Back "in the day" the .450/.400 3 1/4" BPE was a calibre suitable for Deer stalking, Tiger, Blackbuck, or other smaller thin skin game that was not so tenacious of life.
The BP loading was “usually” a 230 grain HP bullet at claimed 2000’/sec or a 255-270-300 grain solid lead bullet at somewhat slower.
Hardly the horsepower to handle the Asian Gaur, Water Buffalo, or other large bovine……the existing writings indicate that the old boys would have used the .577 Express (or 12 bore) for that.

The C&H Certus was chambered in the .450/.400 3 1/4" Nitro Express (400 grain bullet at ~1950-2000’/sec), a totally different power category.

That Lyon & Lyon is a very nice looker…..if the bores and chambers are in good shape it would be great fun.
- Mike