A 10-twist in 257 Weatherby will stabilize all available “factory” bullets of 100-120 grains. Bullet makers essentially make short stubby bullets in 25 cal to work with the 10-twist limitation. There are some good bullets in 25 cal but none with great BC.
The 131 Blackjack is another matter. Not commercially available in ammunition and you have to have a special twist barrel. It looks like they recommend a 7.25-twist for the Blackjacks. And I don’t know if it’s a good hunting bullet or no.
