Vern Humphrey
Member
The belted magnum was an early 20th century means of getting express rifle performance in a Mauser bolt action, it was not meant for double rifles. It was to give headspace control with the long tapered, shallow shouldered Cordite cartridges. When you see a double rifle made in a belted magnum calibre because of the decline of the superior rimmed cartridge, it will have the same trick extractors as for a rimless cartridge.
Your late Packard era advertisement and photo are interesting. By that time, a Packard was just a "badge engineered" Studebaker. The fins are right off the Hawk series of Studebakers.
Holland and Holland wanted a cartridge compatible with Mauser actions. But they also wanted a rimmed cartridge because they felt boring the chamber deeper was best in tropical conditions -- crud could be pushed forward as you chambered a round and wound up between the shoulder of the chamber and the shoulder of the cartridge. That required a rimmed case. But in Mauser magazines, rims can interlock, causing bad jams.
So Holland and Holland made the rim VERY thick -- too thick to allow one cartridge to get back far enough to interlock with the cartridge below it. Then to accommodate the Mauser claw extractor, they cut an extraction groove in the edge of the rim -- resulting in the belted appearance.