I quit buying Lyman and RCBS molds bullets, years ago, due to dropping undersize bullets. Prefer to purchase from the custom makers. Besides obtaining the specified diameter with a known alloy, can order the exact number of cavities and even opt for PB and GC in the same block. Usually, with a choice of block material. Since, I have pistol/revolver combinations, I almost always order mixed cavities of PB and GC. I own exactly one Lee mold, conical for my ROA. Learned casting 50 years ago, using RCBS two cavity molds, entirely by trial and error.