I agree with the guys above.
The 505 is likely too long for the std. large ring action. It is a length issue not a strength issue.
All original 505's were on the mag. action, in fact, IIRC, most of the modern magnum actions such as the Johansen are even a little bigger than the original Mausers.
If you cannot come up with a magnum Mauser action, you could always use a Ruger mag. action or a CZ mag action or simply buy a Ruger to rebarrel or try the CZ.
Better yet, build a 500Jeff and the Mag action becomes a moot point.