Data from the Guns and ammo August 06 by Chub Eastman.
Hornady IB 139gr, imr4350 57grains, fed210m, 3,078fps, 53,700CP
Nosler BT 140gr, ARel 19 60 grains, fed210m 3,054fps, 52,000CP
Swift Scirocco II 150 gr, H4831sc 60 gr., WinLR, 3,053 fps, 59,000CP
Nosler AB 160 gr, AA3100 58 grains, Fed210m, 2,845 fps, 53,900CP
I usually start with the max loads listed for the 280 rem, and work up shooting over the crono and checking for pressure signs. If you meet or start exceeding speeds of the 7mm rem mag you would be very wise to back off!
I have found H4350 to be a little too fast for my 280ai. If you don't mind using Alliant powders Reloeder 22 works very well. I have also had good results with H4831sc and H1000 with heavy bullets.
Hope this helps.