Overhaul of Gaijin calculator

Do you support changing the AP calculator?
  • Yes
  • Yes, with BR changes
  • No, with comments

0 voters

I started this suggestion on the old forum but that is no longer available, so I’m restarting it here.

This initially started as something for uncapped, solid AP but I believe it can be used for APCHE and APCR. I’m still working on Soviet APHE.

I’ll start with solid, uncapped AP again and more or less copy what I posted on the old forums.

My suggestion is to modify the current armor penetration calculator to better represent AP performance. With the adoption of the formula system, the performance of AP and APC rounds were made uniform, disregarding historical documentation. While this has reduced the work to implement new rounds and eliminated debates about penetration standards. The downside is specific round performance is no longer historical. The issue is further compounded by the use of standard slope modifiers. The slope modifiers come from WWII Ballistics, Armor and Gunnery. They are dependent on the penetration data from the same source. The issue starts with how Gaijin implemented its formula. Instead of calculating the necessary theoretical penetration for the standard WWII BAG slope modifiers to work, Gaijin attempted to account for certain AP rounds shattering. The “shattered” vertical penetration is reduced from the theoretical penetration of the round. When that reduced vertical penetration is applied to the standard slope modifiers, the sloped performance of the round is also reduced. In many cases, the shattered vertical penetration performance is accurate, but the reduced sloped penetration is not. In other cases, the round did not shatter against vertical armor, so both its vertical and sloped penetration is incorrect. This issue can be addressed by removing the “shattering” modifier from the AP round version of the calculator and changing the K factor to 1800.

Based on work I have done for previous reports, I have been able to establish a few key factors in the AP formula. First, the formula uses a K factor of 1900. Second, the uncapped AP formula applies an additional .9x modifier to the result. That .9x modifier is to represent the shot shattering.

Here’s a screenshot of the formula results. First is the AP results, then the same round with the APCBC box check. AP is 175.20, APCBC is 194.67. 175.20/194.67 is .8999 or rounded up to .9.

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Here is a screenshot of a Demarre calculator with the K factor set to 1900. In this version, the “a” variable is the K factor. As you can see, the standard result is 194.67, which is the APC result. The AP result is 175.20. Both results match the calculator results from Gaijin.

Spoiler

IMG_6344

Next, we need to establish a basis for the 1800 K factor. I’ll use 90mm T33, since its a well documented round. The 90mm T33 will defeat the 80mm Panther glacis plate to roughly 1400 yards. This is shown by the following document. The penetration chart below shows the 90mm T33 will pen the 3.15" (80mm) at 55 degree glacis plate to about 2425 feet per second. The chart is based on US navy criterion, so the standard is pretty strict. Its a good basis for the performance of the round.

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Using the in game armor protection analysis, we can see the Panther glacis equates to 171mm of protection against the 90mm T33.

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Using the Demarre formula to change the penetration at 2425 fps to the muzzle velocity of 2800 fps, we get the following penetration.

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Now, going back to our Demarre calculator, with the K factor set to 1800, we get the following results for 90mm T33 at 2800 fps.

Spoiler

IMG_6346

To verify the results, we can look at another round. 57mm M70 AP is not prone to shattering, so we can use it as a good reference. The navy criterion chart is below.

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At its muzzle velocity, the M70 AP penetrates a little over 5.5" or 140mm of vertical armor. Using the 1800 K factor, we get the following result.

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Roughly 142mm instead of over 140mm is close enough to call it good.

So, basically, I suggest removing the .9x modifier for uncapped solid AP and changing the K factor to 1800.

15 Likes

Ahh my god, this is completely necessary, the penetration calculator is one of the three biggest bugs that the game has had for years, and it would be about time they fixed at least this problem with the hope that they fix the others. In favor completely.
It would only be necessary to modify the penetration calculator of the other projectiles, for example, since the 3bm8 of 100 has practically the same penetration as the 3bm25.

5 Likes

For APCR, we can use the same DeMarre formula as AP. Using a calculator meant for tungsten carbide cores, I established a few values and then adjusted the DeMarre formula to match.

For example, 76mm M93 uses a 3.95 pound, 1.5” diameter core. At a velocity of 3400 fps, it will penetrate 238mm. 90mm M304 uses a 8 pound, 1.895” diameter core. At a velocity of 3350 fps, it will penetrate 300mm. Soviet 85mm BR-365P uses a 1.408 pound, 1.082” diameter core. At a velocity of 3444 fps, it will penetrate 166mm.

To adjust the formula, I used the core diameter and weight with a K factor of 1800, with a weight multiplier of 1.37x. That resulted in the M93 at 241mm, the M304 at 304mm and the BR-365P at 167mm.

5 Likes

With APC, we can use the 1800 k factor and a .9x weight modifier to represent the cap that is lost during penetration. To represent the HE filler, a 5x modifier is applied to the HE weight and subtracted from the weight total. This brings it in line with the current APC values used by Gaijin.

120mm T14E1 is a solid APC fired by the T34 heavy tank. The current calculator gives a result of 283mm. My suggested changes give a result of 284mm.

90mm M82 is HE filled APC fired by various tanks in game. One variant has a velocity of 2670 fps. The current calculator gives a result of 173mm. My suggested changes give a result of 173mm.

The results are fairly consistent, even with large filler variants some tanks have.

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Using ballistics date I’ve found for US projectiles, I made some representative charts out to 2000 yards. This one is for the M1 76mm gun and M7 3” gun.

IMG_7127

2 Likes

I really hope this is implemented, WW2 shell calculations are one of the more noticeable places in WT that seem entirely biased towards RU and this would help resolve that.

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The calculator system is salvageable but it is limited. I hope they make these changes because it would really balance a lot of things out.

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For Soviet APHE and APHEBC, the setup is similar to APC but a .7x modifier is applied to the total round weight instead of a .9x.

Here is a chart for the ZIS-S-53 on the T44.
IMG_7128

3 Likes

I’m curious about the Soviet 100 and 122mm ammunition, because they seem a bit strange to me, firstly the 122 sharp and the flat have the same penetration at 0° when the sharpened ammunition should have a bit more penetration at 0°, and then there is the APCR of the 100mm cannon that drills less than the APCBC.

Gaijin doesn’t differentiate between the sharp and blunt AP designs when calculating penetration. For the 122mm, I believe the AP and APBC have the same HE filler, so their penetration comes out the same. From that point, the only difference is their ballistics. The APBC maintains its velocity better, so it loses less pen over distance.

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But it would actually affect penetration, right? For example, there is also the M82 90mm ammunition whose nose is much more rounded than the M77 and the T33. Apart from that it would also depend on the strength of the nose, right?

It should affect penetration. Sharp nose and blunt nose rounds use different mechanisms to penetrate armor. The issue is Soviet metallurgy was so poor, the sharp nose rounds were not very effective. The blunt nose was meant to reduce shattering.

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Here’s some data I’ve seen on the Soviet 100mm. The BR-412B is over performing by quite a bit.

Protection limit considers a penetration to be when the round produces spalling on the inside of the plate. Even at that low level of standard, the BR-412B was only rated at 7.01” or 178mm. And that was using cast armor.

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On one hand the graph says it is overperforming against flat armor.
On the other the graph also says it would go through over 100 mm of cast armor at 60º (granted, protection limit, according to your comment).

I’ve seen a simulation that explains this better. Russian rounds had poor metallurgy as you said which caused them to shatter. It seems that this same shattering also made it so they performed better against angled armor, much like T33 APBC. It seems that their real life performance against angled armor came from the shattering characteristics of the round rather than the blunt nose itself.

Yeah, the Soviet blunt AP should more or less match pointed AP against sloped armor but I think it was better against under matching armor. I’m not entirely sure.

Just for reference, the T43 (T33 from the long 90mm) would pen 280 BHN 4” cast armor at 60 degrees at 3007 fps. That’s using army standard, not protection.

With some help, I gathered a bit of information about German APCR. Using my suggested changes, here’s how a few of them would look.

PzGr 40/43: 2.0 kg 36mm core at 1130 m/s is 313mm.
8.8cm PzGr40: 2.0 kg 36mm core at 930 m/s is 237mm
PzGr 40/42: 1.12 kg 30mm core at 1130 m/s is 252mm
7.5 cm PzGr 40: .90 kg 28mm core at 990 m/s is 192mm.
5 cm PzG4 40: .34 kg 21mm core at 1180 m/s is 169mm

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I’ve made some updates to my changes. The APCR modifier was changed from 1.25x to 1.37x.

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Comparing my results to some posted by Peasant in another thread shows the AP and APCR results are reasonable for Soviet style as well. The APC is known to overestimate many APC rounds but I don’t know of a reliable way to account for various cap sizes. It would have to be done on a round by round basis.

IMG_7128

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Here are a few 90mm tables.

90mm M3 Early

90mm M3 Late

90mm T15

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100mm D-10T chart. Replaced BR-412P with 3BM-8 APDS, based on limited info I could find.

1 Like