ORIGINAL: ipscshooter
I thought that part of the killing power of a bullet was related to hydrostatic shock and the disruption of organs not directly impacted by the bullet. Seems to me that if your .30-06 bullet expands to, say, .500 and completely penetrates the body due to its higher speed and energy, whereas the 7.62X39 bullet expands to, say .450 (because of its slower speed) and penetrates all of the body, but ends up lodged under the skin on the opposite side, the .30-06 is still going to do a lot more damage, because it's travelling at a higher rate of speed, and generating greater hydrostatic shock/organ disruption as it passes through, whereas the 7.62 X 39 is slowing down so quickly that for the last half of its trek through the body it's generating very little hydrostatic shock/organ disruption.
In doing a little "google-ing", I found this:
How Deep Can It Get Before It's Too Deep? It does not matter to effectiveness if the bullet exits. So long as it contacts something vital, it matters not a whit whether a bullet stays inside the body cavity or not. A bullet which doesn't exit and "dumps its energy" into the body, cannot kill any more effectively than one which traverses the victim and exits. The most effective bullet will be the one that expands and penetrates all the way through, taking large pieces of things like the spinal colum with it on the way out. So there is really no such thing as "overpentration" but "underpenetration" is a real problem, especially if your target can shoot back.
That's a pretty good explanation. The .223 does some substantial damage to internal organs that never touch the bullet directly. That's one thing that makes it a good combat load. Even the armor-piercing rounds that aren't designed to expand much make a mess of internal organs.
As for the .30-06 and other rounds wasting energy; that may be somewhat true from 150 yards and closer, but to get out to range and still deliver kinetic energy required to deliver an accurate shot takes a more powerful round. The 7.62x39 is a great round for deer hunting, but look at the ballistics. What is the drop on the 7.62x39 at 300 yards? It gets even worse further out, which means the round is rapidly losing energy. It isn't that the higher powered rounds are wasting energy, they just have enough juice to get the job done at longer range. I shoot a 7.62x39 single-shot and use it for deer hunting, but where I hunt with it, I'll never get a shot over 150, so it's just fine. I would not attempt to shoot at anything over 250 yards with it, and even that is stretching it's limits. Personally, I don't mind wasting a little energy if it means my weapon has greater range and therefore more hunting utility.