[3e] Statting a CTA weapon

[Varyon]

The link requires a login to access. If you can provide the caliber (looks like 45 mm) and either mass of the projectile alone and muzzle velocity, or simply muzzle energy, you can get a decent-ish estimate on GURPS damage with the equation Douglas Cole worked out, where average damage in points (divide by 3.5 to get damage in dice) is equal to 0.6*SQRT(KE/cal^0.4), with KE in J and cal in mm. I think he may have mentioned before that it wasn't quite right for cannon performance, but I may be misremembering.

[GURPS Fox]

Originally Posted by Varyon

The link requires a login to access. If you can provide the caliber (looks like 45 mm) and either mass of the projectile alone and muzzle velocity, or simply muzzle energy, you can get a decent-ish estimate on GURPS damage with the equation Douglas Cole worked out, where average damage in points (divide by 3.5 to get damage in dice) is equal to 0.6*SQRT(KE/cal^0.4), with KE in J and cal in mm. I think he may have mentioned before that it wasn't quite right for cannon performance, but I may be misremembering.

But what about the ammunition? Like how to stat the weight, cost, and volume of a CTA round?

I can do the damage figures. The problem here is the ammunition's weight, cost, and volume modifiers. For example, if I want to make a CTA gun, what modifiers are needed?

[Varyon]

Originally Posted by GURPS Fox

But what about the ammunition? Like how to stat the weight, cost, and volume of a CTA round?

I can do the damage figures. The problem here is the ammunition's weight, cost, and volume modifiers. For example, if I want to make a CTA gun, what modifiers are needed?

It looks like you have the mass and volume already, although your mass doesn't match any of the ones I can find here. The thing that looks to be unique about these rounds is their telescoping design that allows them to have a short length. Offhand, compared to normal munitions of the same type, I'd say this option cuts length to somewhere in the ballpark of 70% normal (which will have the same effect on volume). Weight would probably be a bit higher, but leaving it unchanged is probably acceptable. For cost, a mere mortal such as myself isn't going to be able to get a quote for military munitions, so we can't go off real-world pricing. As a general rule of thumb, however, GURPS often follows a trend of modifying cost by the square of the effect. In this case, that would mean double cost for the Telescoping option. I feel that's lowballing it, however, and would be more inclined to x4 or x5. Whether these are multipliers on top of the normal cost of ammo (so Telescoping APFSDS would be a total of x8, x16, or x20 cost, as APFSDS is a x4 modifier on its own) or if they follow the CF system (where xn is replaced by +x(n-1), you add up the CF's, then add 1 to get the multiplier; in this case, x2 becomes +1, x4 becomes +3, and x5 becomes +4 - so Telescoping APFSDS has a total CF of +4, +6, or +7, for x5, x7, and x8 CPS, respectively).

[GURPS Fox]

Originally Posted by Varyon

It looks like you have the mass and volume already, although your mass doesn't match any of the ones I can find here. The thing that looks to be unique about these rounds is their telescoping design that allows them to have a short length. Offhand, compared to normal munitions of the same type, I'd say this option cuts length to somewhere in the ballpark of 70% normal (which will have the same effect on volume). Weight would probably be a bit higher, but leaving it unchanged is probably acceptable. For cost, a mere mortal such as myself isn't going to be able to get a quote for military munitions, so we can't go off real-world pricing. As a general rule of thumb, however, GURPS often follows a trend of modifying cost by the square of the effect. In this case, that would mean double cost for the Telescoping option. I feel that's lowballing it, however, and would be more inclined to x4 or x5. Whether these are multipliers on top of the normal cost of ammo (so Telescoping APFSDS would be a total of x8, x16, or x20 cost, as APFSDS is a x4 modifier on its own) or if they follow the CF system (where xn is replaced by +x(n-1), you add up the CF's, then add 1 to get the multiplier; in this case, x2 becomes +1, x4 becomes +3, and x5 becomes +4 - so Telescoping APFSDS has a total CF of +4, +6, or +7, for x5, x7, and x8 CPS, respectively).

Thanks. Also, the 45mm was a joint venture between AAI and CTAI, surprisingly enough. Never went through because the Cold War ended.

[GURPS Fox]

Ok, to be honest, finding info on the weapon is frustrating because some of the links I've seen have... problems.

https://preview.redd.it/ni47has44q8a...=webp&755f27b8
Link to Reddit thread with some links that are having problems...

So, if this is any indication, the 'traditional' case version of an APFSDS would be 3,910g if the 735g lighter (or just under 19% lighter) comment in the advert and the 3,175g CTA round laid out in a report is the APFSDS are accurate.

... said 3,175g CTA round is yeeting a 755g projectile at 1.35km/s (which, if I'm not missing anything, is usually seen in autocannon APFSDS rounds)... or just short of 688kJ of kinetic energy out of the barrel. Using the equation 0.6*SQRT(KE/cal^0.4) I get 232.43577184579088410385864405914, which divided by 3.5 is 66.410220527368824029673898302611 (6x11)... which lines up with V2e's 45mm 'medium' barrel using APFSDS(R), if only off by three dice (7x9). Huh, that's weird how the damage almost lines up like that.

Also, the traditional case version of the 45mm CTA had to be on steroids or something...