257wby mag

Yes, you can form .257 Wby cases from 7mm Rem Mag cases, but the neck of the resulting case will be short.  The SAAMI OAL of the Wby case is 2.549" vs. 2.500' for the 7 Rem case.  The brass may stretch some in the fireforming process, though, but your neck will still be somewhat short.  Dimensionally, the two cases are the same from the rim to the start of the Wby shoulder radius and the length from rim to shoulder/neck transition, but the neck itself is shorter on the Rem case.  Pyro is correct that the .264 Win Mag would be a better case to use, since it is identical to the 7 RM case except for neck dia and shoulder to neck transition height and would require less neck sizing.  But, the .264 brass is harder to find.  You can probably just run either case in a .257 Wby mag FL sizing die with not too much effort, then fireform.  The Wby double radius shoulder will form when you fireform the case. 

 

Roy

Model 700™ LSS

For wilderness or high-country pack-in hunts that involve rigorous hiking, we make the handsome, element-defying Model 700 LSS. Extremely lightweight, they feature a black laminate gloss stock, 26" clean stainless barrel, the new X-Mark Pro trigger and available in 257 Weatherby Mag.   Model 700™ LSS Features All the great features of our time-tested Model 700 26" clean stainless barrel Black laminate gloss stock X-Mark Pro™ Trigger Caliber Mag. Cap. Barrel Length Rate of Twist OA Length Avg. Wt. (lbs.) Order No. MSRP* Model 700™ LSS Specifications .257 Weatherby Mag 5 26" 10' 461/2" 7 5/8 84099 $972

i know i really want order one, but in lieu of the surgeries my daughter has in store for her in the next year or so, its going to have to wait they look sharp in the lss and the cdl both