Definately don't recut the forcing cone on modern revolvers, as they are already far too large. Fire lapping will smooth up any part which the bullet hits when not obturated. However, under full magnum pressure, bullets do swell out into the forcing cone, and will be dragging against some roughness, but I believe it is better to keep the forcing cone small as possible to minimize obturation here. Though most of the obturation control is mandated by alloy hardness.
Soft cast bullets under magnum pressure can swell out into the huge modern forcing cones with enough force to crack the barrel/frame.