Howdy!
Me too, I always loved this cartridge. I remember my grandfather, he told me about this rifle that was firing at five kilometers, as it was written in the dictionary.
I shot several boars with my Berthier mousqueton, it have a pretty tight bore, so I used RWS 323" bullets with nice accuracy.
I owned lots of 8mm Lebel rifles or mousquetons, and bores range in size from 325" to 330". I slugged this Rival, and I found .333"!
I haven't shot it yet. But I think to size down 338" bullets to 334". I already did it for my 10,75X68. A cartridge loaded with Hornady Interlock 250 grains round nose would look good!

A Lebel rifle is no laughting matter. I own one with superb bore (very scarce thing), and regularly I beat shooters firing much more modern guns, with Lothar barrels...
I use Prvi brass, but Tpm bullets, they're astonishing.

Until 1939 everything was free, from pistols to machineguns. I don't know in colonies, but I had a friend who made meat in the 50's with a 1907-15 rifle, so it was probably free.