Don't know much about the 280, but I have a remington 700 mountain rifle ina 35 whelen, and it's a perfect factory rifle for elk... light weight, accurate and aesthetically good looking. Good buy, and good luck on finding a good load. I'd hit up the AR forum for loads if yu can't find help here.
I have the same rifle in .280 and have used it on elk. I killed one elk with it before I got my .338 WinMag. I can tell you what NOT to use. Don't use Winchester Supreme Silvertips. They were around 160g. These were different than the Ballistic Silvertips that are out there now. All I found was fragments. It was at point blank range, but still shouldn't disintegrate. Elk was still dead but I wouldn't take a chance with them again. I have also used Winchester Failsafes on mule deer. They punch through but don't expand as much as I'd like. My recommendation is to stay with the heavy-for-caliber bullets...around 160g. Good heavy construction. I like Nosler Partitions but there are plenty of good bullets out there. I have heard Barnes makes a good bullet but don't have any first hand experience with them. I took a quick look through Cabela's ammo selection and sadly, there are not a lot of heavy game rounds available for the .280. Most of what's available are 140g and 150g deer rounds. It's a shame Remington doesn't sell a .280 in their Safari grade line. It would have a Swift A-frame bullet which would be fine for elk. The 700 Mtn Rifle is a great gun for elk hunting. Easy to carry and handy. Good luck with it.
What does "gauge" mean anyway? As used here gauge means the number of round lead balls the same diameter as the inside of the barrel (aka the bore) that it would take to weigh one pound. It takes 12 lead balls the same diameter as a 12 gauge barrel to weigh a pound. The smaller 20 gauge would require 20 balls of that barrel diameter. The larger bore 12 gauge would require 12 lead balls of the bore diameter to weigh one pound.
In general the number of pellets in a shotgun shell...