CMBB Slope Effects vs T34 Armor

[rexford]

JasonC brought up a very good question on the George Forty thread, why do the published slope effects for German 75L43 APCBC look so much lower than what was found during U.S. firing trials with 75mm ammo. A very good question that took me awhile to figure out.

CMBB presents penetration stats vs typical enemy armor, and Russian plate used two distinct hardness levels during 1943, very high hardness for 65mm and below, and medium hardness for above 65mm.

When 75mm APCBC hits high hardness plate the plate will lose resistance relative to medium hardness plate.

So here's the scoop for 75L43 APCBC penetration stats presented in CMBB (based on my examination of the numbers):

The 0 degree penetration stats are against medium hardness plate, the 60 degree figures are against high hardness.

75L43 APCBC Penetration Data

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100m

128mm at 0 degrees in CMBB (medium hardness)

58mm at 60 degrees in CMBB (high hardness)

47mm at 60 degrees with slope effect from U.S. firing trials (medium hardness)

So CMBB is saying 58mm of high hardness armor = 47mm of medium hardness when it's hit by 75mmL43, so the high hardness plate is 81% as resistant as medium hardness.

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500m

117mm at 0 degrees in CMBB (medium hardness)

55mm at 60 degrees in CMBB (high hardness)

44mm at 60 degrees with slope effects from U.S. firing trials (medium hardness)

So CMBB is saying 55mm of high hardness armor = 44mm of medium hardness when it's hit by 75mmL43, so the high hardness plate is 80% as resistant as medium hardness.

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1000m

104mm at 0 degrees in CMBB (medium hardness)

51mm at 60 degrees in CMBB (high hardness)

40mm at 60 degrees with slope effects from U.S. firing trials (medium hardness)

So CMBB is saying 51mm of high hardness armor = 40mm of medium hardness when it's hit by 75mmL43, so the high hardness plate is 78% as resistant as medium hardness.

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2000m

82mm at 0 degrees in CMBB (medium hardness)

43mm at 60 degrees in CMBB (high hardness)

33mm at 60 degrees with slope effects from U.S. firing trials (medium hardness)

So CMBB is saying 43mm of high hardness armor = 33mm of medium hardness when it's hit by 75mmL43, so the high hardness plate is 77% as resistant as medium hardness.

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Our calculations indicate that 45mm plate at 60 degrees should resist 75L43 APCBC with 76% of the resistance of medium hardness armor, so CMBB is in line with our equations.

[rexford]

I lined up five elite PzKpfw IVG's against seven conscript T34 M43 in a June 1942 scenario. Range between tank lines is 1600m, no tungsten ammo.

Every 75L43 hit on the T34 front upper hull penetrated or gained a partial penetration.

Considering that the 75L43 APCBC penetrates 46mm of 60 degree high hardness armor at 1600m, and the armor quality is 90% (so 75L43 penetrates 51mm at 60 degrees), one would expect few harmless bouncers at 1600m even with a slight angle.

By the way, I still find the 45mm at 53 degree front lower hull armor on T34 to be very questionable. In a 2100m scenario, PzKpfw IVG hits on the T34 front lower hull penetrated in every case (May 1942 scenario, no tungsten ammo).

All T34 drawings measure a 60 degree angle on the front lower hull, many sources say 60 degrees. Only a possibly mislabeled drawing on the Russian Battlefield web site has 53 degrees.

[K_Tiger]

To hit the lower hull at a distance from 1600 meters and more, you can call yourself a "lucky" one....

[rexford]

Originally posted by K_Tiger:

To hit the lower hull at a distance from 1600 meters and more, you can call yourself a "lucky" one....

Yes.

But three T34 were knocked out in one turn with 2100m penetrations of the lower front hull by PzKpfw IVG without tungsten. So it can and does happen. And shouldn't have happened.

[K_Tiger]

Do we play the same game? three hits in 2100 meters? not to mention the area....

Yesterday, one of my panthers missed a sherman three times in the range from around 400 meters and it was a crack crew.

[Bruceov]

Why is high hardfness plate less resistant than medium hardness plate

[rexford]

Originally posted by K_Tiger:

Do we play the same game? three hits in 2100 meters? not to mention the area....

Yesterday, one of my panthers missed a sherman three times in the range from around 400 meters and it was a crack crew.

There were a horde of PzKpfw IV firing on a bunch of T34, and it seemed that all the hits landed on the front lower hull. Not your everyday happening.

[rexford]

Originally posted by Bruceov:

Why is high hardfness plate less resistant than medium hardness plate

Medium hardness plate, 220 to 300 Brinell Hardness, is designed to have good ductility so it can take hard hits without cracking. Shermans used medium hardness armor.

High hardness armor, 450 Brinell, has low impact resistance than good medium hardness plate.

A 45mm medium hardness plate will resist like 45mm of medium hardness armor against 20mm and 90mm hits. A 45mm high hardness plate may resist 20mm hits like 53mm of medium hardness plate, but will resist 75mm hits like about 34mm medium hardness because it cannot take the impact with cracking.

Russian tankers talk alot about how ricochets off the T34 could result in armor flakes flying off the armor interior, injuring or killing the crew. It's due to the brittle nature of the plate.

Russian tankers who fought in Shermans noted that ricochets did not result in internal armor flaking, like the T34, because the plate was medium hardness and had high impact resistance.

High hardness armor is like auto glass, it works really well against small objects but can't take large hits very well and when it is penetrated it can send shards flying off into the driver compartment.

The good thing about high hardness armor is that it can be quicker to make than medium hardness armor, because one doesn't have to spend as much time reducing the hardness to a specific range and getting the correct temper that will assure high impact resistance. So high hardness armor may have allowed more T34 to be made, although they were not especially resistant to PzKpfw IV and StuG III 75mm hits.

Prior to October 1943, the Americans made quite a bit of medium hardness cast armor that was very brittle due to the composition and heat treatment.

German face-hardened armor uses a thin 500 to 600 Brinell hardness surface layer to break up the nose of projectiles, but the bulk of the armor thickness is around 350 Brinell Hardness area and provides good impact resistance.

Face-hardened and high hardness armor is good when you have thin plates under attack by small rounds, and you wish to boost the resistance. Like an armored car or halftrack attacked by rifle or machine gun bullets. U-Boats supposedly had face-hardened conning tower walls to boost the resistance to 20mm aircraft cannon fire.

The Russians noted during the Spanish Civil War that penetrations of the German tanks with high hardness Krupp armor usually resulted in severe crew casualties as the armor shattered and allowed pieces to fly inside the tank. Russian T26 tanks used medium hardness armor and unless a round directly hit a crew man it was common to suffer penetration without crew injury.

[ November 28, 2003, 04:33 PM: Message edited by: rexford ]