I have a bunch of that and a bunch of musket caps... Although I have a breech plug around here for musket caps that will fit the G series because I believe most White breech plugs are interchangeable. When I purchased my Model 97 Ultra Mag it came with breech plugs for 209, musket, and #11 caps. All I have ever used were the #11 caps as I never had an ignition problem using a good #11 cap and there is not so much blow back with it.