Twist is 8 1/2. Already fire formed .243 cases and tested some Hdy 75 gr BTHP with very good results using H414.

What data I have found is for lighter bullets. Any experience out there using the heavier bullets? sundog

Sundog, I have a Mark II but heaviest I've shot is 50 gr. I make my cases from Rem 308 competition cases with the small rifle primer pocket.