I take it that you are talking about the the 264 Winchester Mag.. I just recently purchased the Hornady 8th edition loading manual and that manual gives a number of loads for the 264 with a 140 SST bullets. It shows four different powders that produce 3000ft/sec starting with IMR-4350 and IMR-4831 then IMR-7828 and A8700. I will give you the starting and max for the the IMR powders.
IMR-4350 Start Max
47.3 ------ 55.9
IMR-4831 49.4------ 57.5
IMR-7828 53.3-------- 61.8
With all three the starting load produces 2600 ft/sec and the max load shows 3000 ft/sec. If I were loading this round I would reduce the max by 10% and then work up. I hope this helps.