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Due to Barrel tolorances and harmonics that is a very diffacult question to answer.
I would suggest you find some shooters of muzzle loaders in your area if you can and get some of the different sabots available in particular MPP12-MPP-HPH24 AND the Harvester Crush Rib pick up some of the standard bullets that shoot good in a wide range of guns, as an example ,the Shock Waves and the 250 and 300 gr XTP and Gold Dot. Then go home and pull your breach plug and try the different thicknesses of sabot with some of the bullets find a sabot that is snug enough that you really have to push to get down but is not so tight that you have to pound on it or that wont load smooth. I use either a T handle or a wood ball with a ramrod size hole drilled half way through. I will stress the importance of being able to load smooth so you get the same pressure on the load each time, a lot of people that are not reloaders do not understand the importance of wad pressure or thewhat amounts to the same thing; if you wantit to shoot good groups this is a must.
That said, to loose will not shoot good and if the bullet or sabot and bullet do not stay put they will act as a barrel obstruction which is dangerous.
There are some other sabots available if none of the ones I mentioned give you the right fit.
If you are looking for fine accuracy you will have to run the powder ladder and try a number of bullets, if you are looking for hunting accuracy for 100yds or less then you might try the pellets in 100gr[ two 50gr pellets] with the 250gr XTP Shock Wave and Gold Dot, if they wont shoot in you gun try the 300grs if they wont then start lookin for whats wrong like a loose mounting bolt or scope or scope mounts. It is good to wipe between each shot with a damp patch [cleaning fluid like windex with viniger or alk & winshield warsher fluid 50/50].
Always be sure that your bullet &sabot is tight on the powder it is not safe to shoot other wise.
If you have any questions there are a number of people here with many years ofdifferent kinds of muzzle loader shooting that will try to give you an answer, you will soon be able to tell who they are. Lee