Sweden
In Sweden, it is possible to freely acquire air guns with a muzzle energy not exceeding 10 joules (7.4 ft·lbf). Air guns with muzzle energy over 10 J must be registered (gun license is needed).
Air guns are not allowed to be taken to public places without the consent of police.
Hunting with them is illegal without a hunting license.
Silencers are not allowed on airguns without a license.
Semi and fully automatic airguns are restricted to 3 joules (2.2 ft·lbf).
Read more about this topic: Air Gun Laws