I have owned and shot both, hunted with both, there is no difference to speak of...The 505 can be handloaded to more power than the Jefferys although in factory persuasion the 500 Jefferys was the hottest round. the Gibbs simply has more powder space any way you cut it.

On the contrary, the 505 Gibbs is as easy to make feed as the 500 Jefferys, maybe easier...Neither are a snap, thats for sure when working with a rebated case head, problems can exist, but that has nothing to do with the caliber, it does have everything to do with the gunsmith...

The 500 Jefferys can be built on a std. action, the 505 cannot..

I have never considered either of them a particularly well designed cartridge..