Pvanwyk, I have a rifle that I believe to be identical to yours. (Pedersoli Mortimer Whitworth). The barrel bore is rifled, not hexagonal, though. It's still unfired, partly because I don't have any loading data for it. I bought it from a store that was closing, and took it as is. It is beautifully made.
I would appreciate your loading info and/or anyone else who knows this rifle.
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time