We have written a lot about both cartridges on various topics on the Forum in the last few months.
Currently there are two cartridges, the 500 Jeffery and the 12,7x70 Schüler, which cannot be used alternately in all weapons.
The cartridge 500 Jeffery is better suited to a Magnum action for many reasons. I don't know the experience of those who keep claiming that the cartridge 500 Jeffery is well suited for a standard Mauser 98 action.
The loads of both cartridges are not comparable because right from the start the cartridge 505 Gibbs was loaded with Cordite and the cartridge 500 Jeffery with platelet powder. This also partly explains the size of the cartridge 505 Gibbs.