i shoot a 505 Gibbs and absolutely love the cartridge! i have developed a number of loads ranging from a 600gr cast gas checked bullet at 1850fps to a 600gr Peregrine solid at 2250fps. load development is tricky with the Gibbs because of its case size but ive found heavy monometal bullets to perform the best since they take up much of the case. the 500 Jeffery would probably be easier to develop loads for due to the smaller case. however the 500 Jeffery presents its own list of issues ranging from feed issues caused by a rebated rim to neck tension issues cause by its very short neck.

however a word of caution, both the 500 Jeffery and the 505 Gibbs can pose serious magazine issues. its no small task trying to get them to properly stay in the magazine due to their massive dimensions.

-matt