The way to check without spending a lot o money is as follows:

Make a threaded shank out of mild steel with the correct threads and fit it for the extractor. It needs be only about 3" long. This will be your false chamber. Drill a hole clear through it about .003" over the size of the cartridge head and chamfer it.

Now load your mag with the 9.3X57 and see if it feeds. You may find you need to load the ammo and seat the bullets a bit deeper then factory specs, but many times it's possible with no ill effects. If it works with the false chamber it will work with a real barrel.

Because the shoulder of the 9.3 is smaller in diameter then that of the 9.5 I'd expect the nose of the bullet to come in lower on the chamber (remember to chamfer it) If it's way too low you may find it's harder to make modifications then it's worth. But this false chamber is something that can be made in an hour or less, so it's worth the time to try it.

If it will not feed the 9.3X57 it may be lower cost to you overall to simply have a new barrel made in the original 9.5X57 chambering. A standard .375 bore barrel as you'd use for a 375H&H works fine. Not as easy as a Mauser to rebarrel, but not overly difficult either.