I can make them in whatever diameter and weight you want. Diameter needs to be determined by the available shot cups, or sabots if you can get them. Also, the barrel must be rifled to make solid bullets stabilize. For smoothbore, slugs need to be well designed hollow base to get the shuttle cock effect which makes them fly true. Best way to produce them is to cast the blanks then swage the slugs, which takes speical swage dies, which are expensive.
