Reposted from a similar 2010 thread.
I have either killed or witnessed the killing of maybe 40 deer, with everything from service pistol calibers (above 9mm) through the classic bigbore revolvers, centerfire rifles from .223 through 45-70. Oh, 12 and 20 gauge slugs, too.
FWIW the only 'instant kills' I have seen have been when the bullet destroyed the spine at the shoulder- as in 'wrecked it' and sailed on through. Didn't matter if it was a 240 grain .44 SWC at 1000 fps, 150 grain softpoint from a 30-30 at over 200 yards- or a 175 grain softpoint from a long-barreled 7mm Mauser. Didn't matter if the deer were standing still or in a flat-out sprint. Bang. Flop. Skid.
Shots that took out the shoulder bone (front of the shoulder on whitetail) anchored them almost as fast, though a finishing shot was sometimes required. Broadside heart shots generally elicited about a 20 yard trot followed by a flop.
Worst shot I ever made was on a doe that goosed just as I pressed off a 300 grain .44 XTP at 1350 fps, and it landed about halfway down the back under the spine. That one was a 250 yard tracking job with a dead deer at the end.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence