Thanks Ben,
Both would likely have originally gone to, or been intended for India.
The Rigby has a faint 3 digit "Maharaja number" behind the pistol grip.

The Scott shows very little wear and perfect bores/rifling so was probably caught up in the India/Sudan ban on .450's and fired little if at all from ~1899 to the ban. Thereafter maybe just languished in a cabinet because hammer rifles and the .500/.450 3 1/4" had become dated and out of fashion?
I have found that neck expanded and fireformed .500/.416 brass are the easiest and least expensive way to get this .500/.450 shooting.

The Rigby's buyer, J.T. Hartwell, traded as a "Gun and Rifle Maker" at 5a West Chapel Street then all of 5 West Chapel Street, London from 1919 to 1925, the Jones Underlever and hammers on the Rigby are pretty unusual for as late as 1919.
- Mike