I have an antique 1886 in .45-70 coming. It was made in the 1880's, and went back to Winchester in 1921 for a new barrel. I don't have any experience with these, don't know what Winchester had for chamber specs like throat diameter and freebore.
I'm going to slug it when it arrives, so I'll have the groove diameter, but I don't have any cerrosafe to make a chamber mold.
Any advice is appreciated.