I shot a moose at 10 yards with a 338 Mag, 250 gr Grand Slam. It was on a trail, trotting towards me.
I did something that I always do when I fire a deer/moose shot. I carefully open the action and pick out the empty case. I am so confident in the ammo and the shot that I don't even watch the animal.
In this case the moose turned 90 degrees and took off. The fellow with me said "You missed!"
I said "NO. He just doesn't know he is dead yet." Just then we heard the crash as the moose keeled over. It had gone about 40 yards.
My confidence (arrogance) got challenged when we gutted it. I had shot straight at the sternum. I expected to see the Grand Slam punch a big hole through the heart / lungs. The chest was pristine, except for a tiny slice off the top of the heart.
My bullet had deflected and run down the side of the moose, between the hide and the ribs. It nicked one rib and a bit of rib blew across the top of the heart. But for that splinter, the moose would still be running.
To date, all my kills have been one shot kills, and the ammo has worked well - except for the Min-30 where my handloads did not chamber fully and the deer got away.
I have since learned to cycle all my handloads through the gun, just to make sure. In the case of the Mini-30, I had taken some ammo intended for a different trifle.