Not exactly shattering but break up. One needs to be aware of the fact that projectiles have two curves of penetration. One for intact penetration (german "heil"), and one for broken penetration (german "grenz"). Originally, there was was a "Durchschlag" curve, which did not specify, whether or not the projectile is intact.L/24Stug wrote: ↑27 Apr 2019 19:21K. Gr. Patr. rot Pz penetration is the same between 100 and 1000 meters @ 685 m/s m.v.
You know, it is an indication of proyectile deformation-shattering.
But what does it really means? German proyectile tests required intact penetration, ready to burst beyond the plate. Does it means it is possible that it indeed penetrated thicker plates but not in bursting condition?
For high quality projectiles, such as the Pzgr.39, these two curves fall together over a very wide range of velocity and T/D ratios. For lower quality projectiles, there is a delta between both over a certain range. Sometimes, there is only a change from one mode to another.
When an inferior projectile increases velocity past the velocity of break up for a given T/D ratio, hardness and oblicquity, the projectile experiences enough deformation to not remain in effective bursting condition anymore (f.e. ww2 soviet AP projectiles, very generally). It will break up, or worse, shatter.
However, if You have a sufficiently capped AP and increase the velocity further, the projectile may overmatch the plate by virtue of excess velocity, that is the time domain, under which the excess force is able to "work up" the projectile is sufficiently short as to allow the projectile with only minimal damage to pass once the time domain is shortened enough to prevent full damage. However, this is only possible, if the projectile can avoid shatter. Shatter will rapidly fragment the projectile in a large number of small fragments, sometimes with the lower body relatively intact if shatter is confined to nose and shoulder, only. If the projectile can prevent shatter (having a cap helps here, but the body need to be heat treated to a sweet spot in hardness, too) and only suffers break up, it can penetrate if the velocity is increased further. But it would be inefficient and requires large increases of velocity. This is called the high penetration velocity sometimes. I am pretty sure, the K.Gr. rot Pz. is actually showing this effect due to the minimal increase in penetration over shortened range.
However, this effect is confined to a certain range of T/D ratio´s. It´s not infinite. So it is correct to perceive the maximum T/D ratio for a given projectile it can perforate at any velocity. Past that critical T/D ratio, increases in penetration will only break up the projectile further, actually lowering the penetration. For the 75mm K.Gr. rot Pz, this critical velocity was 700m/s (only good quality lots), for the 75mm Pzgr.39, this critical velocity was 1240m/s (again, only good quality lots), both at 30° and against 95 or 85 kg/mm^2 tensile strength plate.