I have a 280 Remington with a 26 inch barrel.
I have been trying H4831sc with 59 grains max load and getting about 3,070 fps with a 140 grain ballistic tip. The accuracy is excellent but I am wondering if anyone has gone hotter than this? Also, are there any other powders that could work better? I've been thinking about Reloader 22.

PrimeTime,
In my opinion you are about 1 powder level too slow with the H4831sc. The RE-22 is even just a pinch slower than that, we use it in the .300 Ultra Mag. not a case the size of the .280 Rem.
I ran some preliminary numbers through the computer and came up with either IMR4350/H4350, H414, W760 and Norma 204. But the best according to theory is V V N550 which gets about 150 fps. more than the others at the same pressures.
Just some thoughts.
Bill

My Rem 700 in .280 has a 26", #3 taper Douglas and those extra few inches seem to help the velocity a bit. I have done real well with either Reloader 19, or IMR-4831. My sort of "universal" .280 load is a 150 partition, RP case, 56.0 of IMR4831, WLR primer, for an average of 3050 fps with about .8" accuracy at 100 yds and 1.5" at 200 yds when I have a good day.
IMR4350 gave me very good accuracy but with a about 200 fps less velocity with near max loads.
With heavier bullets, specifically the 175 grain partitions, IMR7828 has given very good accuracy with decent, though not earthshaking velocity. 57.0 grains yields an average of 2875, but VERY accurate.
Great cartridge the .280 Rem, one of my favorites.
FN

PrimeTime -- I think the advice you received about H4831 being just a tad on the fast side with 140 grainers is right on. I use RL-22, a really full case, behind Sierra's 140 gr. GameKing for just a little under 3100 fps out of the 22" barrel of my Browning Medallion.

Whether the velocity were 2900 or 3100 fps doesn't matter all that much to me, but this just happens to also be one of the most accurate loads I've found. Although I have not pressure tested this load, I am quite sure it is operating in the 65,000 psi pressure range of the 270 Winchester.

I have something simular, a 7x 64. My deer load is 55gr IMR4350 with a 150 nosler BT. It is very accurate with a velocity of 2874. Could prob go higher, but i load for accuracy. Oh its in a 24" barrel CZ550

Prime Time
I just started playing around with a .280 Rem.(26" Heavy tgt.BBl.,1-9 Twist), Started with Rem.Case 55 Grs.R-19,150 Grn,Matchkings and 150 Nosler BTs., Intrestingly enough the 150 BTs shot tighter groups at 200,than the Matchkings,Both were extreamly accurate. I have not checked speed yet but required 12.75
minutes of elevation above 200 yard zero to be zeroed at 600.(2850-2900 fps ???)
I next tried 150 Matchkings with 57.5 Grns. of R-22 in same case, also with good accuracy and appearently low pressure, This load shot 2 minutes Higher at 600 yards than the R-19 load above at same sight setting.
Last load tried was 162 A-Max, with Win.(nick.)case(about 15 grns. lighter than Rem.) with 56 Grns.R-22, This shot extremly accurate at 600 also,and was dead on for elevation,as the second load (150 & 57.5,R-22)mentioned above at the same sight setting.
Not looking for Warp speed here, just a good 600 yard target load .
Hope this helps.
Charlie S.