I have made it from both 6mm Rem and 7/57 but generally just buy new 257 Roberts brass from one of the several sites that have had it available in the recent past. I don't know about today but have had no problem getting it as recently as 2 months ago.
edit: Cabelas has it in stock right now, 1Mar12.
Last edited by Notropis; 03/01/12.
