Nice rifle - thanks for posting it.

I think that if the rifling is fast, it is for a long bullet, not an express bullet.

The English EXPRESS rifles have slower twists as the bullets were light weight for the caliber and were driven by rather large powder charges for the bore size, hence the term - "express" meaning high velocities.

Slow moving long bullets required faster twists, hence the faster twists in rifles designed for long bullets.

Typically, a .40 calibre rifle for a short bullet and fairly large powder charge would have a rifling twist in the 30" to 40" range, such as a 240gr. to a 260gr. bullet.
A .40 calibre rifle for a long bullet, would have a rifling twist in the 16" to 20" range for shooting bullets from about 360gr. to 400gr.

A .45 would run 30" to 48" in slow twists for short bullets, while a .45 would have from an 18" to 22" twist for longer bullets.

It is an interesting rifle & sight, with the weight of the barrel (thickness) telling me it was meant for a heavier bullet.

A 10.25X69mm ctg. would hold between 70 and 80gr. of black powder with a 360gr. to 400gr. bullet. It would be very similar to the .40/70 Sharps bottle necked ctg., I believe.

The ctg.would be quite suitable for any of the antelope and perhaps probably for the cats.

The various .40 calibre Sharps ctgs. were favoured by many hide & meat hunters for the shooting of bison on the American plains. Most used the 370gr. PP bullet.