Can you use .300 Win, .300 Weatherby and .300 Ultra Mag cartridges in one and the same gun?

No, under no circumstances. Every cartridge has its own designation. In this case, the number 300 stands for the calibre, i.e. 0.3 inches = 7.62 mm. The nomenclature used by the Swedish Environmental Protection Agency can be confusing at times, as it gives cartridges as calibre x case length. There are several cartridges with the same designation, which does not lead to clear classification.

Introduction To Norma-USA:

Norma Oryx:

Norma Kalahari: