How to Stat Ghost in the Shell Style Hypervelocity Ammunition

[Varyon]

Originally Posted by The_Ryujin

3 times the damage from boosted velocity means that the bullet is traveling 9 times faster!

GURPS firearm damage typically scales linearly with velocity, so 3x damage is 3x velocity (or, rather, given we were looking at starting with velocity, it’s that 3x velocity means 3x damage). And as I got that 3x figure starting from a weapon that has a muzzle velocity of 350 m/s, you’d want to set your damage based on that; as 350 is the typical 9mm velocity, and 2d+2 pi is, IIRC, the typical 9mm damage, you’d triple that, for an average of 27 pi - which is 8d-1 pi.

That’s still pretty crazy; I’d expect a weapon that is designed for it would have a lot of weight and probably a long bolt; if dude’s SMG had been using such monstrous rounds, it probably would have burst apart during the first salvo, rather than being able to at least fire a couple more magazines of normal ammo (but the way it treated cover implied it might have still been using HV).

[Fred Brackin]

Originally Posted by Varyon

GURPS firearm damage typically scales linearly with velocity, so 3x damage is 3x velocity (or, rather, given we were looking at starting with velocity, it’s that 3x velocity means 3x damage).V).

Yes, to triple damage triple velocity. There is a 9x in there because 3x velocity means 3x kinetic energy but Gurps buries that piece of math.

Speaking of buried complexity I've been ignoring things like the direct blowback mechanism Uzis and most other SMGs use. That probably wouldn't handle the 3x rounds very well. You'd be lucky if it only jammed.

[The_Ryujin]

Originally Posted by Varyon

GURPS firearm damage typically scales linearly with velocity, so 3x damage is 3x velocity (or, rather, given we were looking at starting with velocity, it’s that 3x velocity means 3x damage).

Yeah, had a brain fart there. I meant to say 9 times the KE.

[GURPS Fox]

Originally Posted by Fred Brackin

None of it is "practical". You might be aiming more at "physically possible".

1600 meters per second might be that physically possible limit for anything even vaguely like gunpowder. Some rifles would hit that limit at around 1.5x. P

As far as I know, the absolute limit for 'conventional' gunpowder (i.e., nothing that uses things like electrothermal chemical propellants) is 1.8km/s.

Originally Posted by The_Ryujin

3× is kinda crazy, like TL 10 ETC might justify 1.5×. 3 times the damage from boosted velocity means that the bullet is traveling 9 times faster! Now if you want to get crazy you can say that HV ammo is as good as 1st gen ETC ammo (1.25× damage under the current draft and fits my research) and treat them as APFSDSDU rounds. APFSDSDU gives a AD (2) and boosts damage by 1.7× (from a combination of higher muzzle velocity, density and lower crosssectional area) and doubles range but reduces pieing damage by 1 step. I'd also have HV ammo worsen Malf. by two steps unless the gun is designed to fire them (maybe 1.5× cost).

Let's take a 9mm round fired by an Uzi which is 3d-1 which averages 9.5 pts of basic damage. This becomes 9.5 × 1.25 × 1.7 or ~20.2 pts (!) which translates into 6d-1 (2) pi-. With this HV 5.56mm will become 10d+2 (2) pi-. This will give you a nice cinematic HV feel.

... wow... that's a lot of good information. This is why I like the GURPS community. Ask a question, and you'll have people showing up with the context and answer.

Originally Posted by Varyon

GURPS firearm damage typically scales linearly with velocity, so 3x damage is 3x velocity (or, rather, given we were looking at starting with velocity, it’s that 3x velocity means 3x damage). And as I got that 3x figure starting from a weapon that has a muzzle velocity of 350 m/s, you’d want to set your damage based on that; as 350 is the typical 9mm velocity, and 2d+2 pi is, IIRC, the typical 9mm damage, you’d triple that, for an average of 27 pi - which is 8d-1 pi.

So stronger than conventional 7.62NATO if we use the 3x modifier.

That’s still pretty crazy; I’d expect a weapon that is designed for it would have a lot of weight and probably a long bolt; if dude’s SMG had been using such monstrous rounds, it probably would have burst apart during the first salvo, rather than being able to at least fire a couple more magazines of normal ammo (but the way it treated cover implied it might have still been using HV).

Given Ghost in the Shell metaverse's general semi-rediculous materials science (the musculature of cyborgs are CNT muscle alone and can do things like take at least 200-meter drops and two M67 hand grenades at point blank with ease), it is likely that the weapon only fared as well as it did because it was a more modern version using modern materials. If the perp used an older model, it would have gone kaboom.

At least I'm not going full-on 6Commando (a webcomic based on Ogre, whose battlesuit weapons fire rifle rounds at roughly 3km/s using some hybrid of conventional rifles and gauss called 'mag-boosted' guns)...

[Rupert]

Originally Posted by GURPS Fox

As far as I know, the absolute limit for 'conventional' gunpowder (i.e., nothing that uses things like electrothermal chemical propellants) is 1.8km/s.

It has to be higher than that, because modern tank guns reach that and they have massive muzzle blasts, so there's plenty of energy and pressure still in the propellant gasses.

The Russians are claiming a little over 2 k/s for their new 125mm gun and ammo, but that being hype and exaggeration is quite possible.

[GURPS Fox]

Originally Posted by Rupert

It has to be higher than that, because modern tank guns reach that and they have massive muzzle blasts, so there's plenty of energy and pressure still in the propellant gasses.

The Russians are claiming a little over 2 k/s for their new 125mm gun and ammo, but that being hype and exaggeration is quite possible.

From what I gather, by 1.8km/s you're getting inefficient when it comes to things like powder burn (think the M551 Sheridan's caseless round problem, the powder didn't burn efficiently enough, and it caused problems like cookoff while you load a new round in). In addition, you could only get 2km/s with sabots, and even then, you'll start to get inefficient.

So, here is an 'HV Ammo Ruleset' I've cooked up with your guys' input:

• HV Ammo is only available to 'conventional' guns built using tech from TL8 or later.
• HV-compatable weapons have a 1.1x weight multiplier to simulate the added features to make the weapon take the pressures and punishment of an HV round.
• In ANY Non-HV TL8 or higher weapon that uses HV Ammo, increase the Malf. by two steps in the initial magazine and increase Malf. by one step per additional magazine. If the weapon is made at tech levels less than TL8, turn the weapon and magazine into a grenade of similar weight (to simulate a catastrophic cook-off).
• Base ammo (i.e., FMJ/Solid) is 1.25 times the damage and range. All rounds have a 1.5x modifier to the cost of the round. Example: a 5.56NATO round from an HV-compatible M16 rifle will get a damage roll of roughly 6d+1 instead of the usual 5d.
• Other modifiers (like ETC or saboted ammunition) can be applied to HV ammo.

[The_Ryujin]

Originally Posted by GURPS Fox

From what I gather, by 1.8km/s you're getting inefficient when it comes to things like powder burn (think the M551 Sheridan's caseless round problem, the powder didn't burn efficiently enough, and it caused problems like cookoff while you load a new round in). In addition, you could only get 2km/s with sabots, and even then, you'll start to get inefficient.

So, here is an 'HV Ammo Ruleset' I've cooked up with your guys' input:

• HV Ammo is only available to 'conventional' guns built using tech from TL8 or later.
• HV-compatable weapons have a 1.1x weight multiplier to simulate the added features to make the weapon take the pressures and punishment of an HV round.
• In ANY Non-HV TL8 or higher weapon that uses HV Ammo, increase the Malf. by two steps in the initial magazine and increase Malf. by one step per additional magazine. If the weapon is made at tech levels less than TL8, turn the weapon and magazine into a grenade of similar weight (to simulate a catastrophic cook-off).
• Base ammo (i.e., FMJ/Solid) is 1.25 times the damage and range. All rounds have a 1.5x modifier to the cost of the round. Example: a 5.56NATO round from an HV-compatible M16 rifle will get a damage roll of roughly 6d+1 instead of the usual 5d.
• Other modifiers (like ETC or saboted ammunition) can be applied to HV ammo.

Looks Good. HV guns should also weight at lest 1.1 and cost 1.5 to 2× as much to cover the stronger barrel and chamber.

[hal]

Been away for vacation and am back - will look into what goes into a Hypervelocity 9mm round in order to get a given damage value based upon:

a) a given bullet mass
b) a given velocity range

Will likely do this sometime tomorrow...

but just to give you an idea...

9mm 124 grain bullet with a velocity of 1140 feet per second - results in a GURPS 4e damage rating of 2d6+1 based on the spreadsheet.

Were we to get its muzzle velocity to 3240 feet per second, its damage would be 7d+1. At those speeds, you may see its accuracy improve a little over that of ordinary bullet rounds.

[Anthony]

Originally Posted by Rupert

It has to be higher than that, because modern tank guns reach that and they have massive muzzle blasts, so there's plenty of energy and pressure still in the propellant gasses.

That doesn't actually follow -- the limit is not a function of available energy, it's a function of gas velocity, so it's possible to have plenty of energy that's still in the gas but not actually available for propulsion, or that might theoretically be available but in practice is extremely inefficient to extract.

[Fred Brackin]

Originally Posted by hal

. At those speeds, you may see its accuracy improve a little over that of ordinary bullet rounds.

Real world things maybe Gurps 4e stat ACC, no. 4e ACC is almost totally determined in 4e by gun format (pistol/rifle/etc). In 3e yes ACC was derived from range in 3e.