A 338 with a 300 gr bullet is where I'm comfortable with a shoulder shot, they will clean an elks clock if you get lower into the heavier shoulder, they remove section of spine and work very well, not my everyday shooter though, the percentage of guys packing a large 338 with 300's as their all round elk rifle is small, very small.I'm not sure, but I think you meant that you've seen elk hit in the hump above the spine. If so, that's not a killing or incapacitating shot, and you're right. But if he's hit in the shoulder about 2/3ds up, that goes under the spine or hits the spine. The round will take out the nerve plexus or possibly break the back with impact. It will damage the spinal cord and kill or incapacitate the animal. The actual wounding data is present on BallisticStudies.com. That's what the guy that started this blog did. jrock said that part of the bullet was even lodged in the spine. Part exited the off shoulder. Hitting the spine with a 300 grain .338 bullet even at 700 yards should have either broken the spinal cord or crushed it from blunt trama, and probably didn't do the vertebra he hit any good, either. You may not like a shot like that, but sometimes its what you get, and its still a good place to hit, as long as its not too high.
If your targeting the spine you might as well save meat and lessen the chance of wounding and pull up on the neck, target is basically the same size and it's a hit or miss deal, I've bunched up a good number just neck shooting them and they are dead before they hit the ground, no twitching or pulling themselves around with their front end.
You have to direct hit the spine to have it work every time, I've seen so many close to the spine hits have a short term effect of awesomeness then your wondering where your elk is when you get there. A perfect killing high shoulder shot is a precision target with little error but I don't want to just knock something down then kill it later, I want an animal to tip over because there is no blood left to pump or a broken pump, that's not recoverable and they are always right where you see them tip.
I really hate to mess up that much awesome meat, average shoulder shot elk will cost about 16 lbs of meat, I'm not pulling the trigger to throw meat away, I've personally lost more lbs of meat thinking the shoulder shot was thee shot and after observing a lot of elk shot in fields then helping guys recover them the only reason I'll do it any more is to try to stop an elk that is wounded, maybe one just to test a bullet but other than that it's just such a waste and a lower percentage shot.