The caliber of a bullet influences its terminal effect. However, on the bullet side we must also consider impact velocity, amount of expansion (both inherent and by design) and stability. For example, a bullet that could be induced to tumble on impact may produce a larger wound channel than a larger caliber (but possibly shorter).
We must also consider the vast range of influences on the target side. Point of impact, impact on bones, the exact path the bullet follows etc.
Simply put, a larger diameter bullet contributes to satisfactory performance but caliber alone does not guarantee this performance. I bet most people here use hollow-points for SD, this is an example of design modifying terminal performance. The dirty secret is that a hollow-point can sometimes reduce terminal performance - it all relates to the impact velocity of the bullet relative to the design of the hollow-point.
dgrenthum,
If i am shooting at a target with .17 rimfire and miss right by .15" well that sucks but if i am using a 45acp and hit that exact same spot i have no longer missed the wider bullet would catch the target. It would put that paper straight out of its misery.
Interestingly, that same argument was used by the FBI in the selection of the 40 S&W. It is difficult to defend though. You are shooting a pistol with which you normally make 4 inch groups under anything like realistic conditions and you hope that your neck will be saved by a few thou. more bullet diameter - Gulp!!!!
The effect of any bullet wound contains a large element of luck. That is why you hit the target once, and then again and again and again, until the threat goes away. On paper, scoring the cut on the target ring may help you gain a point. You should be so lucky in combat.
Thanks Seenterman,
I have been trying to point out that caliber is not the only factor. Bullet design contributes as much to stopping power. Blood loss is not the only, or the best, way to stop an attacker. The correct level of nerve destruction is more effective. It is just much more difficult to accomplish nerve destruction because of the accuracy requirement. If you went for a COM shot, got the left and right perfect but hit 6 inches too high - bingo, spine, game over.