With cast bullets the chamber diameter is what will limit your bullet size. For example I load for 2 different .380's one has a barrel diameter of .355" and the other .3573". The chamber on the smaller barrel is large enough to allow me to chamber a round that's loaded with a .358" diameter bullet, so I just size all of my bullets at .358". I used to size them at .356" and they worked fine, but I had to make sure that I didn't shoot them in the gun with the larger diameter bore or it would lead the barrel. Lead easily compresses in a tight bore, you could never come close to the amount of resistance that's created by a copper jacket. I'd measure all three barrel diameters and buy bullets that are .001" larger than the largest bore.