On a side note I’ve found a bug between the stated penetration of APCR rounds and their actual penetration.

From the math I’ve ran, I am fairly certain of the cause. Stat cards are using projectile diameter to calculate a caliber to thickness ratio, rather than using the APCR round’s core to calculate it. This leads to a higher C/T, which means a bit better slope modifiers, so the stat card ends up generally overestimating penetration.

https://community.gaijin.net/issues/p/warthunder/i/hQRlCDRp2HqS

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More detailed explanation

APCR rounds don’t overmatch, but they do undermatch. They currently have slope effect tables for C/T ratios of 0.5 and 1, meaning that if C/T falls below 0.5, it defaults to 0.5, and the opposite if it falls above 1.

For example, at 60º the slope effects are 4.5 and 4.3 for C/Ts of 0.5 and 1 respectively.

Say you’re using M304 HVAP, which in WarThunder has a core of 38.1 mm and an actual caliber of 90 mm. If you were to shoot at a 60 mm thick RHA plate at 60º, you’d end up with a C/T of 0.635 when using the core diameter, meaning that the actual slope effect would fall somewhere between 4.5 and 4.3, closer to 4.5. Doing the math, the exact slope effect would be 4.456, giving an effective armor value of 266.76, which matches the screenshot I provided in my bug report, at 267 mm.

However, stat cards don’t use the core, they use the actual projectile diameter. This would mean that against the same plate, you’d end up with a C/T of 1.5, which defaults to the value of 1. Doing this, the slope modifier that the stat card **thinks is correct** ends up at 4.3, meaning that the effectiveness of that plate would be 258 mm.

I have created a simple 60º pen calculator for APCR in Desmos graphing calculator.

APCR pen calculator | Desmos

You can set C to the caliber you want (for example, you can test all I’ve said by setting it at 38.1 mm or 90 mm).

With Y you can set a flat penetration value, and the graph will provide a 60º pen value for that specific caliber.

With X you can set an armor thickness value, and the graph will provide an equivalent protection value against that caliber.

The “line” itself is separated in 3 colors for the sake of understanding. Red is for for the C/T defaults to 1, blue is for when the C/T falls between 0.5 and 1, and green is for when C/T defaults to 0.5.

The table is there purely to reference those values rather that having to repeadedly write them. This also means that if you want to test the slope modifiers for another angle, you just need to substitute the values on the table and everything will work (for example, 30º slope modifiers are 1.35 and 1.3 for C/T of 0.5 and 1).