Cerrosafe or Cerrobend are what you use for chamber casting.
This model was retailed in .308W and the rifle is marked .308W.
Why even bother?
This is no longer a Swiss Military Rifle.
It is now a Golden State Arms/Santa Fe rifle, sold here either by International or Globe.
If you want to spend money on the critter, find it a Magazine and contact friend diopter on this forum, who has Scope Mounts for these!
These are somewhat clunky looking, but they are real precision.
They are also reliable, lightning-fast and accurate.
What more can a guy ask?
BTW, the "Rubin" of the rifle's name developed the ammunition.
He was ALSO the direct father of the .303, so he definitely knew what he was doing!