We gonna do this?
Ok, let’s start:
Yes. They’re called SLAP rounds, and they were first used in combat in the Gulf War in 1990. .50s from the time period and BR range we’re talking about did not (note: tungsten <> “tungsten steel”)
Yes, the little tungsten they had was saved up to give some APCR to 37 and 50 mm guns (the 5-15 rounds you mention). That’s why 20mm APCR production dried up after the initial allotment of 90 rounds per gun in early 1941, which was all exhausted by early 1943. It was never given to non-tankbuster aircraft and rarely if ever to AA weapons to save as much as possible for the light tanks, so those vehicles should likely not have it in quantity in game, if we’re being purely historical. As I said, I would make an exception for the Horten 30mm because the only way you end up with a lot of Hortens is an imaginary world where Germany also has a lot of tungsten, so it’s imaginary all the way down anyway.
Funny, I remember being VERY precise of the order of tracer and other “special” rounds when I loaded my magazines and MG belts in the military. And clearly in WT you “mix belts”, on nearly every single belt fed gun in game, so I really don’t know what game you’re playing. I’m quite confident if I was commanding a Pz II and was down to my last couple APCR rounds in 1943 I’d have mixed them in even if I didn’t have a full mag.
Ok, you want “in line with history”?
The Horten would likely have been armed with the MK 108 cannon, in 30x90RB caliber. APCR was NEVER produced for this weapon, historically, muzzle velocity of the shorter cartridge was too low for it. (The use of MK 103s by the game version of the Horten is itself quite ahistorical).
APCR ammo WAS produced for the MK 103, in 30x184B caliber, the much higher-powered weapon of the Hs 129B, Do 335 and the FlakPz IV. You are right that those weapons’ users were told not to waste their APCR shooting at aircraft. Because you’re basically destroying your country’s war factories, machine tool by machine tool you just frittered away, with every round, when you wasted tungsten that way.
Like I said, the Horten is imaginary so give it whatever. But HVAP instead of AP in those German 20mm AA platforms (in a mixed belt! I thought you said they couldn’t do that!) is dumb and ahistorical, and giving those mixed belts instead of pure HVAP ones to post-1940 20mm light tanks and the like would give a more realistic take on what the Wehrmacht’s real world capabilities against the French and British and Russian armor they would have faced would have been.