Yes, you can use .38 Spl. data to load in .357 Magnum brass, but it will not give the same velocity. If using plated or jacketed bullets the charge should be increased to reduce the chance of a squib and stuck bullet. To get approximatly the same velocity in .357 cases you need to increase the charge weight by not just .1-.2 gr, but 12-15% to get the same velocity. If the charge is, say, 3.6 gr. Bullseye you will get the same velocity with about 4.1 gr. in the larger case.