Foot note and you likely are already aware, but back in the day a lot of the 257 Robert’s ammo got converted to fit the WW2 imported Japanese Arisaka (sp?) rifles. Guys would just expand the neck a bit for the larger Japanese caliber. The size escapes me now but I remember it caused all kind of issues since the head stamp remained Robert’s. Be careful with old ammo you might find for it. It is still loaded commercially and that might be a safer source for brass vs picking up the infamous zip lock at the gun show with the sharpie caliber wrote on the side!