The grooves on the " rifled" slug act like a fan in the wind and get the lead spinning. A sabot, on the other hand, uses the rifling of the barrel to get the plastic spinning which, in turn, gets the sabot spinning. The plastic falls away eventually and you have about a .50 caliber regular bullet heading toward the deer.

I agree with everybody else -- experiment with various brands. Mine, unfortunately, likes the really expensive Winchester Supreme Gold Partition (Mossberg 695 Slug Gun).