Re: 257 stw 100 gr barnes X
First, they are different bullets an require different seating depths. Your 115's probably shoot best .010 to .020 off touching the lands. The Barnes need to be at least .050 from the lands. I don't know what freebore length your chamber has, but if it requires the Barnes to be1 or two grooves out of the case(highly unlikely) it shouldn't matter Just make sure you give the Barnes that .050 start and you will like how they shoot. They will do 3660 out of my 257 Wby while shooting into less than .350.