257 Roberts max charges are pretty tame in the overall scheme of things. This is similar to the 250 Savage.
I recently formed some 22-250 brass for my 250 Savage, regular, not AI. I seated some 90 grain Sierras so they'd be firm into the lands, and loaded them with a full load. The cases fireformed quite nicely. Bolt lift and extraction were smooth and easy, and primer signs indicated a load that was still quite mild.
You're blowing out the brass to a larger chamber, which would lower pressures even more.
If you want to be prudent, you could make up a series of one each at increasing charges to get a feel for it.
