Very few guns are smuggled into the US. So other than legal gun purchases being used to funnel into criminal hands, the only possible source of crime guns is theft from dealers and theft from those who legally bought the guns from a retailer. Those thefts would always be reported prior to gun winding up at a crime scene (guns that are only claimed "stolen" after they turn up at crime scenes are those resold by legal owners trying to cover their ass). The number of guns legit reported stolen prior to use in a crime are a fraction of the number of guns entering the black market each year, so the only logical possibility is that most of them are the result of legal dealers and buyers selling them to criminals, which they can legally do since there is no way to prove they knew the person was a criminal.
And what's the source for the number of guns reported stolen? Who is even keeping track?
The ATF investigates the source of guns being trafficked in the black market.
"they[Federal Firearms Liscensed dealer] were associated with nearly half of the total number of trafficked firearms documented during the two year period"
"Straw purchasing was the most common channel in trafficking investigations. Almost half of all the trafficking investigations involved straw purchasers." "Straw purchasers buy guns for other unlicensed sellers, criminals, and juveniles."
"Unlicensed sellers were a focus of about a fifth of the trafficking investigations." "Unlicensed sellers buy guns with the purpose of reselling them."
"Firearms stolen from FFLs, residences, and common carriers were involved in over a quarter of the trafficking investigations."
And note that "stolen" from residences includes guns stolen from fellow criminals who often bought their gun via corrupt dealers, straw purchases from legal gun owners, and unlicensed sellers who also sell legally under current law.
In sum, less than 25% of guns trafficked in the black market got there by being stolen from someone who possessed the gun legally. Most of the rest get are funneled via retail sales from legal dealers to gun owners who are buy them directly for particular third party criminals or buy them in order to resell them to traffickers, all of which is legal under current law unless it can be proven that the reseller knew they would selling to a criminal (which cannot be proven unless it's a sting operation).
And there's no requirement to report a theft, if you're not going to file an insurance claim there's little reason to report it.
Someone steals a $300-$1000 piece of property from you, most likely by breaking into your property while stealing other things and you have no reason to report it? A deadly weapon that was stolen from you by a criminal (by definition) and thus may wind up used to murder someone, and you have no reason to report it? That's some stunningly disingenuous nonsense even by your standards. The only reason people wouldn't report a stolen gun was b/c they themselves are a criminal and don't want to draw attention of the police.
Also, 11 states make it a crime not to report a stolen gun, but yeah that is yet another Federal law that that is needed: Jail time for not reporting a gun that has been missing for 60 days, and automatic liability for any crime your gun is used in if you fail to report it stolen.
Combined with registration of every gun, annual proof of possession, and a total ban on all gun exchanges outside of licensed channels with full background checks, reporting requirements for theft will make the current widespread practice of trafficking by thousands of "law abiding gun buyers" an high risk proposition with likely jail time. Yet it would have no major impact on an actual law abiding gun owners who are not engaged in trafficking to criminals, beyond the same impact of car registration.