A gun registry does nothing for stolen weapons. Well I shouldn't say "nothing" it would probably victimize innocent owners of the guns used in crimes.
Here are some stats...
NCVS estimates there are 341,000 incidents of firearm theft from private citizens annually from 1987-92. That is not to be confused with weapons, each incident can include multiple firearms.
53% of the thefts of guns were handguns.
According to NCVS almost 43.6 million criminal victimizations occurred in 1993, including 4.4 million violent crimes of rape and sexual assault, robbery, and aggravated assault. Of the victims of these violent crimes, 1.3 million (29%) stated that they faced an offender with a firearm.
All stolen guns are available to criminals by definition. Recent studies of adult and juvenile offenders show that many have either stolen a firearm or kept, sold, or traded a stolen firearm.
The 1991 Survey of State Prison Inmates found that violent inmates who used a weapon were more likely to use a handgun than any other weapon; 24% of all violent inmates reported that they used a handgun. Of all inmates, 13% reported carrying a handgun when they committed the offense for which they were serving time.
According to the 1991 Survey of State Prison Inmates, among those inmates who possessed a handgun, 9% had acquired it through theft and 28% had acquired it through an illegal market such as a drug dealer or fence. Of all inmates, 10% had stolen at least one gun, and 11% had sold or traded stolen guns.
Studies of adult and juvenile offenders that the Virginia Department of Criminal Justice Services conducted in 1992 and 1993 found that 15% of the adult offenders and 19% of the juvenile offenders had stolen guns; 16% of the adults and 24% of the juveniles had kept a stolen gun; and 20% of the adults and 30% of the juveniles had sold or traded a stolen gun.
From a sample of juvenile inmates in four States, Sheley and Wright found that more than 50% had stolen a gun at least once in their lives and 24% had stolen their most recently obtained handgun. They concluded that theft and burglary were the original, not always the proximate, source of many guns acquired by the juveniles.
A study of adult and juvenile offenders by the Virginia Department of Criminal Justice Services found that juvenile offenders were more likely than adults to have carried a semiautomatic pistol at the crime scene (18% versus 7%).
They also were more likely to have carried a revolver (10% versus 7%). The same proportion of adults and juveniles (3%) carried a shotgun or rifle at the crime scene.
Over half of the guns that police agencies asked ATF to trace were pistols and another quarter were revolvers.
Trace requests represent an unknown portion of all the guns used in crimes. ATF is not able to trace guns manufactured before 1968, most surplus military weapons, imported guns without the importer's name, stolen guns, and guns missing a legible serial number.
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So when you factor in all of these stolen weapons, all of the guns that are untraceable for the reasons above (and I assume most criminals remove the serial number), the fact that juvenile offenders were more than twice as likely to have a semiautomatic weapon at a crime scene than a adult offender (hint: they didn't legally acquire it) and the expected low compliance resulting from an attempted national registry and you are left with butkus. A national gun registry turns into a giant witch hunt, and an expensive one at that while doing nothing to curb gun violence.