[Ulzgoroth]

Originally Posted by FF_Ninja

So far, just about every thought I've read about rounds has to do with varying damage - I.E. larger caliber rounds doing more "damage" than smaller caliber rounds (which, frankly, I believe is patently false).

Well good news: it is! Larger calibers may have more or less damage. There's a correlation, within a particular class of rounds (rifle or pistol) between bigger and more powerful, but it's not remotely absolute.

Larger calibers do directly correspond to higher wounding factors, in a chunky sort of way (and with an exception for small-caliber high-speed rifle rounds). This is Basic material, but particularly addressed on High Tech 163.

Originally Posted by FF_Ninja

I've yet to find anyone touch upon the nuances of what a round does after it impacts - other than the general idea which is, "getting shot sucks" (which is patently true).

Ultimately, what happens is injury, and maybe if you use the right optional rules some bleeding and (very optionally) a long-term side effect. Martial Arts has the most advanced version of the wounding rules, I believe.

What exactly happens with the bullet in the process of this is of academic interest, not game-mechanical significance. GURPS does not have a hugely detailed system for trauma.

Originally Posted by FF_Ninja

To further define the issue at hand: small caliber rounds have a tendency to tumble when they impact (resulting in more internal damage) and travel when impacting a bone, as opposed to their larger caliber brethren which generally just over-penetrate. Range is a factor, too: shoot a dude at point-blank with a .308 and it'll tend to make a clean (albeit large) hole front-to-back; the same shot at a more optimal distance would have decelerated a bit already.

Tumbling has a lot to do with the balance of particular rounds. I'm not sure size is really much of a determinant. And I'm quite curious as to whether .308 is really more likely to tumble at lower speeds?

Incidentally, both 5.56mm and .308 fall within the same division of sizing for GURPS purposes: they only are credited with pi (rather than pi-) due to high speed, which probably has to do with bullets yawing or tumbling after impact. (It does explicitly in the case of the 5.56, per Tactical Shooting p61.)

Particularly relevant rules for terminal ballistics include High Tech p162: Body Hits and the aforementioned Tactical Shooting p61. Martial Arts advanced wounding rules aren't gunshot-specific but are likely to be something you want if this is where your thinking is.

Overpenetration is in the Basic Set. It is probably overgenerous with respect to the behavior of some less stable solid bullets after penetrating one target. A bullet from an M-16 that's tumbled and torn itself to pieces isn't going to fly well past the first person it hits.

Originally Posted by FF_Ninja

I'm envisioning a situation where, say, a Russian agent with a .22LR pistol pops someone dissident the skull (old KGB style), and the round penetrates only the first layer of bone but then proceeds to tumble and travel, turning said dissident's brains into scrambled eggs. A through-and-through shot from a heavier caliber weapon wouldn't do that.

...You're really going with 'a large-caliber shot through your entire brain wouldn't be so bad' as your test claim here?

I mean, it's possible (though probably extraordinarily unreliable) for a lighter round bouncing off bone to result in more internal damage, but you pick shot through the brain for your example?

I suspect the GURPS answer to 'bullets sometimes ricochet around inside somebody's body like a deranged wasp' is 'that's a critical hit result, that is'. Bullets tumbling, fragmenting, and the like is factored directly into their wounding factor.