Let's not derail this marvelous thread, but to answer your question Barry, I have been reluctant to fire the Kavanagh on account of the patches over the pin-fire holes atop each chamber, one of which seems to have ever so slightly loosened. I did get part-way towards making some seriously heavy brass hulls from .50 BMG cases a la Ed Hubbel's early "12ga from Hell" but got side-tracked before turning the rim collars... Another job for a rainy day?
Would have used maybe 2 drams of BP under a round ball just to say I've fired it, then maybe worked up towards 3 drams to investigate regulation, but the plod here are being silly about the discharge of antiques so technically I would have to change its registered status to "shooter" to be on the safe side.