Beautiful and in such GREAT condition.

Yowser 9 drams is about 245gr. powder.

It's a 13 bore groove to groove - tapered groove depth opf .008" amazing, but standard since the English .58 Enfield Rifles of 1853 onward. Other counties copied this for their military hollow based bullet'd rifles as well, including the US.
27" twist - what weight bullet do you suppose?

What a GREAT RIFLE - well done!