Calculating HP from Mass (alternate scaling)

[JCurwen3]

The average HP for living things is calculated via the formula 2 x cube_root(mass_in_lbs). All of the animals in Basic Set have ST and HP based on this, and humans work comfortably with this formula as well.

There is an alternate rule option in the article Eidetic Memory: Extreme Damage, by David L. Pulver (Pyramid #3/34: Alternate GURPS, p. 25) that uses 0.85 x sqrt(mass_in_lbs) for HP instead. It states that this was the way HP were scaled in an early draft. Humans have the same values for this formula as well.

The reasons given for not using this (aside from "not scaling as neatly with length") was that it made large animals "too resilient", and small animals "perhaps a bit too weak". The examples given were a heavy warhorse ending up with HP 37 instead of HP 25, and a house cat getting HP 3 (instead of HP 4).

I'd like a reality check on that. Is HP 37 for a heavy war horse less realistic than HP 25 in terms of the animal's killability? Or HP 93 vs HP 45 for an elephant? Or HP 3 vs HP 4 for house cats? I guess I don't know if it should be 2.5x harder or 3.7x harder to kill a heavy war horse than a human. The cat HP value of 3 (actually ~2.69) sounds more right to me than 4 though (not that I've tried to kill any cats!).

I'm trying to figure out if the alternate method of scaling HP according to square of mass was abandoned due to unrealistic normal animals' HP, or if it was more for gameplay reasons (making small pets harder to kill, making large animals easier to kill, and scaling more neatly with length).

Any thoughts?

[vierasmarius]

One method of reality-checking this is to compare the damage of "Elephant guns" to the HP of an elephant. High Tech has a few examples, such as the 8-bore Greener Elephant Rifle (6d+2 pi++) and the later .600 H&H Double-Express (5dx2 pi++). That's an admittedly broad range of damage potential (between 46 and 70 on a Torso hit) but at least gives us some numbers to work with.

A standard GURPS elephant with HP 45 would likely be incapacitated by a single shot from the smaller gun. With the higher proposed HP values it would take 2 solid hits to achieve a similar result, and even the heavier gun would be unlikely to manage it in one hit. A skilled hunter might be aiming for the Vitals or Skull, though, making a one-hit incapacitation feasible.

So, I guess we need some real-world data now. What were the kill rates like for these various sizes of rifles? Did it regularly take two or more shots from even the heaviest rifles to take down an elephant?

[starslayer]

Originally Posted by vierasmarius

So, I guess we need some real-world data now. What were the kill rates like for these various sizes of rifles? Did it regularly take two or more shots from even the heaviest rifles to take down an elephant?

No/yes- It normally only took one shot, from a very skilled hunter, who was using a bi-pod/tripod brace, could spend a lot of time aiming up, and then shot for the vitals. (since elephants don't really fear people at 100+ yards overmuch). As I understand it if you missed a vitals hit with an elephant gun the elephant ran away and was unlikely to die or even bleed excessively, or the elephant charged and you either ran faster or died.

[vierasmarius]

Originally Posted by starslayer

No/yes- It normally only took one shot, from a very skilled hunter, who was using a bi-pod/tripod brace, could spend a lot of time aiming up, and then shot for the vitals. (since elephants don't really fear people at 100+ yards overmuch). As I understand it if you missed a vitals hit with an elephant gun the elephant ran away and was unlikely to die or even bleed excessively, or the elephant charged and you either ran faster or died.

That seems consistent with the higher square-root-based HP. A simple Torso hit from the .600 won't inflict sufficient injury to incapacitate, but a Vitals hit will (70 and 105 average injury, respectively, versus HP 90+). With the older Greener rifle, you'd need to make a skull hit to have a chance of 1-hit take down (with skull DR, it'll take a good roll to exceed 90 points). Which may be why it's a double-barreled gun, giving an extra chance for a kill.

With the RAW numbers, an average Torso hit from either rifle would immediately drop the elephant below 0 HP, resulting in incapacitation in seconds and death from bleeding out (or a follow-up shot) shortly after. It sounds like that was not the expected result of an imprecise hit.

[gilbertocarlos]

Originally Posted by vierasmarius

That's an admittedly broad range of damage potential (between 46 and 70 on a Torso hit) but at least gives us some numbers to work with.

38 and 62 actually.

[Bruno]

Originally Posted by vierasmarius

Which may be why it's a double-barreled gun, giving an extra chance for a kill.

You don't fire them both at once though. That's so you don't have to stop and reload while an enraged, wounded bull elephant is charging you.

[Fred Brackin]

Originally Posted by JCurwen3

The average HP for living things is calculated via the formula 2 x cube_root(mass_in_lbs). All of the animals in Basic Set have ST and HP based on this, and humans work comfortably with this formula as well.

Humans work "well" with this formula as long as they seldom have ST/HP higher than 12 and never higher than 14. Above these levels they cause the whole system to fracture.

Things can get even wiorse when you start adding non Harshly Realisitic rules options. For example, a Sumo Stylist from Martial Arts is allowed to buy a Perk that gives him the ability to buy HP to 100% greater than ST if he weighs a lot.

So a 400lb (actually 340 lbs minimum) Sumotori with ST 20 could have 40 HP, only 5 less than an average elephant who's probably 20x heavier. Power Ups 2:Perks would allow even higher HP totals with no wieght increase.

So i think, yeah we either all become really severe Stat Normalizers or we rescale HP for non-humans or maybe we all just tiptoe around this issue and hope it never comes up in our particular games.

[Bruno]

Originally Posted by Fred Brackin

Humans work "well" with this formula as long as they seldom have ST/HP higher than 12 and never higher than 14. Above these levels they cause the whole system to fracture.

Or looking at it from another perspective, as long as you assume Andre the Giant, the Great Kali, and various others (all weighing over 400 lbs, over 7 feet tall, and very strong) are no more than ST 15, HP 15. I've done math on the forum before, and I'm quite happy with rating Arnold Schwarzenegger at his physical peak at ST 14 with a modest Lifting skill - and he was pretty significantly smaller than some of these very large men. The top participants in the Strongest Man competitions are 400+ lbs with lots of muscle, and if they're only ST 15 HP 15 I'll go buy a hat so I can eat it.

If GURPS is supposed to be calibrated so human ST ranges all the way to 20 (it's stated to be so, and the lifting/encumbrance rules back it up) then these extremely physically fit individuals should be producing higher numbers.

Now, there's ways to do that, but there's questions on how whichever formula is used that need to be answered.

How fit is the hypothetical creature assumed to be? Average 20th century city dweller (without Overweight)? Average pre-TL5 human (who will be a rural agricultural worker)? Are we talking something roughly corresponding to the theoretical concept of BMI 18-25 (ignoring for the moment the 'non average' builds that make BMI only a very vague approximation)?

It would take something on the order of "adjusting for conditioning with plus or minus 35%" for the standard calculation to bump up those strongmen into the high teens. The alternate calculation gives numbers for those 380-440 lb strongmen that require much smaller error bars.

[Purple Haze]

"Elephant guns" are for the wealthy tourists. The professional ivory hunters did not use them.

The vast majority of elephants killed throughout history have been one-shotted by a 6mm or a 6.5mm to the brain. The third most common caliber was 7mm.

[RyanW]

Originally Posted by Purple Haze

"Elephant guns" are for the wealthy tourists. The professional ivory hunters did not use them.

The vast majority of elephants killed throughout history have been one-shotted by a 6mm or a 6.5mm to the brain. The third most common caliber was 7mm.

7.62x39 has become the predominant chambering for the ivory trade of the last 50 years or so.