I know there is such a thing as knock down power. Take a 243 and a 300win mag. take an identicle double lung shot w/ each. each deer will probably die at the same time, however the 300 will knock a deer off his feet 9 out of 10 times whereas the 243 would be lucky to get 5 out of 10. Now a mortally wounded deer still on his feet can get his oh crap I've been shot system going and cover some ground, where as the deer thats been knocked off his feet RARELY gets up. thats not to say any given caliber can "KILL INSTANTLY" , but the larger ones DO make em die closer to where you shoot em.