Great looking rifle.
Great looking group.

Are your sights marked?
Do you have a chronograph?

I've seen quite different regulation velocities between blackpowder and nitro for black loads.
The substantial difference of ejecta mass definitely makes a difference at the chronograph.
Wright's extensive pressure testing at birmingham shows consistently lower pressures with modern NFB loads and at times heavier bullets than the 'old time' black powder loads did.

Still, it is very rewarding to get such a sweet old small bore double rifle shooting so well burning coal!


--Tinker