The straight rifling was an economical way to circumvent the Swedish game laws that put a ban on hunting moose with smoothbores; you had a "rifled" bore for the moose hunt, but you could still load the gun with shot and go birdhunting without destroying the shotpattern, as a true(spiral)rifled bore would have done...
Straight rifled guns were made from both percussion muzzleloaders and breechloaders, although I cannot state exactly when these game laws came into effect....
I personally own a Husqvarna M1860 (popularly named "Wrede's rifle", after the inventor) that was originally approx. .47 cal., then sporterized and reamed out to smoothbore; it is now approx. .52 cal. straight rifled.