A rifle listed as 400/450 turned out to be 3 1/4 rather than 3" despite not saying that anywhere in the ad. I discovered it by enlarging the pic of the barrel and seeing that inscribed. So that got me wondering...does 470 NE rifles have any variations or are they pretty much standard though the years? IOW, would I expect a 470 made in - say 1920 - to originally have the relevant chamber/barrel specs as a modern one/be able to shoot modern .470 ammunition?
@MexicoMike
You're asking a thoughtful question, but you need more context on double rifles to understand the underlying gotchas.
First, was metallurgy better in 1920 or today? Generally, metallurgy is way better now.
Second, vintage British doubles were underbuilt, its why they are so coveted. They struck down the barrels, keeping them thin and lively, rather than overbuilding things that make them needlessly heavy or poor handling.
The British double rifles were wholly acceptable for the original 1921 and 1926 ICI / Kynoch load pressures based on stranded cordite.
Third, unfortunately, the expert ballisticians at Hornady, Federal, and elsewhere don't know the first thing about double rifles. They do know that for general accuracy, optimal accuracy is typically found by filling a case to capacity. Not filling a case to capacity can cause a double fire and dangerous conditions. For these reasons of mass production and ignorance, the modern loads use HORRIBLE powders that fill the case. They also change their bullets and load recipes with an unfortunate frequency which means your double rifle is worthless and unshootable when they change the load that your new rifle was designed to shoot. Just assume that you MUST have a custom regulating load built for your rifle to ensure it will function forever, rather than holding to the delusion that the factory round will be in stock and exactly the correct one your rifle was regulated for at the factory.
Fourth, remember your question about modern loads versus original loads? The ballisticians that make factory loads have made another error due to ignorance. They believe as long as they can make the ammo shoot to a given pressure an a given FPS, it should be fine. It would be fine in a modern bolt gun, but not so in a double rifle. The original guns were proven safe with an original load that had an ORIGINAL PRESSURE CURVE. Modern powders that fill the cases are not similar to the ORIGINAL PRESSURE CURVE even if the velocity is identical and the pressure is identical. Powder burn rates matter.
So what's the solution? Whether you have a modern double or a vintage British double, you get a hand load developed that reproduces the cordite pressure curve. Thus, you've duplicated original safe operating parameters. These powders won't fill the case, but a wad or stuffing keeps the powder pressed against the primer totally alleviating the need for powders that fill the case. The best part? A modern Federal 470NE load puts out 89lbs of recoil using 106gr of 4831 powder. The same rifle using IMR3031 puts out around 58lbs of recoil.
In Conclusion: buy a modern double rifle used, or buy a vintage British double rifle, but in either case only buy one that comes with regulating targets and load data that demonstrably proves safety and accuracy. OR, take the risk and uncertainty of buying one and building your own regulating loads, but caveat emptor in that case.
