Notes for Kip on Penetration Factors

[rexford]

Kip,

Was reading an article on the web that you wrote on the CM penetration stats, and thought the following might interest you.

Penetration of WW II rounds into vertical homogeneous armor is a function of the following factors:

1. Nose hardness (harder noses penetrate more, in general)

2. Nose shape (pointed noses penetrate more than flat noses)

3. HE burster size (larger bursters weaken the structure and decrease penetration)

4. Armor piercing caps (absorb energy and decrease penetration)

5. Quality (brittle structure supposedly hampered Russian 45mm early in war, U.S. 75mm AP contained irregular powder charges and had a tendency to shatter, and U.S. 76mm APCBC had a tendency to shatter fail when it should easily penetrate due to low shoulder hardness behind the nose which lead to bulging)

For WW II ammo, the average German APCBC nose hardness was highest at 63 Rockwell C, with American APCBC at 54.5 and Russian APBC at 50. German 75mm L48 APCBC penetrates about 105mm of vertical rolled homogeneous plate at 619 m/s, U.S. 75mm APCBC penetrates 91mm, due to the American round having a softer nose and a larger HE burster cavity.

Russian APBC had a flat relatively soft nose which significantly lowered vertical penetration against homogeneous armor, and the effectiveness against 30 degree sloped armor was also impacted. April 1943 Russian firing tests with 76.2mm BR-350A and BR-350B APBC against Tiger 82mm side armor resulted in no penetrations at 200m with a 0 degree impact angle, and the shots failed at 100m during September 1943 trials.

The Russians increased the nose hardness o a limited number of production 76.2mm APBC rounds and the penetration climbed by about 10%. The Russian flat nose APBC does not follow the DeMarre equation (penetration proportional to velocity raised to 1.43 power).

With regard to nose shape and caps, 17 pdr uncapped AP penetrates more than 200mm vertical plate at 2900 fps while 17 pdr APCBC penetrates less than 180mm.

While armor piercing caps decrease homogeneous armor effectiveness they boost performance against face-hardened armor and may protect rounds from shatter.

[John Kettler]

rexford,

Most interesting! Also, wanted to let you know that I got your note, for which my thanks. I shall continue to practice patience, confident that its reward will be an even tastier informational dish.

Regards,

John Kettler

[kipanderson]

Rexford, hi,

Thanks, very good of you to go to the trouble. Always good to hear from you.

Very interesting stuff, but the article you read must have been quite old as I certainly have not written one in the last year or two. Of course, truth be told, our hobby of CM is now four years old… hard to believe… so who knows what I wrote in the early years.

I still regularly turn to your great book on the subject…. Very much “the” single source authority on such matters and sure to remain so.

Hope you are well,

All the best,

Kip.

[Andreas]

Kip

He may refer to the article on Der Kessel.

[rexford]

Originally posted by Andreas:

Kip

He may refer to the article on Der Kessel.

Yup. That's the article which included some stuff on CMBB.

I recently did some graphical additional work on the high hardness modifiers, 37mm Pak AP has about 1.26 multiplier versus 45mm T34 plates (plate resists like 45mm x 1.26 of good quality medium hardness plate). The 50mm Pak 38 APC will have about a modifier of about 0.95 (45mm x 0.95), and around 1.05 against T34 65mm turret side on M42 versions (65mm x 1.05).

Spring 1942 German tests showed that 50mm Pak firing APC penetrated KV-I 75mm/30 degree driver plate between 100m and 200m, and 37mm Pak firing APCR penetrated T34 65mm/30 degree turret side at 100m (listed penetration for 37mm APCR is 64mm at 100m, so high hardness is about same as medium hardness against small tungsten core).