Zonie: My brother bought an old gun several years ago. He thought it might be .36 cal, but the muzzle seemed to be oval, rather than round. When we got home, a .36 cal. rod would not go down the barrel. He eventually had the breechplug pulled, and found a bore obstruction about 5 inches in front of the chamber, which still held some black powder! The bore was so pitted, it had to be rebored and rerifled. It is now .42 caliber. The barrel had been coned, but it also showed wear in the last 1/2 inch from years of ramrod use. The barrel dates to the early 1800's or late 1790's, as best as all the experts who have examined it. He is happy to have restored it to use.
For our purpose, the likelihood of a shooter wearing a muzzle evenly over 30-50 years of shooting and cleaning is remote, if even a possibility. With today's steels, it would take 4 times that long to wear out the muzzle. This old barrel is iron, and much softer. You can see the hammer forging marks on the bottom of the barrel, as only the top 5 flats are draw filed to shape. This barrel was taken from a flintlock long rifle, shortened, and rebreeched, and made into a half stock percussion gun in the 1870's or '80's. We didn't know what coning was, until after the barrel came back from the man who rebored and re-rifled the thing. It shoots very well, although the patent breech has had to be redone on it, since he got it.