Twist rate will have more to do with it then anything if your using a 5-6 groove barrel.
A 1-10 is as fast as I would recommend with that bullet. The 257 STWs I have built will on average get you around 3550 to 3575 fps with decent case life. Those numbers are out of Lilja barrels with the 115 gr Ballistic Tip so you may get slightly different numbers but similiar.
If your breaking 3500 fps you should start paying attention to pressure signs closely working up from there. Every 257 STW I have built and tested would loosen primer pockets quickly at any velocity much over 3600 fps with this weight bullet and this barrel length.
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