I have found and read "450 Nitro History" by Wieland, and I have a few questions, so I can gather some knowledge.

In the early days, did the 450 Nitro, 3 1/4" go by any other names? Wieland indicates that they were at first just another 450, or 450 express.

On the web, I see a WR for sale as a 450 HV, but scratching around it appears to be a nitro proved rifle. Also a Purdy 450 Express that is supposed to be a 450 NE. And last a Rigby Hammer Underlever, as "Special cordite Cartridge 480 grains". The Rigby is safe to me since it is claimed to be lettered as a Nitro Express, and has been refurbished and re-proofed. The others?

So are these just name changes, or should one try to research them through the makers? Has the 450 NE always been proofed as 70 Cordite and 480 grains, or did this come after 1900? Would a picture of the proof marks have enough information?

Thanks for the help.

According to the "1954 Rules, Regulations and Scales by GUNMAKERS' COMPANY and the GUARDIANS OF THE BIRMINGHAM PROOF HOUSE" book, the proof loads for the .450 NE and the .450 Nitro Express No. 2 are as follows:

.450 Nitro Express--87 grns Cordite, 480 grns bullet with greased cloth.
.450 Nitro Express No. 2--93 grns Cordite, 480 grns bullet with greased cloth.

The 450 3 1/4 and the 500/450 were the most common black powder rounds. They would have been known as just a 450 and many were marked as such on the barrel flats.

In some cases the only way to tell the difference between the two is to cast the chamber.

The "express" moniker came about by Purdeys to indicate a lighter than normal bullet weight, thus a faster round, in the blackpowder era.

Rigbys developed the 450 3 1/4 nitro approximately 1898 and rifles prooved for that round would typically be marked "70 cordite 480 gr".

It's common to see early Rigbys not prooved for the nitro round but to be marked on the barrels for the nitro round. Based on the barrel markings and the weight of the rifles you would certainly believe they were built for the nitro round. I've never heard a good explanation to explain this.

I never had much interest in a BP rifle later reproved for a nitro round.

The 450NE indeed was a development of Rigby's and early on they offered two bullet weights, 480gr and 365gr. From my reading, the 480gr load was quickly standardized, my assumption is that the lighter bullet is what became the "Light Cordite" load for black powder proofed rifles. I am unsure if the original 365gr version had a lighter charge or not.

It is often overlooked that most of the 450 class cartridges were offered in more than one charge/bullet combination which was really a holdover from the BP era. The 450 BPE being a classic example offering many different weights with the more or less standard charge of 120grs black powder and the 461 No.2 Gibbs being another with the actual sights on their rifles often filed for both 570 and 360gr bullet weights.

In fact most modern day buyers of classic nitro double rifles never consider using lighter bullets other than when applying the 75% rule which is generally thought of as a modern adaptation for loading and regulating doubles.
The truth is, this 75% rule was in practice by rifle makers way back when they were being built.
The famous advertisement by Holland and Holland showing seven shots from their 465NE rifle covering the space of a postage stamp was produced using 365gr bullets not the 480gr bullets. That's a pretty good example of the 75% rule right there. The earlier H&H 500/450NE was offered with bullet weights of 480, 420 and 370grs as well.

Not sure but maybe some help. DGJ vol 6 issue 4 has an article by Ross Siegfried about an WR "Long Range" marked double that may shed some light on OP question re. HV marking.