This is a very thorough and informative article about what the UN is proposing to control arms worldwide and why it is futile.
Summary: Within a nation, severe gun controls, a firearms registry, and firearms transfer controls are items that have no effect on the guns owned, used, and rented by confrontational criminals (the violent criminals who choose to confront their victims). That is because they do not apply for a firearm licence, do not buy guns from legitimate sources, do not register their guns, and do not apply for a permit to carry an illegal handgun down to the bank to rob it. As a result, such a gun control system requires heavy expenditures (in tax dollars; no known gun control system succeeds in funding itself by any known fee system). The promised "reduction in violent crime levels" just does not happen.
The negative effects of a severe gun control system include:
1. The removal of firearms from the hands of victims, and the failure to remove any firearms from the hands of violent criminals.
2. The inability of the system to point to the name, address, or identification of the gun of the violent criminal because none of those are in the system.
3. The criminal perceives the system as offering him (the criminal) protection while he is committing any violent confrontational crime, because the system has either confiscated the firearm owned by the victim, persuaded the victim to stop owning a firearms, or forced the victim to lock up his firearm separately from the ammunition. All of those effects are highly desirable from the viewpoint of the criminal, because they make it safer for him to confront his victim.
4. Severe gun control laws are especially damaging to the interests of women. Women are the preferred targets of violent criminals, as the criminal believes that a woman is less likely to be able to protect human life from criminal violence during the inevitable period of time between the beginning of the crime and the arrival of the police (usually after the criminal has left the scene, because there was no way she could call the police any earlier).