A sabot is simply a sleeve that fits the bore of the rifle you shot(commonly used with ML or shotgun loads) to allow you to shot different diameter bullets. Ie: I shot a 45 cal bullet in my Muzzleloader(ML) with a 50 cal sabot due it being a 50 cal diameter bore. It takes up the gap(for lack of a better word) to allow the smaller diameter projectile(bullet) to be fired accurately and safely in the firearm of a larger bore.

Tell use what make and model as some guns can be adjusted with minimal effort, while other require a gunsmith. I am more than sure someone on here can help you out with a little more info.