I think that the rule of 1000 ftlbs of energy applies more to smaller calibers where the energy figure is achieved with higher velocities. Even if a .44 or .45 caliber bullet expands only a small amount, it still punches a larger hole. I might be oversimplifying,but if you do like Head0001 says and you compare the .45 colt with the .45-70, don't you wind up with a .45 caliber hole that goes completely through the deer? I don't think that it's so much how much energy the bullet has, but rather how much of that energy is expended in the animal. A .45 caliber bullet with a large metplat is going to transfer the energy it has to the deer's body. To get a true energy figure shouldn't you subtract the remaining energy when the projectile exits from the energy before the hit, I bet that a .45 slows down a lot more in the animal than a bullet from a 30-06.