yea im thinking gas operated as well. the 357 has a good deal of pressure. im not sure if its more than a 7.62x25 or not.
i like the cut down 223 brass.
to form them when cut above the neck. Why not fire form them straight?? there are ways to fire form in dies also.
I think there are some cheap 357 or 9mm barrel blanks on numrich also there are some on green mountins site. ill look at my saved lins for others