Peter-

What's the barrel length?
That's ten pounds no ounces?
What is the rifling profile?
What do the sights look like?

My initial thought is four or four and a half drams and spherical ball, but that's off-the-cuff without knowing the chamber length or barrel length. It appears to be a light sporting rifle to me, not so much the elephant killer.
Note the narrow breech, very open grip, thin wrist, and not excessively long action bar.

Cheers
Tinker