Without a legal requirement for you to report the sale or transfer of your firearm(s), a background check is nothing more than a snapshot. You can sell your gun the next day, or ten years from now, and the Feds know nothing of it.
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Universal background checks is code for all sales must be reported. All other transfers will be illegal.
Might be just a teensy bit unenforceable, unless a Stasi style network of informants is established, with a 1-800-DENOUNCE hotline.
Getting SWATd by one’s disgruntled liberal neighbor is already the nightmare scenario in some states.
Still, like dey say in da hood, “Snitches get stitches”.