How to calculate shaped-charge damage for theoretical explosives?

[Rupert]

Originally Posted by Sam Baughn

High-Tech gives standard TL7 40mm grenade launcher shells (I think that's the right terminology) 4d of damage. This seems to be consistent with 32g of Composition-B filler, which seems to have been standard for 1970s shells.
At TL8 that goes up to 6d+2, which is about 163% of the TL7 damage, which implies the TNT-equivalent of explosive in the shell is 264% of what is in the TL7 one. I can't find a source for what filler is used in modern shells, but some internet research suggests that the explosive used isn't much more powerful, probably just having more RDX in the mix, giving it about 10% better REF. That means the main difference must be packing more explosive into the shell. RDX is a bit denser than TNT, so replacing most of the TNT with RDX would help somewhat, but not nearly enough. I guess the difference is a thinner casing and smaller fuse, allowing a bit more material to be jammed in.

A much smaller fuse is the big advance here.

Looking at shaped-charge warheads, things seem more complicated.
The TL7 HEDP shell does 4d(10) with its jet, and 4d+2 explosive. That implies a bit more explosive filler than the HE shell, around 27% more TNT-equivalent, so likely something like 40g of Composition-B.
The TL8 HEDP does 6d explosive, so probably around 78% more TNT-equivalent. Like the HE shell, this seems to be mostly a case of packing more explosive into it than significant improvements in REF.
The jet damage goes up to 7d(10), or 75% more than the TL7 one. That looks a lot like the jet's penetration goes up in a linear fashion with the force of the explosion.

HEAT shells improve not just in the power of the explosive, but in the shape of the hollow cone, and also in the composition of the liner.

However, the TL9 shaped charge warheads in Ultra-Tech make a massive jump in effectiveness, with the 40mm one doing 6d×4(10) with 4d explosive. The relatively low explosive damage implies that this isn't a super-high REF explosive, but I find it hard to believe that other factors could account for more than triple the penetration, even if you use uranium or something as the liner material.

The low explosive damage can also mean that more energy is being pushed into the penetrator jet, leaving less to cause the omnidirectional explosion.

So, it seems that the shaped charge damage in Ultra-Tech is way off and the HE / HEC damage might be a bit low. Adjusting normal explosive effects (e.g. HE damage) to account for different effectiveness in future explosives seems fairly straightforward; just figure out the REF and weight of explosive, then multiply them together and use the usual explosion rules.
But for shaped charges, I have no idea what appropriate values are. My instinct is to make them scale at the same rate as normal explosives, i.e. at the square root of mass × REF, but since I'm not a mathematician, scientist, or engineer, I don't think my instincts are to be trusted on this.

Can anyone who actually knows what they are talking about comment?

Assuming the same tech, form factor, materials, etc., my recollection is that HEAT penetration is proportional to the diameter of the warhead (and thus the cube root of mass). However given the complex interaction of explosive, liner, geometry, etc. that does not mean it scales with the cube root of explosive energy in any other situation.

One thing to be aware of is that UT's 40mm shaped-charge grenade stats were taken from real life, and HEAT warheads that small tend to be terrible. There just isn't room for good geometry, and a fuse, and a good stand-off distance, and a decent amount of explosive. They also try to be HEDP, and that costs weight and volume for fragmentation layers and/or enhanced blast.