Them breech plugs are for the old .45 & .58 caliber "H&R" Huntsmans. I don't think he is making any breech plugs for the .50 caliber "NEF" Huntsmans, at least not the last time I talked to him a couple years ago. He did say he ought to get one of the newer Huntsmans and make plugs, but I don't think it got any further than that as far as I know.
I bought the .25 ACP plug and haven't looked back. The 209 is a messy pain in the rear compared to the .25 ACP.