Russian APCR Against Face-Hardened Armor

[rexford]

When Russian AP hits the face-hardened armor on PzKpfw III and IV, the thin face-hardened layer is usually harder than the projectile nose. 51 to 60 Rockwell C hardness for face-hardened armor layer, about 52 average Rockwell C for Russian AP.

Theory with face-hardened armor is that the layer is harder than the projectile, causing the nose of the round to crack, fracture or shatter and thereby absorb energy that otherwise would go into the destruction of the armor.

With Russian APCR, projectile nose is 67 Rockwell C, which will be harder than the face-hardened armor layer. The tungsten hardness may change the equation so that the projectile gains the upper hand, but info to support such a theory is rare.

The John Salt site offers a ton of penetration stats for 17 pdr APDS, and only one is associated with face-hardened armor. Hogg, in his 1997 "Tank Killers", presents a figure of 231mm penetration at 1000 yards and 30 degrees slope for 17 pdr APDS against face-hardened armor.

Against homogeneous armor, the 17 pdr APDS is credited with 188mm at 30 degrees.

Assuming a 30 degree slope effect of 1.24 for 17 pdr APDS yields a vertical penetration ratio at 1000 yards of 286mm face-hardened/232mm homogeneous, for 1.23. So 17 pdr APDS might penetrate 23% more face-hardened armor at 1000 yards than homogeneous.

It seems realistic to assume tungsten does better against face-hardened than homogeneous. One case does not prove anything to the degree we would like.

But then again, we don't know if the Russian penetration figures put forth for their APCR are against homogeneous armor, high hardness homogeneous or face-hardened armor (an issue that Miles Krogfus may address in his upcoming AFV News article).

Giving tungsten core rounds a boost against face-hardened armor would help against PzKpfw IIIH and PzKpfw IVG,H and J frontal armor. But is that boost already in the stats?

[flamingknives]

I'd just like to pick up on a small point I gleaned from a 1915 book on naval gunnery*, regarding the basic principles of armour penetration, which is relevant here.

There are two methods of the shell passing through the armour plate of the target:

1)Piercing; the point of the shell pierces the armour and proceeds to penetrate the plate using the wedge effect.

2)Punching; the armour, being harder than the tip of the shell, breaks this off, so that the shell cannot use the wedge effect to penetrate the plate. Instead, the shell acts as a flat ended punch, which requires much more energy to defeat a similarly thick layer.

The above is my summarising of the chapter in question, and probably does not use the right terms, but I hope it gets the point across.

In effect, the strength of a sufficiently hard surface is that it forces the shell to use a less efficient method to pass though the plate.

It is also interesting to note that a softer material over the surface of the hardened plate will have the effect of supporting the tip of the shell, meaning that it can defeat a thicker plate than it would otherwise have done.

*I can't remember the reference of this, but it was written by the cheif gunnery officer aboard one of the Royal Navy's battleships. A note in the book indicated that he had been killed in action in the Dardenelles and recieved some sort of decoration (posthumous, naturally) for his conduct, but names escape me.