I live in Alaska. Availiability is a problem here. I carry two calibers when I go out of town, 30-06 and .338 Win Mag. Every small town store and villege trading post will have those two calibers. They will also carry 30-30, .223, and maybe .300 Win Mag, don't count on anything else. Those new whiz bang little magnums, you forget, lose, or run out of shells, you got an expensive club. Oh you can find plenty of ammo in Anchorage, or Fairbanks. But get out in Rural ALaska and they are just not there.
Some of the new cartridges are designed for the inherant weakness of a certain platform system. Yea, alloy ARs can't handle the pressures of a good old 30-06, nor the length. Now great strides have been made in powders, allowing the development of these new cartridges. They can take a smaller cartridge and do great things with it. What will that same technology do with the old cartridge. Instead of making new cartridges, why not improve the old ones. Weatherby came out with the idea of the 30/378 and .338/378 back in the 60s, but the powders was not availiable back then to power those big powerhouses. Today look at what they can do.
What do we hunt in this country, Whitetail, Mulies, Antalope, Elk, Moose, Caribou, Black Bears, and Grizzly/Brown Bears. You don't need or want a semi auto for these animals. Now Hogs, Wolves, Coyotes, and other varmits, a semi auto is OK and in some cases needed. But far too often with semi autos a shooter will spray the area, instead of aiming and making a killing shot. I found that out while in the military.
Now I will say the strides in new scopes and range finders has been great. Look at what I do. I carry a .338/378 Weatherby, with a 3.5X15X50 Night Force scope. I use a leupold lazer range finder. By using the range finder to determine the range, and dialing my scope to match that range, I am able to kill Moose, Caribou, and Bears out at ranges I would have never dreamed of 30 years ago. I'm a crippled up old man, stalking is not always an option.
I pick off a Feral Cat once in a while too.
Both my hunting partners have .50BMGs, they are trying to talk me into getting one as well. I've shot the Barrett and liked shooting it too much. I can not afford to feed that thing.