You are saying each firearm has different standards for bullet sizing after the bore size is determined?
I agree, lead bullet are standard diameter same as jacketed. Basic is .001" larger than jacketed for handguns. 45acp=.452" 38 special=.358" 44mag=.430" One exception its 45colt, new guns=.452" Old Colt single actions=.454" Rifles will run on the larger side by .002" 308= .310" But never hurts to slug a barrel. Mr. Lee said >I think we're making it complicated too quickly
Mr. lyman said>Cast bullets size specification
Standard practice is to size cast bullets .001 inch over jacketed diameter, but there is not 100% agreement on this. Some of the sources state that cast bullets should be sized to groove diameter, others state they should be sized to chamber throat diameter, still others state to size to .001 inch under the inside diameter of the case mouth of a fired case. Take your pick...
Plus have your barrel lightly oiled.Q: How do I slug my barrel?
A: Slugging is done by driving a soft pure lead slug through the barrel and measuring the raised grooves present on the slug. A lead round ball used for muzzle loading that is slightly larger than your caliber can be used for this.