Straight rifling in shotgun barrels was a recurrent idea to improve shot patterns also. The theory behind this use: The straight rifling keeps the accelerating wad and shot charge from turning willy-nilly while going down the barrel and thus spreading the shot charge. The idea crops up about every 50 years or so. The earliest example I have seen was an 18th century single barrel gun converted to percussion. About 1870 Zimmer dismissed the idea as useless, obsolete bogus. Then there was an 1880s Austrian, Ferlach made 16 gauge with straight rifling in both barrels. Both guns were clearly shotguns, without rear sights. This Husquarna also seems to have the rear sight added as an afterthought. In the 1880s -90s Straight rifling was replaced by the more effective choke boring. But in the 1970s one American reinvented it. He used a cylinder bored, straight rifled barrel with an interchangeable choke screwed on and claimed much tighter patterns. IIRC I read about it in GD once.