Hi, I came across this discussion (and your confession) by chance, and it made me register for this forum.
Congratulations on the rifle. I have about the same (as well as an almost identical by Webley & Son). Yours is however in original condition with the retracting strikers as patented by Greener in 1868 (patent no. 800, March 7.1868) W.W. Greener didnt like striker springs (nor rebounding locks ..). He described this rifle in Modern Breechloaders page 100 and following pages. He suggests an 11-bore round ball or a hollow point or massive- conical bullet (same as for Paradox).
The right-hand twist of the 11 lands will probably something like 1: 4ft 5, the grooves being approx. 0,08deep.
Youll probably find Sighted with 4 Drams of Powder on the action. I assume this goes for the 11-bore ball as mentioned by Greener. Castbulletengeneering in Australia can supply you with moulds for both round ball and 12-bore Paradox. Brass must be available in the States. I use 4 dram (7 gram, were in France !) Swiss BP nr 3 (2FG) + some wads and a bit of grease. Shoots well with both round ball and conical HP, but round ball requires quite a bit of crimp to keep it tight on the wads (probably because I use 12-bore ball (round ball .695).
It will probably be a bit difficult to get provenance from Mr Graham Greener since the books of this period (abt 1868 or slightly later) seem to be lost.
I hope I may contact you in the future for a close-up pic of the hammers for an article Im writing on these rifles.