All, Denver's question on Saeco molds (and my reply) prompted me to ask the above question, which E.H. Harrison himself asked (author of NRA's "Cast Bullets" based on articles appearing in the "American Rifleman" from 1957 - 1979). And yes, I know all .30cal. molds aren't undersized, and other cals. may be too, so let me be more specific. To wit, Lee, Lyman and even Saeco bore-riding designs often cast too small to give optimum results from a standard .30cal., but not .30-30Win. bbl., when cast of WW + 1% Sn, or Lyman #2 (5% Sn). E.g., my Lee C-309-180R, Lyman #311291 & its elongated cousin, #311284 and Saeco RG-4 (now #301) have foreparts that are too small (.299" - .300") and thus, don't ride the bore of my .30-06 (Mod. 70). It's not just confined to .30cal. bbls. since I have a Lyman 95gr. bore rider and RCBS 105gr. SP in .243Win. whose noses are also too small.
Does this condition exist because there"s little agreement on standard bbl. dimensions, e.g., .30cal.; because there's little agreement on what constitutes a standard alloy; because mold manufacturers (not the custom shops) were/are unable to hold close tolerances and sell molds at reasonable prices; because manufacturers (again, not the custom shops) don't set high enough standards for quality control? Have our expectations of CB performance changed so much over the last four decades that we demand better molds with more precise/better fitting CB's? Is it a combination of all of these factors? Inquiring minds want to know!