Just to be on the safe side, I’ve collected some data from ammunition collectors on the exact average diameter of the core for 90mm HVAP round, to be sure the value found in the Swiss doc is not a fluke.
“Just picked up this tungsten core today. Weight is 8.0 lbs (3.636 KG), it is 6.7” (170.8mm) long and is 1.892" (48.05mm) in diameter. The info on the base is pictured."
"Weight 3.6kg, diameter 48mm, total length 167mm, length of cylindrical part 123mm, density about 15 point something, so probably tungsten carbide. "
“…my best guess is its the core from one of these 90mm rounds.
The core on mine is 48mm wide, 170mm long and weighs 3637g.”
“This object is 6.75 inches long, 47.8 mm in diameter and, get this, weighs 8 pounds! It is one of the heaviest objects for its size that I have ever lifted.”
“the core is 170mm long and 47.8mm diameter.
It weighs 3642g”
However, notice the difference in the definition for a complete penetration
Good lord that’s a lot of variability between cores… Granted a military archive document is more likely to work with the devs as what is intended for the rounds production, than from random production and metal density variances.
I’ve observed that ballistic limits obtained using Protection criteria are not analogous to either Army or Navy limits.
If the back of the armour is ductile enough, no spalling will occur with incomplete penetrations, and the aluminum sheet will be perforated only by projectile itself passing through the armor, in which case the ballistic limit is identical to Navy limit.
Alternatively, if the armor ejects spall as soon as cracks appear, the Protection limit matches the Army limit.
But, on average, it’s somewhere between these two extremes.
I’m saying it’s very likely a mix of both, due to the nature of tungsten carbide braking apart or shattering during penetration. From what I remember seeing of the Soviet document, their criteria for apcr is very similar.
Applying existing models of subcaliber shells penetration to the soviet “heavy carrier” APCR will be a challenge.
Spoiler
The soviets seem to have obtained ballistic limit against a single plate thickness and extrapolated that using DeMarre equation. Which is technically “historically accurate”, but I dont believe DeMarre equation will produce accurate predictions when applied to these unusual shell designs.
For very thin plates the penetration process concludes before the carrier hits the plate and separates from the core. The projectile has ballistic limit equal to that of a 3kg 28mm diameter core.
On the other hand, as the plate thickness becomes much bigger, the initial contribution of energy from the carrier to the core becomes smaller and its penetration asymptotically approaches that of a conventional APCR that has penetrator mass equal only to that of the core.
Its because the base of most APCR/HVAP carriers is not robust enough to survive the impact. The base of the core will just punch through it and the rest of the carrier will slide off around it and splat on the armour without transferring any appreciable amount of energy to the core.
Not necessarily true with the German HVAP types. With those, the Nose cap is usually bakelite or plastic, and the rear part of the carrier is steel.
In fact, the 75mm Pzgr40, and 76.2mm(R) Pzgr40 have an interesting carrier design. So they may behave differently than the later 88mm and 75mm 40/42 designs.
Diagrams
It’s also possible, that T30E16(M304) and its derivatives benefit from having the steel base cap, which may contribute an unknown amount of mass/force to the core during initial penetration. The steel base cap on those rounds weighs about 2.1kg. For example, using the 2C6 Calculator, for M304 to reach its historic 12.4in (314.9mm) at muzzle velocity, the steel base cap would need to add 310g to the mass of the core during initial penetration. That’s going by the natural hardness curve, without normalizing to 220bhn.
I think it’s not a matter of it being steel or not, but simply that the Russian carriers are a lot bigger and as such the core can’t punch through the base of the carrier.
You can somewhat see it in this simulation of M93 against the Ferdinand’s upper plate.
However, even in this case it isn’t very pronounced, only noticeable when the core is already about halfway into the plate of armor, really. It definitely doesn’t look the same as what @Peasant_wb illustrated.
On a side note, since APDS is also part of this topic, I have a few things to share.
For some reason, Gaijin has decided to not actually use the diameter of the core for their penetration calculation.
APDS rounds have 3 diameters, those being the bore diameter, projectile diameter, and core diameter. Together with this there’s 2 relevant weights for the game, those being projectile and core weight.
The way that Gaijin has done their calculator is that the core diameter for any APDS round is the same as the projectile diameter. Here’s what I mean, using the 76 mm M331A2 APDS round.
M331A2 characteristics
The values of “mass” and “ballisticCaliber” are relevant to the projectile as a whole, while “damageMass” and “damageCaliber” are relevant to the core. From what I’ve measured, M331A2 has a roughly 38.1 mm core diameter. Core weight is also wrong, at least according to a model done by @Conraire, where the weight of the core was roughly 1.81 kg).
I do not understand why Gaijin has decided to do the calculator this way. It actually leads to weirdly different results on stuff like the Russian 100 mm 3BM-8 and 122 mm 3BM-7/11. These Russian APDS rounds all use the same exact 50 mm core, however they have different jackets, with the 100 mm 3BM-8 having a lower diameter and longer jacket, and 122 mm 3BM-7/11 having a shorter and wider jacket
Russian APDS
And this is reflected in the game, as 3BM-8 ends up with a 55 mm “ballistic” and “damageCaliber” while 3BM-7/11 ends up with 58 mm.
