Interesting that I just ran across this 2010 post as I recently acquired an 1872 Rigby .450 Express that is almost a clone of the .500 that started the thread.
I have trouble making out the exact serial number on kuduae’s rifle (135??) but it looks like mine #13856 is about 300 or so numbers higher.

A very close match as to interior action bar details, action face, Jones underlever, fences and top tang....... hammer style is a bit different as they are the flat cut type, mine also has Stanton back action non-rebounding locks but of a “bar action” appearance with exterior action profile to match.
The barrel rib file cut is now mostly smooth, however the script John Rigby & Co. Dublin & London is very well preserved.

An interesting point is that my rifle also has no visible proof marks save for one faint stamping on the left barrel ahead of the flats that looks like a possible London Provisional mark.....that’s it, nothing more.
The watertable and barrel flats have perfectly defined Rigby trademark and serial number stampings.

The steel barrels with very good/excellent bores are Rigby’s style of 8 groove shallow Metford type rifling suited for paper patch bullets. Bore measures out to approximately .454”-.455”with no taper to the bore, and groove measures ~.465”.
Chambered for the .450 3-1/4” Express.

Rifle weighs 9lbs 3oz with 26” barrels and has an older very nicely done barrel reblack and stock refinish with the checkering having been refreshed. Both buttstock and forend are original to the rifle and serial numbered. The case colors may have been redone, but if so it was a long time ago and likely in England from the looks of them. The engraving remains as well defined and sharp as the day it was cut.

Rigby has the records for this one and I am awaiting the information. More photos at a later date.
- Mike