RE: .257 Roberts?
bige1769,
Try 46.5 grains of IMR 4350 with an overall length of 2.78 inches (tip to base) that will give you about 3000 fps and is near maximum so work up to it. For IMR 4895 you will give up some velocity (50 to 100 fps) but you may get more accuracy using 39.4 grains at the same length.
SAFETY NOTE: always check any loads you get from any source with up-to-date loading manuals before using them. Always start low and work up gradually to find your most accurate load. If you don't find accuracy before reaching LISTED MAXIMUM LOADS then change to a different powder and begin again. NEVER exceed maximum listed loads in the latest manuals and always check multiple manuals for accurate data - errors do occur!
PaulS