I too have a Black Diamond and on the breach plug and nipple, I use a copper based anti-seiz, that you can buy from most plumbing supply house and will last you forever. I have also used a nickle base higher temp anti-siez but the copper works better for me. The auto supply houses also carry an anti-siez that is primarily used for speark plugs and that will work as well. Then there is the TC products that is rated for this as well as shotgun choke tubes. To answer your last question, I would not use bore butter for this application and I am a fan of bore butter. Bore butter will just not stand up to heat. By the way, If you ever have a need for some 209 primer nipples, I have more than I will ever use as I am currently using musket primers.
Be Safe !!!