I agree with the Brownell's recommendation. They have a great tech line. I have been dealing with them for over 30 years now and have yet to be diappointed. Cerrosafe is the way to go with chamber castings. I cast the chamber of a Remington Rolling block rifle in the early 70's with it and the dimensions were what told me it had a .43 Spanish chamber instead of the .43 Reformondo, which is what the company who sold the rifle to me had told me. Good thing too, if the .43 reformondo had chambered and I had fired the thing, it would most likely have blown up in my face. Wish I had kept that little package of cerrosafe, but I gave it away to someone. James