If APDS and HE are designed to be fired from the same barrel, they don't need different twist rates. 

APDS and HE have been fired from common guns since the mid 1940's 

You might not get optimum of either with a particular twist rate, but you can certainly define a twist rate and design APDS and full bore projectiles to suit that.

Even if the finned penetrator is understabilised by spin alone ,it has fins for stabilization. 

Much longer projectile is obviously not stabilized by same twist rate as the shorter non ap projectile