Unfortunately since there is no standard to barrel bore diameter in muzzleloaders... they use the "as long as its close to" measurements... there is the need for different thickness of sabots. They vary by manufacturer, their ability to handle magnum charges VS regular charges, and their thickness of course. Be very sure of the diameter of your bore. Slug the barrel if you have to. Then pick a sabot to match the kind of projectile you want to shoot that will give you a firm tight, pressure sealing fit. I am not saying you have to drive the thing down the bore with a hammer mind you, but in a sabots case, too loose can often mean poor accuracy.

Sabotloader is a good source of information on sabots. I go to him when there is a rifle, sabot/bullet combination that just does not seem to work. He normally has good advise, and seems always willing to help. No matter how many times I have asked.