I concur 100% wth slugging the bore and the cylinder throats. More barrels are fairly easy to measure but Smith & Wesson barrels have five lands and groove so unless one has the special type micrometer to measure the slug from the barrel the best one can do is an educated guess.
Let's say the gun is a .44 magnum and the groove diameter is .429" Also, let's say the throat diameters are all exactly .430".(Not likely but sometimes one gets lucky.) Then I would size the cast bullets at .431".
Where the problem with the throat comes in is if it's too small. Using the numbers above if one of the throats is too small, say .428", loads from that chamber will probably never be accurate and definitely a source of barrel leading. Not good.
I've done the above one just about all the revolvers I've ever owned and it does make a difference. For one thing, the only jacketed ammo I used are in my self defense handguns. For any other purpose I shoot strictly only my own home cast bullets. I've been using cast bullets in my handguns since the middle of August 1954. I run cast in quite a few rifles as well including deer hunting back when money was scarce.
Paul B.
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