The gauges are next to worthless and not needed. You just want to break the inside leading edge as well as clean up the forcing cone. You can tell this by feel. If you have never done this then perhaps you need someone to show you how to do it. I've done my own for years and it's difficult to overdo it, however you're not trying to make a blunderbuss. Remember to use a good cutting oil and to back out the tool IN REVERSE now & then if it seems to be chattering, i.e., overloading with chips. After you have gone far enough to remove the roughness then without cutting deeper merely turn the tool lightly to burnish the cut somewhat.


There is another solution for barrel/frame constriction that is called Taylor throating. Some do not subscribe to it, however I have seen it work miracles on some guns.