The text says Westley Richards made 5 different bullet designs for it.

as well:
"The cartridge itself had a long bottleneck to hold bullets firmly, a distinct taper to ensure ease of feeding, and – most notably – a rebated rim. It was the first major cartridge to use this design, in which the rim is smaller in diameter than the base of the cartridge. It was designed this way to fit the standard military Mauser 98 bolt face.

Military Mauser 98s were designed for fast loading using stripper clips that fit into a slot in the rear of the action and allowed five rounds to be “stripped” into the magazine with a sweep of the thumb. There was a thumb notch on the left side of the action wall to accommodate this. By making the .425 with a rebated rim that would fit into a stripper clip, Westley Richards was able to utilize the existing features of the cheap and readily available military Mauser action to create a magazine rifle for dangerous game that was faster to load than any other.