All GURPS damage has three parts to it, even if much of the time they’re implicit.

In order of how it’s applied, which is our first point of potential controversy!
1) Armor divisor. Yes, on a hit and a failed defense if one is allowed, the first thing you probably do as ask “how much armor, if any, is facing me.” If the answer is zero, you don’t do any math, and proceed directly to step 2. But the first thing you do is check to see if whatever DR (Damage Resistance) you’re facing, and reduce or increase it based on the type of attack you’re making. This can be a property of the damage type (some armors get altered stats vs. crushing, piercing, cutting weapons) or a property of the weapon itself (magic or high tech armor divisors, blunt tips or soft construction)
2) Basic Damage. This is the raw oomph of the attack. As discussed in a few places, this can be looked at as a raw ability to penetrate armor. I will assert that it is not yet a measure of wounding and injury. Yet. Basic damage is calculated as a function of the square root of Kinetic Energy for guns, the cube root of KE for most beam weapons, is optionally sqrt(KE) for bows (The Deadly Spring) or uses the strength plus adds model (thrust and swing) of melee weapons and muscle-powered ranged weapons.

3) Wound type, depth, and size. Finally, we get to put the hurt on. The damage here is given its true type, and some sort of multiplier is applied. Tiny bullets that are also slow get pi-, and injury is half penetration. Cutting weapons increase damage by 50%, while my least-favorite damage type, impaling, gets its penetration doubled for injury.

These three things are very, very useful, and have pretty good definitions, for firearms especially. But before we do that, why three? Why not just combine either the first and second two numbers? So instead of a gun (again, best maps to these three) that does 4d (2) pi-, which penetrates like 8d but wounds like 2d, why the frack don’t you just have something like 8d {4} – and note the curly brackets.

That’s Dougish? Hamptonian? I like Hamptonian. That’s Hamptonian for “what is in these brackets refers to wounding.”

Anyway, that might mean “roll 8d for penetration, but divide penetration by 4 for injury.”

You could also just write 2d (4), with the conventional sense used in GURPS, for “this will do 2d injury, but divides any armor by 4.”

Both have a nice symmetry and sensibility to them. So why make things more complicated? As +Peter V. Dell’Orto likes to say, “Where’s the Awesome?”

Back to guns, because they map well. Each of these things represents a very distinct set of properties.

Let’s start with #2. The raw damage (penetration) rating of a gun – or more exactly, it’s projectile – is determined as a function of only two things: the kinetic energy of the bullet and its caliber. If you fire a 10mm diameter chunk of anything with 720 Joules of energy, you’re going to get about 3d+1 damage (the official formula used by +Hans-Christian Vortisch and +David Pulver might come in at 3d; regardless, given those two things, that’s what you get).

But what if that projectile is made of tungsten carbide? Or generic copper-jacketed lead? Or hell, maybe it’s a frozen 10mm marshmallow.  What if, instead of a blunt pistol bullet, it’s shaped more like a spike than an ogive? If the projectile is strong enough to survive delivering it’s own energy content (this may be, after some analysis, why the real-world data for the 55gr 5.56x45mm only penetrates 5d instead of the 5d+1 or 5d+2 my calculations suggest . . . the energy it carries is enough to overwhelm the cohesion of its component materials, so it can’t effectively deliver all them joules. Certainly it can’t be because my Excel spreadsheet model is wrong. Nah.)

That’s where #1 comes in. It can separate out the effects of hardness and geometry from raw energy. Because you might want to do that, since energy is a useful thing to know, especially when it comes to breaking up homogeneous objects.

OK, you’re through the crunchy shell. Now you’re in the chewy center. If that projectile fragments, or just pokes a thin hole, it might pass through a body without doing much permanent damage . . . or the wound could be terrible and grotesque (and if you’re read DiMaio you’ve seen some gross stuff) because the energy is all used to destroy, rather than stretch, heat, or harmlessly displace tissue.

So some sort of efficiency factor that gives the size of the wound channel relative to energy content is useful. This is especially true when you relax our caliber restriction. If you have a high-energy, high caliber weapon that penetrates like 4d, and a finned, hardened, skinny dart, that also penetrates like 4d, but really is 2d(2), the first might be something like 4d pi++, where it wounds like 8d. The second might even be 2d (2) pi-, where it destroys objects like 2d (due to energy dump if it doesn’t blow through), but in humans, really only delivers a 1d wound.

For hand weapons, you could easily see the use. If you’re trying to overwhelm the armor of something, having it hard, perhaps magically hard, will amplify the basic energy you can put into swinging a weapon. If you are ST 14 (about twice as powerful as an average schmo in GURPS), and swing a 2-lb. stick where most of the weight is in the head, you can write down something like “swing 2d” on your character sheet. If that weapon head is concentrating force into a tiny area, like a pick or war hammer, you could perhaps note that by giving it an armor divisor. So the war hammer might do 2d (2), which is kinda a lot, but you could also impart fractional armor divisors if you love math and hate your fellow players. Or if you use a computer. But when that pick sticks into you, if it’s really long, you can see that might be awful. If it’s maybe short and pyramidal, it might punch the armor fine, but not reach deeply enough inside you to really rock your world, internal-organ-wise. (This is unlikely to be true, since your ribcage will deform under impact, allowing the beak to reach the center . . . unless you are deforming more armor to do that, in which case the wound could be very shallow.)

If you put an axe-head on it, you can see that spreading out the force into a long line will be bad for penetration, increasing the effect of armor. That might be an armor divisor of (0.75) or something. Perhaps even more, like (0.5). But you can also see that the wide wound will be truly awful on an unarmored person.

I personally think that having both armor divisors and wound severity modifiers makes a lot of sense, and that both are useful. Certainly, if one were to ever come up with a meta-system that integrated hand weapons, blunt trauma, bullets, bows, sharp sticks, and harsh language into one black box that output GURPS weapon stats, I could see a real utility to allow more moving parts rather than fewer, both for nuance as well as resolution.

4 thoughts on “Damage Dissected

    1. tbone already had something called GUTS on his site. Thus GUST.

      But as it turns out, I'm misremembering, and his is called GUTHS.

      I like Grand Universal Smackdown Theory, though.

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