Here in Sweden it's illegal to transport or store a weapon that's not temporarily rendered inoperable, ie firing pin removed etc and it has to be stored separately. The same goes for any ammunition.
It's not really a comparable situation to the US because of the 2nd amendment, but it cuts down accidental shootings to nearly nothing.
Also (with reservations that I necessarily don't remember correctly), to own a weapon you need to be a member in good standing for at least 6 months in a competitive shooting club OR you have passed a hunters exam which may allow you to get a license for hunting rifles.
On top of that, the police makes a background check to see if you have any past or current crimes on your record or any other type of history that may make you unfit to own a weapon (like mental illnesses, some types of physical illnesses or history of violence etc).
If you buy a weapon directly from another person you need apply for a license for that weapon with the sellers original license attached to the application. This is to stop legal weapons from being resold to an unknown third party. You are also legally bound to inform the police if your weapon has been lost and if it's judged you where careless in handling and storing it you may lose all your weapons (a license specifies exactly which weapons you own).
You also have to motivate WHY you want to own a specific weapon and how it's going to be used (in most cases this relates to people having different guns for different types of sporting events, but can also be applied to hunting weapons). This also means that weapons where the intended use falls outside competitive shooting or hunting will almost never be allowed to be sold.
Some of these rules applies to soft-air guns, paint-ball guns, bow & arrows and other missile weapons depending on the weapons projectile energy but generally speaking, if the weapons energy is below a certain threshold you don't need a license if you are 18 years of age or older.
