Many people shoot a .44 caliber bullet out of a plastic sabot in their .50 caliber muzzleloaders. A common .430 diameter bullet of .44 caliber is often used. Just be sure to get the right sabot for the bullet. If the .44 caliber is .420-.430 diameter then use that sabot VS the .451-.452 which are commonly used in the .45 caliber. Also the bullets your friend makes, try and have them made out of pure lead, although I shoot pistol bullets out of mine all the time. Just check your bore for copper and lead fowling from time to time. A good solvent and a bore brush will remove that.