OK so why then need a faster twist in the pistol. The lighter charge will not strip the patch but the rifling will still impart the 1:70 twist rate. Velocity will be less but the twist rate will still be 1:70 even after the ball leaves the muzzle.
And if stripping the patch is an issue with heavier charges (rifle charges) shouldn't patches fired from a rifle show signs of tearing/shredding from the rifling?
There may be another answer but I can't see it clearly. Does the slower velocity require a faster twist to stabilize the ball? If so, why?