Deer are extremely light skinned, light boned and easy to kill. They are more effected by "shock" than other types of heavier animals and that is why you can get away with killing so dramatically them with sub caliber poodle shooters like a .243.
However even with a deer you better be right on with your shot placement and the angles better be just right with a pip squeak 6MM because I don't care what you're shooting out of it the little guy does not have the mass and the weight to go very deep if encounters tough material like bone.
Therefore if you are going to hunt big game with 6MM use the toughest bullet with the best SD you can find. Either that or you need to be rabidly disciplined about waiting for the perfect shot presentation. And I just don’t see where that is an advantage in anyway shape or form when rifle hunting. If you want to limit yourself use a bow.
When it comes to big animals shock and energy don't mean squat. Penetration and bullet diameter/weight is the ONLY thing that matters. I've seen several cape buffalo take ungodly powerful rounds like .458 lots &.470 NE in perfect heart lung shots and just trundle off like nothing happen. They don't even hardly flinch. The only reason that they die is from bleeding out from the penetration of the bullet or a CNS disconnect.
I’ve seen hogs take a .375H&H through the lungs and not show any sign of a hit until they flopped over 100 yards down the road. I’ve also seen a hog take several .243 rounds to chest run off and not be recovered. Some animals are more prone to shock and velocity than others. I’ve seen a deer take a 100 gr soft point through vitals from a .257 Weatherby that absolutely exploded the heart and lungs and left a orange sized exit hole run into thick cover and travel for almost 200 yards before it died. I’ve seen a pronghorn take a 180gr BST through the goods from a .300 Weatherby moving at over 3200 fps. The round entered the just in front of on shoulder exited just behind the off shoulder and literally blew a bowling ball sized hole out the off size. The poor little old antelope buck turned and ran for over 100 yards with no heart of lungs left. You couldn’t have physically dumped more energy into that poor old goat yet he didn’t drop on the spot. There is NO surefire formula when it comes to velocity and expansion to guarantee an animal drops in it’s tracks. The only way to assure that is by shot placement. You want them DRT every time then hit them high and forward in the shoulder. And use a good reliable deep penetrating bullet of heavy for caliber weight.
I'll take controlled expansion, penetration, diameter and weight over macho velocity and explosive expansion any day on any big game including deer. And Ballistic tips are for tourists not for hunters.
The .243 should be considered the minimum for deer sized game IMO just like the .375H&H is the minimum for DG. They both are very successful killers of game but they have their limitation which need to be realized and taken into account.
