7.75 works fine in a 257 Wby.I believe you don’t need a 7 twist in the Weatherby. On blackjacks site I think they list recommended twist rates. 7 twist falls in on 25-06 and 25-284. In my 25-284 I went 1-7.25”. Only concern would be over rpm at the Weatherby velocity and the bullet coming apart. Now with a 128 hammer it would be awesome.