There is a a lot wrong with the Guns and ammo.
One after the other.
First the ammo in general:
First the AP round:
Pzgr. L`Spur. o.Zerl. (Ph.) (ApI-T) 0,148kg 830m/s 40mm/10m (Click to show)
(In game implemented with 800m/s and 37mm/10m)
Note: Used against ground targets. Soft and armored. 3g White Phosphor Core.
Were fully replaced by the empty ones and later .Zerl in the Desert and other hot places, as the Phostphor had a nasty tendicy to self ignite in hot weather.
The Ph. marked ones were standart with the filler, however they also existed with an O. which indicated they didnt have a filler and were only 143g (and 835-840m/s).
(Velocity for L/55 is 800, 805-810 for the 143g.)
And the HEFI-T round:
Sprgr. L`Spur. m.Zerl. (Hefi-T Sd.) 0,120kg 900m/s 6,2g Pent (10,54g) 5mm/10m
The AP round is ok, and the main way to use (if available), would be nice to have Pzgr.40 in game, but whatever.
Against Infantry that is. Because unlike all the other AT Rifles, against modules and ammo (even tho also beeing Incendary ammo), it does quite few damage against them, requiring multiple shots to destroy such. While also the russian 20mm and Japanese 20mm can one hit modules such as engines and transmissions.
However overall the HEFI-T (which most likely is copied from WT, and by that also wrong then, with only 115g (instead of 120g), 6g Pent (Instead of 6,2g Pent (or 6,6 H.5 of the actual HEFI-T round))
But overall is really BAD because the filler and shrapnell are so few, that against Infantry it needs direct hits to damage, however even on DIRECT Hits against infantry, you need 3-4 rounds to kill, while the AP can one shot Infantry, as it should, its a 20mm round after all, and the 120g 20mm HEFI-T round at 900m/s should most definitly absolutly shred infantry on hit. And it has also pretty much no penetration (while IRL also around 1 cm, effective against gunshields).
So that out of the way, that the HE round is incorrect and lacks damage, as well as the AP round lacking damage against Modules. The He rounds effectively half the available ammo amount of effective ammo of the Pz II Ausf.C, as they are really bad, and require the full depleation of the magazin to change ammo type.
There is more:
The stationary AA gun doesnt get the AP round, prossibly duo to ballancing, however only gets 3x 20 rounds Mags overall, which is quite a low amount, and should perhaps be doubled to 6x Magazins.
The Pz II Ausf.C also recives the 20 round mags, while IRL it only got the 10 round magazins, its doubtfull that the long 20 round mags even fit inbetween the gun and turret wall.
There is also other HE ammo, Tracerless higher capacity. Mainly 2 variants, same shell different filler:
Sprgr. Erd. o.L'Spur. o.Zerl. (He) 0,120kg 900m/s 11g Pent (18,7g)
Note: Only against groundtargets. Other name is Spr.Gr.39.
(Couldnt find the correct drawing, the Br.Sprgr. o.L’Spur is basically the same, just different filler with Zink.)
And the AA variant, with Incendary addition:
Brsprgr. o.L'Spur. m.Zerl. (Hef-I Sd.) 0,120kg 900m/s 20g H.5 and Zink
Note: Against ground and air targets. No tracer at all to have a fully capacity He (H.5) and Incendary (Zink) mix. (Weight calculated by Killakiwi 7g H.5 13g Zink)
So in summary i suggest:
Ap ammo: Increase the Damage against Modules. Maybe Add Pzgr.40 (In comparison the Russian 20mm T-60 and Japanese Ta-Se both can destroy Modules in 1 hit.)
He ammo: Increase direct hit damage (to one hit, instead of 3-4 hits) against infantry. Fix it overall, 120g and 6,2 g Pent or 6,6 g H.5
Maybe replace it with the Sprgr. Erd/39 or Br.Sprgr. o.L’Spur
Give the AA guns more Ammo.
Change the Pz II Ausf.C magazin to 10 rounds.