ЕЕЕ.. back to Nitro John's original question: "Early Big Bore Bolt Action Rifles"

There was the Cogswell and Harrison "CERTUS" which was, via updated patent in 1900, offered in the large cordite Nitro Express cartridges.
Their 1903 catalog advertises .450/.400 3 1/4", .450 3 1/4", and .450 No.2 3 1/2".
The .450/.400 and .450 NE cartridges were both offered in special proprietary "CERTUS RIFLES" loadings. The .400 loads with what amounted to "tropical" loads of Cordite and, in the case of the .450, a 440 grain bullet vs the usual .450 NE 480 grain bullet.
The .450 No.2 was, due to its size, a single shot but none the less was a bolt action.

Have not seen mention of any surviving .450 No.2, but there are (mine included) a few .400's and .450's to be found.

The CERTUS is/was certainly an odd duck (tho it worked) and was only marketed for a few years.
IMO once Rigby introduced the Magnum Mauser action it was all over for the very unique C&H CERTUS.
- Mike

ADDED: not to denigrate Winchester rifles and their .45 and .50 cartridge offerings, but the original factory loadings of such were simply not in the same league as the big Cordite Nitro Express cartridges.
The afore touted .45-90 2.4" cartridge was originally loaded with 300-330 grain bullets at about 1550'/sec with a slow 1:32 twist and could not stabilize 450-500 grain bullets. There was a 450 grain loading for rifles with a faster twist, still limited to black powder velocities. Later on there was a "High Velocity" .45-90 300 grain bullet smokeless load at ~1970'/sec which would basically duplicate the old .450 3 1/4" Express "Nitro for Black" loadings.