You are getting some really bad advice about the cylinder throats size . To get a new cylinder is pure " nonsense " If the cylinder throats are too small compared to the barrel size, that's a problem . If they are a little oversize compared to the barrel , that's fine . I have a model 25-5 ( 45 colt) that has cylinder throats that are very large . It is the one of the most accurate revolvers I have . I cast and shoot bullets size .454 instead of .452 .
YOur bullets sized .430 are really at least .001 too small in diameter. YOu mentioned getting some powder coated . That should add enough size to make them acceptable , probably around .431-.4315 .
I am wondering if you have a tight spot in the barrel where the barrel threads onto the frame . This can happen when they " indexed " the front sight to the rear sight . They would of had to over tighten the barrel to get the sights lined up . When you drive a lead slug down the barrel . If you hit " a wall , a tight spot " just before the slug exits the barrel , forcing cone , there is your problem . Make up some " fire lap " bullets to solve that problem . It takes proper internal dimensions to make revolvers fire cast bullets w/o leading the barrel and obtain acceptable accuracy .
Veral Smith @ LBT Molds sells a little soft bound manual describing what it takes (internal dimensions ) to have success shooting cast bullets in revolvers and how to fix the problem areas . It's titled " jacketed performance with cast bullets " . It sells for about $15 , well worth the price .