I guess your response confused me. As the bullet leaves the barrel its rate of spin is determined by the twist rate and the velocity. This rate of spin doesn't decay much as the bullets velocity is shed. But how can you say that a higher velocity wouldn't make the bullet spin faster? I don't recall the twist rate of a .30-40 barrel, but I'm sure you could get by with less in a .300 ultra mag. I don't shoot one of those, so I don't know what rate they come with.