If you're going to rebarrel a rifle, it's important that you mark the caliber for safety as well as legal reasons.
Hold the barrel tight in a heavy padded vise and mark the caliber. Use a straight edge and mark just above the centerline. Double-check the stamp and place it next to the guideline, then hit it sharply. One strike and one strike only with a ball pein hammer.
Continue stamping one number at a time. If the number isn't well-struck, reposition the stamp and strike it again. The raised edges around each number will need to be dressed down.
Start by using a fine file, and follow it up with some abrasive paper.
Well, now we're safe and legal.
-- Larry Potterfield