They say that if only we'd give up our right to own firearms, we'd be almost completely free from gun related crimes. The murder rate would drop, and more importantly, mass shootings would become a thing of the past.

To some extent they are correct. If you live in a developed country with strict gun laws, you won't see very many crimes committed with guns. Although it's important to remember that in contrast, developing countries with strict gun laws usually see the opposite effect. Countries like Mexico, where buying a gun legally is difficult, often have an abundance of gun related crimes (as well as ordinary crimes).

But in theory it should work right? If you live in a stable, wealthy nation with a functional police force, gun control should be effective (though whether or not it would prevent violent crimes that aren't gun related, is debatable).