"Slug" barrels are offered in both fully rifled and smooth bore. As stated above a fully rifled barrel will produce poor patterns. Smooth bore barrels are offered in fixed choke and screw in chokes. The fixed choke barrels are usually cylinder bore or improved cylinder. Either would be fine with buckshot at close range. If your barrel has screw in chokes you can pattern it with the full, modified and improved cylinder choke tube to see which one patterns better. Obviously do not use a rifled choke tube with buckshot. MIKE.