That quote isn't correct. You could buy a dozen shotguns, a pistol, six bolt action rifles, an AR15 and a hundred AR lowers..........and no multiple sale form is submitted.
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Report of Multiple Sale or Other Disposition of Pistols and Revolvers is submitted when a buyer acquires two or more handguns from the same dealer in a five business day period.
This applies to every licensed dealer.
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Report of Multiple Sale or Other Disposition of Certain Rifles "Certain rifles" are semi-automatic rifles larger than .22 caliber (including .223/5.56 caliber) with the ability to accept a detachable magazine.
This only applies to FFL's licensed as 01Dealer or 02Pawnbroker in CA, AZ, NM and TX......no where else.
The time period is the dealers actual business days, not just Monday-Friday. If the dealer is open only weekends, then Saturday/Sunday, followed by the next Saturday/Sunday would be four business days. Buy a gun that third Saturday and he files a Multiple Sale report.
If I sold you a handgun today (Tuesday) and you next bought a gun Friday....only four days has elapsed. I submit a form to ATF. If you had waited until Sunday, no form.
When such transactions occur, the dealer faxes or emails that report to ATF at the end of that business day, followed by mailing a hard copy to the local LE agency, as well as stapling a copy to your Form 4473.
I email in about four of those forms a week. The only times I'm aware that a customer was contacted by ATF was on the purchase and transfer of ten Beretta pistols and four AK rifles.
The Berettas were bough by a collector while he was out of the country for several months. ATF paid him an in person visit asking if he was reselling the guns. He was a collector, and they left. Subsequently he's received numerous multiple sales and ATF hasn't bugged him.
The other was a customer who bought four Hungarian AMD65 AK's for "bug out bags". ATF again wanted to know if he was reselling. He wasn't, but got very upset and made some stupid comments and left messages on the ATF agents voicemail that could be perceived as threats. Later he received a cease and desist letter as a result of his "flipping" guns hobby. That letter told him all his transfers must be through an FFL.
A few years later he was caught stealing a gun at a gun show, had to sell off all his collection for legal bills and eventually committed suicide. Never went to trial.
While "structuring" of financial transactions to avoid bank reporting requirements is a crime, that doesn't apply to firearm transactions. But IOI's ain't stupid and easily see the same name on those 4473's. They'll ask why three guns arrived the same day, but the buyer picked them up one at a time over three weeks to avoid that report. Yeah, they'll make notes on him.