sambarhntr,
Are you shooting the 4 shots without any chance for the barrel too cool? I don't believe barrels ALWAYS need to be cooled between shots, because have run into too many that don't, including some lever-actions with 2-piece stocks and a band around the forend. But often 3 shots is about the limit for BLR's before allowing them to cool.
Do the group sizes you list include the "fliers"? If not, then the accuracy should be more than good enough for big game with the .358, which isn't exactly a long-range cartridge.
You might get better accuracy with some dinking with the forend bedding, or other powders and bullets. You might even get better results with magnum primers and 748.
