For Sweden it's real easy, as long as it's not a functional firearm, or has ever been one (meaning deacts), then anything goes. If it has been a firearm or currently (as in live fire, lethal stuff) then you need a proper licence for that specific firearm secured through proper agencies (ie police) bore you are allowed to buy the item.
So replicas, air softs and air guns and such, with a total impart energy of less than 1 joule (the point where the projectile is capable of piercing the forehead bone) are a non-issue.