In my limited experience, I have found a good starting point is to size the bullets (or purchase) to the same size as the cylinder throats. Ninety-nine percent of modern manufactured revolvers will have cylinder throat diameter larger than groove diameter, but don't assume anything, slug the barrel and measure the groove diameter (the larger diameter of the slug). You can also get accurate measurements by slugging the cylinder throats, but I prefer pin gauges too. I prefer softer bullets, 12-14 BHN, in my 5, .44 magnums and 3, 38/357 Magnums, and I'm able to shoot them nearly leading free. I have gotten 1300+ fps with a .357 Mag. LSWC, plain based, air cooled, Speed Green lubed bullet from a 4" revolver. A slight overload of Trueblue from a moment of distraction (only made 12 rounds)...