I agree with Pavo here, BUT would like to point out that the critical measurement that the bullet must be sized for is the diameter of the chamber throats in the cylinder, rather than the groove diameter of the barrel (which is also important). The bullets need to be .001" or .002" over the throat diameter, AND while the diameter of the throats should equal or SLIGHTLY exceedthe barrel's groove diameter, they should be no larger than .002" or perhaps .003" over groove.The reason for this is that upon emerging from the cartridge case,the bullets will swage up to fill the throat. When they hit the forcing cone, they will be squeezedback down to fit the groove diameter of the barrel. If the bullets are forced to swage down too much by the forcing cone/barrel, they will be deformed and can enter the barrel crooked. This effect SURE destroys accuracy.

You can pretty much predict how well a revolver will shoot by measuring chamber throat and barrel groove diameters. If a cylinder has chamber throatsrunning under to just a couple thouandths over barrel groove, it will usually shoot well, or can be made to shoot well by lapping the chamber throats to a larger size. IF the throats are alot bigger, a new cylinder is called for.

I once owned a beautiful Colt New Frontier in .45 Colt. The groove diameter of the barrel was .451". But the cylinder's chamber throats were .456". This gun never shot wel with any sort of cast bullets, hard, soft, etc., regardless of bullet sizing. It was just barelymediocre with jacketed bullets. Had to ditch the thing!