When the black powder era ended and the cordite era started, at the end of the 19th century / start of the 20 th century, a number of cartridges that were black powder (BP) cartridges were converted to cordite. As everyone here knows, BP-proofed rifles were changed for cordite-proofed rifles, some BP-proofed rifles were reproofed for cordite, and some BP-proofed rifles were re-barreled for cordite, especially rifles with Damascus steel barrels.
However, cordite was very sensitive to temperature and pressure could spike in Africa, resulting in sticky extraction. This caused issues with cases that were originally designed for BP and that typically had fairly thin walls and rims.
The concept behind the #2 cartridges (.450 #2 and its replacement .475 #2 when .450 caliber ammo was outlawed in India and the Soudan) was to produce massive cases with higher volume, thicker walls, and very much thicker rims that could not be sheared off by extractors. As a consequence of the volume of the case, the ammo operated at lower pressure (13 tons for the .450 #2 instead of 15 .5 tons for the H&H 500/.450, and 17 tons for the Rigby .450 straight case), and as a consequence of walls and rim thickness, extraction was worry free. In terms of performance on game, there was no difference.
To this day, the .450 #2 retains a bit of a cult status (it is for example the favorite cartridge of George Caswell, the owner of Champlin Firearms) but there is no readily available commercial ammo for it, and cases are hard to come by. I owned a .450 #2 in the 1980's, a beautiful Belgian pre-WWII Jules Bury, but ammo procurement was a constant nightmare and George Caswell made me an offer I could not refuse...
