I'm going to assume that you're talking about cast bullets. Jacketed bullets should be loaded and shot as they come from the box. No sizing is necessary.
Your revolver should have a chamber mouth that is 0.001 larger than your forcing cone and the bullet should be sized .001 larger than the chamber mouth, assuming that you're shooting cast bullets.
What you're looking for is for the bullet to hit the chamber mouth and be properly sized to enter the forcing cone. A revolver with tight chamber mouths will have the bullet improperly sized when it hits the forcing cone and you'll get excessive leading and poor accuracy. With cast bullets, size is everything.