I had a Francotte 9.3x74r with a set of 20 bore shotgun barrels added by the previous owner. I found that the gun never handled well with the shotgun barrels. The pistol grip stock with grip cap and long tang, tang over the strap of the stock, slightly bolstered action, all caused to much weight at the rear.

Make certain if you do this, the gun is weighted properly for both applications. Perhaps 3" chambered 29" shotgun barrels with a solid smooth rib.