[mrerick]

Don't forget that 9mm Luger headspaces on the case mouth. Upon insertion into the chamber, it stops when the mouth reaches the correct depth against a shoulder step in the chamber.

If you taper too much, it might either miss the shoulder or cant against it at a slight angle if the chamber is cut loose.

This is one reason I don't overwork the mouth of a 9mm case by "belling" it large for bullet insertion. Just a slight amount is enough to center the bullet to be pressed in properly.