Is your barrel threaded for choke tubes?
If it is, try buying a rifled choke tube for it. Then pattern it and compare the pattern to the pattern of an open cylinder tube, and also the pattern of an Improved Cylinder tube.
Repeat this procedure with both Foster slugs and sabot slugs. A total of six patterns.
If it is not threaded for choke tubes, it should be either an Open Cylinder or Improved Cylinder barrel. Pattern whatever fixed choke you have with both Foster and sabot slugs.