I shoot Hornady .40 caliber 180 grain XTP and HAP bullets with .40/.45 MMP sabots in my .45 TC Hawken with 1:48 twist. They shoot quite well. The longer 200 grain SSTs and SW bullets do not shoot as well as the shorter 180 bullets.

Therefore, I would suggest that you try the shorter, lighter bullets, as opposed to the longer heavier ones, in view of the relatively slow barrel twist.