Actually, if you scale up that 10.3 gr. .177 cal JSB Heavy using the cube of the bore, you get a pellet that looks exactly the same.... The weights would be.... 54 gr. in .308 cal.... 85 gr. in .357 cal.... and 177 gr. in .457 cal.... There is a 78 gr. EunJin pellet in .357 cal (9mm) which is close.... Scaling pellets directly is possible, it just doesn't seem to be commonly done....

Bob