The 'ideal' WW2 20mm cannon rounds (discussion)

[ThatZenoGuy]

Making this thread because I like WW2 stuff and I want to hear people's viewpoints on the matter.
WW2 ammunition for 20mm cannons came in many varieties, with special national flavors across the globe. I'll explain the knowledge I know thus far. Because it's a fair bit of writing I'll add other types of rounds later.

Explosive rounds

HE/HEF=Your bog standard explosive cannon projectiles, sometimes called HE, sometimes HEF (high explosive fragmentation), even if both do the same thing. They explode, and launch fragments everywhere. They can have a tracer installed at the cost of explosive filling.
Pros
-Simple, cost effective
-In theory some increase in firestarting with the right explosive mixtures
-Fuze lets you have delayed detonation for added damage
Cons
-Basically no armor penetration capability
-Fuze increases price of ammunition compared to AP rounds
-Average damage for a HE round

HEI/HEFI=Basically the above, but replacing some of the explosive filler with incendiary instead, this is scattered about the plane when the explosives detonate. A lot of nations used these munitions.
Pros
-Much of the same as HEI, but higher chance of starting fires
Cons
-Again much of the same, but low damage for a HE round

HE(minengeschoss)=A weird munition used by Germany and possibly Japan. Using drawn steel like a cartridge to maximize explosive filler at the expense of steel that could produce larger fragments. Apparently very effective and used in some post-war cannons, but difficult to produce.
Pros
-Massive explosive payload for a HE round
-Potential for explosive charge to convert some of the target structure into fragments
-Fuze had delay from the start
-Explosive filler was replaced with one more capable of starting fires
Cons
-Expensive, the fuze and drawing process was not easy
-Low quality ballistics, projectile was relatively light weight for it's diameter
-Basically no armor penetration capabilities
-Smaller fragments due to thin shell wall

HE/HEI(Fuzeless)=A weird creation by a desperate Japan, in this design the fuze was omitted entirely. This allowed for more HE payload for it's size, while keeping a thick fragment producing shell wall. But it also meant the shell's ability to have a delayed explosion was stunted. Alternatively this round could have both HE and incendiary filling without compromising explosive payload
Pros
-Dirt cheap, no fuze makes it very easy to produce
-Large explosive payload for a HE round, although inferior to Minengeschoss, average payload if using incendiary as well
-Good fragment producing capabilities
Cons
-No fuze delay, damage is inherently limited as the projectile cannot pierce the skin as much as other rounds because it is fuzed by impact
-Potential safety concerns, Japan marked them with special colors to warn crews to be careful

Feel free to add any information you know of. ;D

 

[49ersfootball]

Making this thread because I like WW2 stuff and I want to hear people's viewpoints on the matter.
WW2 ammunition for 20mm cannons came in many varieties, with special national flavors across the globe. I'll explain the knowledge I know thus far. Because it's a fair bit of writing I'll add other types of rounds later.

Explosive rounds

HE/HEF=Your bog standard explosive cannon projectiles, sometimes called HE, sometimes HEF (high explosive fragmentation), even if both do the same thing. They explode, and launch fragments everywhere. They can have a tracer installed at the cost of explosive filling.
Pros
-Simple, cost effective
-In theory some increase in firestarting with the right explosive mixtures
-Fuze lets you have delayed detonation for added damage
Cons
-Basically no armor penetration capability
-Fuze increases price of ammunition compared to AP rounds
-Average damage for a HE round

HEI/HEFI=Basically the above, but replacing some of the explosive filler with incendiary instead, this is scattered about the plane when the explosives detonate. A lot of nations used these munitions.
Pros
-Much of the same as HEI, but higher chance of starting fires
Cons
-Again much of the same, but low damage for a HE round

HE(minengeschoss)=A weird munition used by Germany and possibly Japan. Using drawn steel like a cartridge to maximize explosive filler at the expense of steel that could produce larger fragments. Apparently very effective and used in some post-war cannons, but difficult to produce.
Pros
-Massive explosive payload for a HE round
-Potential for explosive charge to convert some of the target structure into fragments
-Fuze had delay from the start
-Explosive filler was replaced with one more capable of starting fires
Cons
-Expensive, the fuze and drawing process was not easy
-Low quality ballistics, projectile was relatively light weight for it's diameter
-Basically no armor penetration capabilities
-Smaller fragments due to thin shell wall

HE/HEI(Fuzeless)=A weird creation by a desperate Japan, in this design the fuze was omitted entirely. This allowed for more HE payload for it's size, while keeping a thick fragment producing shell wall. But it also meant the shell's ability to have a delayed explosion was stunted. Alternatively this round could have both HE and incendiary filling without compromising explosive payload
Pros
-Dirt cheap, no fuze makes it very easy to produce
-Large explosive payload for a HE round, although inferior to Minengeschoss, average payload if using incendiary as well
-Good fragment producing capabilities
Cons
-No fuze delay, damage is inherently limited as the projectile cannot pierce the skin as much as other rounds because it is fuzed by impact
-Potential safety concerns, Japan marked them with special colors to warn crews to be careful

Feel free to add any information you know of. ;D

Following this discussion thread closely with intriguing interest!

 

[ThatZenoGuy]

Contrinued!
Armor Piercing rounds

Practice/Practice Tracer= About the cheapest munition you can get, not even made out of hardened penetrator steel. Just a big ol mild steel slug designed to go through a plane or soft target, sometimes in the form of HE rounds filled with concrete/bakelite/etc instead. Can have a tracer but all tracer rounds are a bit less accurate as the composition burns off, altering it's weight.
Pros
-Super cheap
-Realistically will go through most planes
-The more fragile versions can shatter upon impact, doing MORE damage than an AP round
-Can be used as a cheap 'barrel clearing' round at the start of a belt
Cons
-Not really effective against ground targets
-No real way of starting fires on a target
-In theory could be stopped by a few historical armor layouts on a plane
-Damage isn't great, mostly punches holes in things instead of shattering parts of a plane

AP/APT= Similar to Practice rounds but designed to penetrate armor, with a hardened alloy steel core. Also an incredibly simple munition and used by just about everybody
Pros
-Punches holes in things pretty good, might even take out a lightly armored vehicle or tank in the right spot
-No plane armor can realistically stop a 20mm AP cannon round in WW2
-Pretty cheap
Cons
-Low damage, just goes straight through a plane
-No fire chance
-Could be viewed as 'excessive' against a plane target in regards to penetration

AP(c)/APT(c)= Armor piercing with a special core, usually tungsten or a special core of 'cermet' (ceramic-metal). This can pierce much more armor but is more expensive as well. Can come with an incendiary payload as well.
Pros
-Excellent penetration, no plane can withstand these rounds
-Good against ground targets
Cons
-Expensive, using rare resources
-Absolutely stupid to use on aircraft, best used on special targets
-Low damage because they can be subcaliber
-No fire chance unless incendiary payload is included

API/APIT= Imagine an armor piercing shell, except it lights on fire when it hits something, amazing! Comes in two flavors, fuzed and unfuzed. They mostly do the same thing but a fuze allows you to ignite the cartridge at the depth you want within a target, at the expensive of filler volume. Unfuzed ignites on impact.
Pros
-Sets on fire! Can set alight fuel, oil, ammunition, etc
-Cheap if unfuzed
-Still will go through most plane armor with ease
Cons
-Fuzes aren't cheap
-Fuzeless rounds can activate a bit too early, wasting the fiery burst
-Still excessive penetration against WW2 planes

APHE/APHET= It pierces armor, then explodes. If fuzed right it should penetrate shortly after penetrating a hardened steel plate. On the flipside the filler might not detonate if the target is not particularly tough
Pros
-Explodes within a target, high damage potential
-Pierces most armor on a plane
-Good against ground units
Cons
-Expensive due to fuze, hardened core, and explosive payload
-Potential to not explode unless it hits something tough, like a fuel tank, engine, heavy spar, or armor plate

All right so there's armor piercing rounds, hope you enjoy.

 

[edgeworthy]

There has been some serious work done on this.
- See https://archive.ph/KAqG

 

[ThatZenoGuy]

There has been some serious work done on this.
- See https://archive.ph/KAqG

Well just posting a link isn't exactly as engaging, now is it? XDDD And I've never been a fan of appeal to authority.

 

[PsihoKekec]

I think the unfuzed API was the most economic choice for the air combat of the WWII, the small fuzes in general were too flaky back then, API was in general stable enough not to detonate at hitting the stressed skin of the aircraft, so it was good enough for the task.

HE for strafing runs.

 

[Marduk]

AP is not a good choice, especially not for 20mm, defeating the main advantage they have over .50's, which is that 20mm can have viable HE shells capable of blowing big holes in the era's plane's thin skin and not very redundant control surfaces, crippling planes with merely few hits, which were already hard to achieve in air combat, instead of having to riddle the enemy plane with holes. If you are going to shoot AP/API only, you are better off with taking the US route of having .50 cals, with more ammo and guns at the same weight, it's not like any planes have enough armor plating to stop .50 AP spam anyway.

The famous mine shells were primarily meant as a weapon to boost the rather low amount of 20mm firepower German 109's had (not only they had few rounds per gun, their normal HE was kinda weak), and later facilitate bringing down the massive 4 engined allied bombers preferably before their .50 turrets turned the fighter into swiss cheese, and in general air to air belts on fighters were the HE heavy ones.

For strafing you absolutely want a mix of API and HE (and something along those lines was always a popular loadout for all sides, mixed belts were usually the historical answer to that question due to sheer versatility) to also be effective against armored vehicles too, and also do more serious damage against all sorts of heavily built equipment.
As later found with research on grenade launchers, a slightly larger caliber is needed for truly effective in a meaningful radius HE grenades, 25mm is about on the line, and that's with modern tech.
Well, it was kinda realized in WW2 already, if you look at the specialized attack planes that did a lot of strafing. German heavy fighter bombers and attack HS 129's had variants with high velocity 30mm, while Soviet Il-2's used high velocity 23mm with double the projectile weight of their usual 20mm mounted on fighters.

 

[ThatZenoGuy]

The Germans seemed to highly appreciate penetrative incendiary rounds against planes, I'll actually write up the incendiary post now, heheh. Although they weren't 'armor piercing' they could go through most plane surfaces with ease.

 

[ThatZenoGuy]

Incendiary Rounds

SAPI=Used by the British in WW2 in their hispano cannons. This was actually a fairly simple design, a high explosive shell body was filled with incendiary compound, and a steel 'nose cap' was screwed in instead of a fuze. This design penetrated thin armor plates, and the shock of impact on a heavier part of the plane (spars, armor, fuel tanks) activated the incendiary.
Pros
-Cheap, it's using pre-made parts which simplify logistics too
-High incendiary payload
-Activates after piercing skin
Cons
-In theory can overpenetrate
-Won't go through heavier aircraft armor
-Doesn't explode, simply sprays fire everywhere

I/IT=Not really popular in militaries, primarily used by Germany. Tracers heavily limited the incendiary payload, although non-tracer versions also existed. Used a fuze that was set on impact.
Pros
-Won't overpenetrate
-Fuzes exist in several forms, to activate on specific types of target
-Should be able to get to the fuel tanks unless they are armor plated
Cons
-Payload might activate a little too early
-Doesn't explode
-Less penetration than SAPI

I(minengeschoss)=Only used by Germany, these were similar to explosive minengeschoss rounds, but with a thicker shell-wall and fuze designed to activate inside fuel tanks (possibly hydrostatic fuze?) and when striking hard parts of a plane like engines or armor. Colossal payload for it's type, arrived late in the war. (1944)
Pros
-Largest incendiary payload
-Activates only on things you want to melt/set on fire
-Enough integrity to survive penetrating aircraft skin
Cons
-Expensive, like the minengeschoss HE rounds
-Cannot pierce armor
-Still doesn't explode, but the sheer quantity of incendiary makes up for it a bit

And there we have it, basically every WW2 shell type that I am aware of, at least in the 20mm category.