Another important measurement is the diameter of the cylinder throats. If the throats are undersized, the bullet will be swaged down to a diameter smaller than the bore, causing the same problems as undersized bullets.

I have a Ruger GP100 that had undersized throats. I couldn't push a jacketed bullet (.357" diameter) through four out of the six throats. I had a machinist open the throats to .3585 and leading went away. I can shoot 140gr hardcast bullets at 1,200 fps+ with virtually no leading.

Chris