I think you will find that a good sabot gun will often shoot a wide range and varity of bullets if you have sabots that fit the barrel well. I usually use the Greenhill formula to determine a little bit about which bullet will work good and what percentage of the bullet weight I should use to pick a starting point for the powder load.
I will go in both directions from that point in 10 grain increments. Once I find the 10 grain load which shoots best I try 5 gr each way to see if there is a better load. I often find that a bullet will have two loads one light and one heavy that will shoot good. Lee