I don't have any personal experience with the kind of load you're looking for, but I note that the Speer (#14) Reloading Manual lists some reduced loads for the 280. For example, it lists 21.0 grs of SR 4759 with the 145 grain bullet for a muzzle velocity of 1689 ft/sec out of their 24" test barrel.
Good luck in your quest.
Good luck in your quest.