Frank,

There are two possible reasons to have straight rifling. The first is to allow the use of a lead slug. The second is to stop any possible spin of the shot column. A straight rifled barrel will act as a spreader. In some tests at short range, it will provide a more even pattern than cylinder choke.

Here is an article about it by Bill Hanus:
http://www.gundogsonline.com/Article/pictures-are-worth-a-thousand-words-Page1.htm

Husqvarna shotguns had an option of a second set of barrels with cylinder choke and straight rifling. They would fire tight fitting lead slugs. It has to do with Swedish game laws regarding Moose hunting. Thus allowing a hunter to only have 1 gun and take a wide range of birds and game. Same concept as the drilling, yes? Except the drilling was even more of an adaptation to the game laws and hunting style. From my understanding, a hunter could be invited not to come back if they did not kill a fox they saw while hunting.



Pete