It is my understanding that the Mannlicher Schoenauer relies on the shoulder alone for headspacing.

When fireforming a raw 7X57, 8X57, or anything else with a shorter, narrower, shoulder the brass will likely be stretched, overworked, and weakened at or near the web.

The Shoulder of a 9.5X57 is rather slight to begin with. Fireforming a live round with a smaller, narrower shoulder could allow gases to ecape and /or blow back.

Drawing the brass out (expanding the neck), then sizing through proper FL dies would remedy either situation and the brass would be quite suitable. As indicated in previous posts, I have just purchased (and will use) a couple of boxes of very nice 9.5X57 loads from Reeds Ammunition Specialties that are made from new, straight walled, then properly sized 9.3X57 Norma brass. In the past I have formed and used brass made from .35 Whelen (through RCBS dies) that has performed flawlessly.

Reeds

I had previously purchased two boxes of 9.5X57 from another maker that were formed from 7X57 that apparently had not been necked up prior to sizing. The shoulders were 'stock' 7X57 dimensions, they went back.

I like my Mannlicher Schoenauer M1910. My preference is to not damage it.