Any forcing of the ball to follow rifling will increase pressure a bit, even though velocity isn't retarded much if any. We've done tat test using .62 cal rifles and smoothbores wiht black powder - maybe that's why, but it has alwasy been said that smoothbores shot faster- not true all the time. I wouldn't worry at all with your Martini.
; Twist is perfect. I have a .745" mould that Jeff Tanner made for me, and it casts .742" in WW metal, perfect for your bore. Too bad it casts the ball my bro uses in his 1728 Bess.
: Great accuracy - great power - what more could a guy ask for?
; Have you googled express sigths yet? There might be something there that would be perfect.