I'm looking at a Sodia cape gun (SXS 6.5X58RX16 ga.) that needs a LOT of work. Before I get too involved, I'm trying to find out if the rifle caliber can be rechambered to something more readily available and effective.

I can't think of a modern or readily available european calibre that you can rechamber to. The barrel diameter is smaller than the usual 6,5 mm's like the 6,5x55. A german reloading manual recommends the use of a .257 bullet as the original bullets are no longer manufactured.
The non-metric calibre that comes closest is the 25-35Win, but it's some .15 inch shorter than yours.
The german company Kettner still sells ammo manufactured by W. Romey but you will have to pay some USD 9,- per piece!!

Dutchgus

Thank you! Your information about the .257 bore and the $9 US per piece for ammo put me over the limit on this project. I guess a hammer Sodia cape gun for $800 is too good to be true.

Best regards,

JPS