War thunder now use DeMarre formula to calculate full caliber rounds’ penetrations. But DeMarre formula needs a reference shell as reference. The reference shell should be the same shell type as the one needs to calculate (Such as calculating the penetration of an APCBC shell, the reference shell should also be APCBC). Now, calculating American APBCs normally use standard pointed tip APBC as reference shell. But due to special structure and mechanism of some , especially late WW2 and post-war American APBCs, using standard pointed tip APBC as reference shell is not historical.
To beat high obliquity caliber thickness HRA plate, especially the frontal armor of Germany tank “Panther”, U.S. army developed 90mm T33, which modified 90mm M77 with an reheat-treated harden tip. T33 was the most effective shot for the defeat of high angled target at that time (Fig 1); (Fig 2, the shell hardness comparison between T33 and T50).
This is because the harden tip of T33 will rupture while hitting high obliquity target, which turns T33 into a blunt-tip shell, reduce ricochet possibility. (Fig 3)
Similar mechanism was used in many late WW2 and post-war American APBCs, including 76mm M339, 90mm T44, 105mm T182, 120mm M358. Those shell performance like pointed tip APBC at low angel while at high angle more likely a blunt-tip shell like BR471B. We could find this in the penetration chart of T33. (Fig 4)
T33 could penetrate 3in RHA with 60° at 2200 yards, 65° at 625 yards, while T33 in game could only penetrate 67mm RHA with 60° at 10m, 100% ricochet at 65°. The error is so large that can’t be ignored. American APBCs need a special reference shell for DeMarre formula to calculate their penetration rather than using standard pointed tip APBC model.
Fig 1: Armor-piercing ammunition for gun, 90mm, M3
Fig3: Solid steel ap projectiles. conventional, truncated and tipped truncated ogival types
Fig4: Comparative effectiveness of armor-defeating ammunition
Even Gaijin themselves clarified that the Formula was to be a general solution, but that it could require some manual fine tuning in some cases- this is one of those cases.
Yeah, even if the penetration isn’t an exact match to real life (like 76 mm M1 penning ~20 mm more than RL), it wouldn’t be a big deal if T33 and other American AP rounds slighty under or overperformed, but not being able to pen a Panther’s UFP from point blank (T33) while it could from 1.2 km is a serious discrepancy which needs immediate fixing.
The trouble for making an exception from their previously hard-and-fast rule to only use de Marre (with only one reference shell used for ALL AP and APHE) for one specific shell should be obvious… it’s an exception, and it opens the door to so many more exceptions they could make… poorly manufactured Russian tank or Italian naval shells should be an exception, as one example in the other direction many have called for. Many have said using the same reference shell from 12 mm to 400mm doesn’t actually work mathematically, either. Then you have the various shell shapes, with flat noses, caps, screens, and how they should all have different individual referentials to match historical data. They’d probably feel they’d have to make all those exceptions too.
I mean, good luck, but you’re basically asking them to enter a world of hurt of exceptions and counter-exceptions that they may just feel would only lead to madness. But hey, we’ve voted down any APHE changes and they’ve said they’re not going to change APCR again either, so at least it gives players something new to argue about again.
