There are others on here that more then I, but if you check out what the best of the west guys are doing with just a regular old 7MM, thats pretty impressive and they are also doing to long shots with the 6.5X264, both of those you can get HSM ammo loaded with berger bullets. Another caliber you should also look at is the 7MM STW, not many guns are still getting 2550fps at 500 yards with a 140gr bullet.
I have a sendero 300RUM and I am really considering when the barrel is gone to get a 28-30 inch barrel and have it rechambered to a 7MM STW.
I think if you were to get a 338 edge from Shawn Carlock at Defensive edge that they sell loaded ammo too??? somebody correct me if I am wrong. Or look at the 338 Lapua Mag.
You have to remember if your in the middle of no where and run out of ammo that most of these little mom and pop sporting/general stores are only going to have probably 243, 270, 7MM, 30/30, 30/06, 308 and 300 win mag.
Have you thought much about reloading??? I personally think that when a person starts hunting/shooting that they tend to learn a little more about what they are doing if they reload, its kinda like having a computer, if you learn to build your own computer then your going to understand a little more about how the computer works. There is a lot of good advice from alot of good people here on the board.
Merry Christmas and Happy New Year.
Chuck