This is my take and experience on slugging bores. For the most part, it is a useless effort. You can pretty much determine the actual caliber of the bore with a simple dial or digital vernier caliper at the muzzle. Several things contribute to inaccuracy of the actual slug you push out of the bore. Uneven wear throughout the length of the bore. A constricted area under the barrel threads. (In revolvers). Or any constricted area along the bore. You will have a slug that measures the "constriction" and not the actual bore. Lead or copper build-up. Straightness of the barrel. Etc., Etc. Depending on the alloy of the lead slug, you may get expansion after the slug leaves the bore. When measuring the slug, if the caliper arms press into the lead, you will get eroneous measurements. Actual bullets fired can and will act entirely different when pushed through the bore under firing pressure. Casting a chamber to determine cartridge caliber is a completely different proposition and is very useful. In an old firearm with a bore that is pretty well worn, slugging the bore and casting the chamber can be a useful endeavor in determinig just what you have in your hands! Slugging the bore on a newer firarm is not going to give you much useful info if any that you don't already have. Others may have a "different" experience than mine!..........................Dick :wink:
