In a perfect world, a revolver's bullet is sized .001" to .002" greater than groove diameter, cylinder throats are sized .0005" to .001" greater than bullet diameter. This arrangement works in all calibers and all makes, cast or jacketed.
If you use a reamer, the single most important factor is getting a pilot that fits VERY snugly in the old throat. Many Ruger cylinders are quite inconsistent due to their manufacturing process, i.e. they replace reamers as they wear so some cylinders have a pair of larger throats cut with a recently replaced reamer, and the rest cut with older reamers that cut smaller and smaller as they wear.
And then there is the extreme variations in hardness from not only cylinder to cylinder but in the same cylinder it is pretty common to see one side of the cylinder with 2-3 throats that cut like butter and the rest of them you think you are going to twist the shank off the reamer. These cylinders will always finish with inconsistent throats because the reamer will cut a larger diameter in softer steel than it cuts in harder steel. For these reasons, I switched over to using a Sunnen precision automotive hone to overcome the inconsistencies in the metal itself.
Sometimes cylinders come in with really badly egged holes and I have to use the Sunnen hone to true them up IF I want to follow with a reamer, The Sunnen does a wonderful job at cleaning up behind the reamer but it by itself is not a boring mill and I try to stay away from taking more than .002" out of throats with it. Those jobs are better done with a reamer then followed by the hone.
There is actually a lot more to correcting cylinder throats than one would think. It seems simple and straightforward. It is not. You may get lucky in reaming a few cylinders, you may not get lucky and your first one goes awry because of the aforementioned variations in hardness. It's totally speculation until you put the reamer to the steel and start cutting. Only then will you know how the job will go.
