In contrast , the United States ' constitution prohibits laws which disallow firearm ownership outright and owns about half of the world 's guns .
Countries such as the United Kingdom and Australia have changed their gun laws in the wake of mass shootings .
The United States ' constitution prohibits laws which disallow firearm ownership outright and owns about half of the world 's guns .
Countries such as the United Kingdom and Australia have changed their gun laws in the wake of mass shootings .