All good questions and answers above so I'll leave them posted, with this statement.
FA has always made tight cylinder throats and barrels considerably larger. If they are shot as is, loads stout enough to obturate bullets for a tight barrel fit are mandatory to prevent leading, and accuracy is amazingly good, because they line bore their cylinders, which means the bullets get started straight.
Everyone who has opened up the throats so bullets at barrel groove diameter or slightly larger could be shot has reported a substantial accuracy improvement, with groups under an inch very common, at 100 yards, 2 to 3 inches at 100 yards with the small cylinder throats.
When opening up FA cylinder throats, use some caution that the fatter bullet ammo will not be too large for the chambers, as chambers are held to much tighter tolerances than other gun makers. The tight chambers is another very important factor in FA accuracy, as they don't let the back of the bullet tip.
In other brands of revolvers, chambers tend to be much looser, so opening up cylinder throats, where barrels dictate it, helps reduce the amount of bullet base tip on takeoff. Bear this in mind when adjusting diameters of revolvers. If chambers are very loose, it may be best to shoot bullets considerably larger than the .001 over groove which I spell out as a standard recommendation. The barrel cannot straighten out a cocked bullet, but it can size them down without hurting accuracy too much.
If one could set up a revolver with perfect dimensions it would go like this.
1. The barrel would be fire lapped after installation until groove diameter is tightest out at the muzzle.
2. Optimum cylinder throat diameter would be .0005 over groove diameter at the rifling origin.
3. Cylinder throat diameter would provide a close slip fit for the bullets.
4. Chambers would be just large enough to allow drop in chambering with a clink against the ctg rim, with the gun and ammo clean. Which means after a bit of shooting rounds would have to be pushed in with very slight resistance. This close a fit can cause misfires when the gun is dirty if chambering resistence is great enough to hold ctgs back against the breech so that firing pin force is softened too much to pop the cap.
Of coarse we have to work backwards to fit a production revolver properly, or even to build an all new gun. I spelled the above out so shooters understand the principles for optimum accuracy, not because it can be done in that order.
