Fellow Beretta enthusiasts:
That idea has crossed my mind and maybe the question can be posed on the BerettaForum.com [url]http://www.beretta-forum.com/[/url].
Meanwhile, my latest Jerry's Sport Center, Inc. flyer lists a "new" Beretta Cougar 835 in .357 SIG.
I don't know any more about it, other than there is a Beretta in that caliber being made available.
I'd prefer the 96 platform, though. The interchangeable barrels would be a blast, especially a longer/ported one in the .357 SIG.
As for the magazines, theoretically they should be useable in both calibers.
I will state that I would prefer a hot .40 or even a 10mm in the 96 or Cougar platform, respectively. But, the .357 SIG is a good cartridge in its own right.
Check out the Beretta Forum and see what they can offer in the way of information.
(I went there and posed the question already under the Topic title---"Berettas in .357 SIG"---I am [b]CENTURION[/b] on that Forum.)