As I truly appreciate the originals in original condition it does pain me to know of this practice.

About 40 years ago I bought a Rigby boxlock DR that had been brought out of India by John Roberts & Son. Restored and rechambered by them to 9.3x74 it was a nice rifle. The fired brass did have a weird looking shoulder……
Would I like to see this mod done today? No, especially as I go to the effort to handload for all the obsolete cartidges in those rifles that I have.

Several thoughts come to mind here:
1) not every Brit rifle shooter is a handloader, thus those guys depend upon available factory or custom loaded ammo.
2) for decades the various .360 ammo was simply very scarce old ammo or completely unavailable.
3) sometimes not even brass suitable for conversion is available.

These days I personally dislike the conversion to 9.3x74 except when the bores on the original rifle are too far gone to be usable.
It IS possible to find components and dies for the .360’s these days, so why alter a fine original.
If one is not a handloader then they ought to learn……..
- Mike