The breech plug is removable. Ruger had two types of breech plugs, #11 and musket cap. A 209 conversion was available through Cabelas and was made in Canada. Cabela's catalog no longer carries them. I don't have the name handy but I saw the 209 conversion manufacturer selling them on one of the auction sites.
Ah, found it. The original manufacturer for the 209 conversion kit is Armurier Lavaltrie Inc. I don't see them selling them at this time on GunBroker.
