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 .

Replacing the cylinder is not "pure nonsense", if you don't cast your own bullets or are not able to buy a bullet to fit. Casting guys want to bring Mohammed to the Mountain, fit the bullet to the gun. Otherwise the gun is WRONG if it won't fit standard size bullets. Reaming cylinders is routine in order to use lead bullets, but a cylinder with oversize throats requires a complete reset. I have a 45 Convertible for which nothing worked until I bought hard-to-find .454 bullets. Still with a slug size of .451, the gun is a misfit. Ruger wasn't helpful about the question of replacing the cylinder with one of a more current size, typically .451, which I could have reamed to .4525.

FWIW, this thread confirms my 44 Special loading experience exactly.
My most accurate 44 Spl. is the 696. (.430")
Least accurate are the 624s 3", 4" 6.5" (.433")
Also a very accurate Dan Dwyer conversion 5" 28-2 (.430")

Had Penn make up 2000 .432" of a bullet he was discontinuing.
As those were used up. I sold off the 3" and 6.5" 624s.

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-jwk-
US Army '72-'95