No elk experience, but for moose inside 400 yards the 120 and 140 TTSX at 7mm-08 to 7 RUM velocities has been wrecking the important plumbing for friends and family. My personal choice would be the 150 Accubond but if you have a different favorite I'd use it and focus on finding elk and making a good shot.
I don't have a proven .280 load for it but in my 7mm08 and 7mm Rem my 150 NBT load has been interchangeable with only minor POI change. From my notes the .280 I loaded for shot 150 NBT's into just under an inch with IMR4350 at above my manual's max load, I'd reduce to starting and work up from there for starters.
I currently shoot hornady 139 GMX over IMR 4831 running 2950 fps. I have had exceptional results on elk and deer both. I have a small stock of these bullets but they seem impossible to get currently so I want to expand my horizons and possibly try some different bullets and powders that may be available. Thanks everyone so far for the input it has been great.
If you are happy with the monos, check out hammer bullets. I'm working with the 143gr hammer hunters and Viht N165 currently in an AI build. I would think the 150 gr shock hammer would be fantastic for 400yds and under.
I've used 57.5 grains of RL22 with the Hornady SST with great luck. Some say the SST is too soft, but I've had mostly pass-throughs and a few under the far side hide. It's a pretty hard hitting load that approaches 7 Mag velocities.
I have a load for my Remington 700 Mountain LS using a max load of RL19 and 140 AB's that I would not be afraid to use on an elk. I have only shot it to 300 yards but it is very consistent out to that distance. I have a box of 160's that I always wanted to try to work a load up with but the 140's are so good I am having a hard time changing.
Interested in all the options you guys are throwing out. My daughter drew youth az cow this year and the kids rifle is a 280. Right now we are shooting Berger 150 gr. Classics with h4831sc. Ordered some 140 Barnes ttsx from powder valley early this week also. Have some hybrid 100v I would like to try in this 280 too.
My deer load last fall was 168 Berger classic hunters over Reloder 26, shoots great and I am considering using that for elk this next fall. I also am planning to try the Berger 175 Elite Hunters this summer, Berger revised their twist rate recommendations and I'm curious whether they'll actually stabilize in my 1:10 barrel or not.
Inside 400 yds, a Partition, Accubond, or Hammer mono would all be great choices.