H4831sc will work just fine since you have it. Depends on the rifle, some are having really good results with H4350, also. Although I never shot any 140 Amax I had good results with 140 and 142 SMK's and 140 Berger VLD's using necked up Lapua .243's and the Rem .260 brass when it came out. Depending on brass make, charge weights from 42.8 to 45.0 did well.
Shooting in F Class Open, the .260 and 140 class bullets got me to Master in Long Range and High Master in Mid Range, so the accuracy is there and well documented in numerous posts here on the hide by others, as well.
You have what you need to get started - your 26" 8 twist should be just fine.
Paul