-5 only ever used explosive-incendiary rounds.


That’s right about Ho-155 rounds. We know shell dimensions, types, weights and muzzle velocity, but nothing spefic about their contents. Now their fillers are still the same as Type 5 rounds. Known rounds are: AP, HEFI, special incendiary and hollow training round. It’s not even certain if the AP round had a tracer.

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According to the Aviation Ammunition and Handling Reference Book issued by the Inspectorate-General of Army Aviation in October 1944, the following are the ammunition belts in history.

No. 1 No. 2 No. 3 No. 4
12.7 mm Ho-103 MG Ma-102 Ma-103 AP-T
20 mm Ho-5 cannon Ma-202 HE-I HEI-T or AP-T
20 mm Ho-5 cannon Ma-202 AP-T HE-I HEI-T
30 mm Ho-155 cannon Ma-301 HE-I AP-T
37 mm Ho-203 cannon Ma-351 HE-I
37 mm Ho-204 cannon Ma-351 HE-I AP
57 mm Ho-401 cannon HE
  • “Ho-155” 30 mm Aircraft Cannon
    • HE Cartridge (Translator’s note: In the Japanese Army, even HE-I is called HE.)
      • The projectile has a Type 100 small instantaneous fuse in the nose, with the explosive and incendiary charge filling the rear of the fuse. There is a Type 40 blasting cap on the bottom of the cartridge. Complete round length is 190 mm. The projectile weight is 273 g. The muzzle velocity is 687 m/s.
    • Ma-301
      • This ammunition functions similarly to the Ma bullet for 12.7 mm MG and 20 mm cannon. The Ma-102 for 12.7 mm Ho-103 will detonate on duralumin plates 0.8 mm or thicker for destructive and incendiary effect. The Ma-201 for the 20 mm Ho-1/3 will detonate and incendiary effect with a duralumin plate of 3 mm or thicker. If the duralumin plate is less than 2 mm thick, it will not detonate and will penetrate.

Source: Jiro Sayama. Japanese Army Air Weapons. 2021. ISBN-13: 978-4769831976. pp. 508-528


Sad how even such detailed source doesn’t mention the fillers. At the very least it confirms the 30mm AP having a tracer element.

Moreover it reminds me of two things I had already forgotten:
-First we should report that training round they added to Ho-204. Even a solid AP round would be better if they can’t just copypaste some another Japanese 37mm APHE for it.
-Second we should find details about the HEI-T and Ma-202 rounds made for Ho-5. I think the latter is quite well known, but HEI-T not so much.


Sounds like that 30mm or 37mm fuzeless rounds would struggle to fuze properly on an aircraft.
It doesn’t say anything but obviously the sensitivity is also linked to impact velocity.
If the round gets too slow the impact force will simply be not enough to detonate the PETN in the nose.

The 20mm Ma-202 brass cap is around 1mm at the thinnest at the front, that of the 12.7mm Ma-102 around 0.75mm.

But interesting to see that they would mix the fuzeless rounds with fuzed.
I wonder if there was a any reason for that, other than to make sure that 50% of explosive rounds will definately fuze.

Maybe the idea was that a direct impact on armor from protected fuel tanks would perforate the plate with explosive force. Regular fuzed rounds would impact armor plates with their fuze with the explosive in the back, away from the plate. While the fuzeless rounds would act almost like HESH, with an explosion much closer to the armor plate.
But that’s probably not the reason, since 12.7mm HEI would have like no armor penetration power.

Other than that they really funtion more like incendiary rounds, since there would be little fragmentation from the thin brass nose piece.

The US and Hispano 20mm HEI rounds actual use a somewhat similiar fuze, though I imagine it to be more sensitiv. They also use a brass nose cap but it is filled with air, under which a detonator is placed.
The detonator will function from the nose getting crushed or deformed, by compressing the air inside.
Such detonator is probably more sensitive then unphlegmatized PETN.


Never heard about a Ho-5 HEI-T round 🤔

Since they had explosive tracers for all other Army 20mm cannons, it wouldn’t be far fetched.

The Ma-202 sits in the same boat as the Ma-102. Could be reported as missing round with some calculation to the actual filler, using the Ma-102 as reference.

But Gaijin would take like 3 years to implement it and then it would probably be useless anyway, since they can’t for the love of god, make ammo work, unless it explodes or penetrates.

It would probably just be a worse already existing fuzed HEI or not get implemented because of that.


I went through all Japanese ordnance related documents I had to find the HEI-T. One of them mislabelled Type 4 HEI round as HET and another document had just the “substitude HE-T”, which is the hollow training round. I was already quite sure the HE-T did not exist, but in the end I found it from CINCPAC Bulletin 85-45, Japanese Projectiles Vol 1.


Now I still need to figure out what the incendiary and igniting compounds in it were.
Perhaps we could have a HE only air targets belt with this?


Crazy :D

Why? It says, 2.5g RDX. That’s good enough for the game.

The incendiary compound is probably the same as the Ma-102, and Ma-103s, consisting of Flashpowder made from Barium Nitrate, Aluminum and Magnesium.


Imgur: The magic of the Internet

The igniting compound probably refers to what actually ignites the tracers, probably something with a delay to prevent the pilot from getting blinded at night.

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I hope that we finally get custom ammo belts :)

Well and that explosive shells stop dealing crazy damage to structure while armor plates actually requiring 20mm cannons to be reliably defeated.

For going after B-17s you can probably just stick with HEI and HEI-T, since AP-T will have different ballistics at long range anyway, throwing off the aim for HEI.


Yes most likely the explosive amount won’t make a difference anyway and indeed the igniting compound has to be for tracer, since the AP-T also has 1g. I only noticed that now.

I’d still like to find precise data about the fuse. It is the same Type 2 fuse as in the HEFI round. This says it should have 3.4 gm filler, but in game we have 4.53 gm. I think it was slightly changed last year, so there should be a report about it somewhere.

Okay forget the earlier. I was looking at the wrong round and now I found the fuse. The one we have in game has 3.96893g filler and 0.56699g fuse, which make 4.53g. With the same fuse we get 3.06g for the HEFI-T round.

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They changed the round to the model with the two piece fuze that had a gain inside the fuze instead of being threaded to it. Thus the later model carried more RDX.
Of course the fuze carries less explosive in the gain but in general the explosive in the fuze is general ignored by the Devs.

Would you mind sharing that page with Ho-5 belts? It could help with the suggestion.


Here is the source book. Please use this in your reports and suggestions. If other pages are needed I will add them.


October 1944, Inspectorate-General of Army Aviation, “Reference for Handling of Aircraft Cannon Ammunition (Top Secret)”
昭和十九年十月 陸軍航空総監部 「航空機関砲弾薬取扱ノ参考極秘」

“Ho-5” 20 mm cannon various ammunitions
Type 2 HE-I, Type 2 HEI-T, Type 2 AP-T

Ammunition Belts
(It has already been translated, so it will be omitted.)