Wow! For having over 1200 posts on the Ruger Forum, I would think you would know what a revolver forcing cone is and what they look like.
So... That part of the barrel is known as the forcing cone. Every revolver needs one. It starts out with a larger diameter than the bullet, and tapers down to the bore, where the rifling starts. It is supposed to be smooth (unrifled). It allows for the bullet to smoothly transition between the cylinder chamber mouth and the barrel bore, even when they are slightly misaligned.
A gunsmith may use any number of implements to remove metal on a gun. I have no idea what specific tool/tools were used to work on that part of your gun. If you posted some photos of the area on the gun, some of us here on the forum could provide our educated guesses on the possible tool/tools that were used.