I've read the suggestion that 'damage' would best be measured by Kinetic energy at impact divided by the cross sectional area of the bullet as this is the best 'simple' predictor of cavitation (the size of the hole inside the target). Although an admittedly 'opinion rich' area, I was wondering if you had any thoughts?
Yeah, lots more heat than light IMHO.
From my limited research, bullet lethality is largely a function of hitting (and reaching) a vulnerable organ. Anecdotally, big bullets like the .45 Auto were developed to knock down targets.
And most vulnerable organs are relatively well-protected by bone, muscle and tissue. Thus, it seems to me that bullets with greater penetration are more likely to reach a vulnerable organ and overall more lethal. I recall reading a very persuasive paper that argued this very point, but I don't have a cite handy.
Your suggested equation seems likely to me to calculate relative penetration. So the approach might well be valid. If I understand your proposal, if KE is constant, a smaller diameter bullet would yield a higher value. Intuitively, a smaller bullet with the same energy should go deeper.
That said, raw kinetic energy seems to be a better overall predictor of antitank weapon penetration, which may or may not be applicable to small arms.
In any case, I do not think that calculated "penetration" (or kinetic energy) bears a linear relationship to damage. I.e., I don't think a number twice as high indicates twice the "damage". In fact, for reasons I've stated in other posts(1), I don't think that hit points are actually a very realistic way to model gunshot wounds. Paradoxically, I think that they work quite well in RPGs, though.
Maybe the best use of things like muzzle energy and bullet diameter would be to rank bullets against each other, rather than produce some kind of mathematically precise "damage" rating.
(1) It is interesting, by the way, to consider real world gun combat examples when talking about RPGs. In the famous Gunfight at the OK Corral, 20-30 shots were fired, mostly from pistols at 10 feet or less. There were 9 hits (not including the shotgun blast that hit Tom McClaury), implying an overall hit rate of abour 30-50%. However, the real "to hit" percentage might be lower, as Billy Clanton was hit 5 times in rapid succession (he may not have been dodging effectively after the first hit) and Tom McClaury was shot once while collapsing from the shotgun blast. In CT (and Striker) these men would have hit their target 83% of the time (5+ on 2d), before adding any skill or advantageous DEX modifiers.
Frank Chadwick, in "Lethality in Roleplaying Small Arms Systems", analyzes a number of gun battles between US police and Mexican gangs on the US/Mexico border. They were using revolvers and a few shotguns. Some interesting conclusions:
--US police fired 90 shots and hit with 29.
--a "...total of fifteen officers and suspects were wounded ...and they were hit by a total of 32 bullets. Most of the injured men were struck by a single bullet; four were struck by multiple bullets, and of these one was struck by eight bullets. Of these fifteen casualties, 2 were killed almost instantly while the other thirteen survived and recovered. All of those who suffered multiple gunshot wounds recovered. That is, none of the fatalities were caused by a cumulative build-up of trauma, but rather were due to a single, almost instantly fatal, wound."
--In terms of fatality, only 1 of the 11 chest wounds were fatal (!), the single head wound was fatal, and none of the 4 abdomen wounds were fatal.
