The only 257 WBY I ever worked with was a friends Ruger MKII rebarreled with a 26" Shilen and Brown Precision stock. It would push 90 grain X's at 3,780-ish (RL22) and group them under .5 for five shots. Wicked accurate rifle.
Though a "book load" I suspect it was pushing the envelope... however, I'm of the opinion that many guys attracted to rounds like the 257 Wby, 6-06 and all the Ai's are more prone to redlining than the average 308 shooter
“Perfection is Achieved Not When There Is Nothing More to Add, But When There Is Nothing Left to Take Away” Antoine de Saint-Exupery
