Doing some searches on google suggest that a gun owner can sell his gun to anyone in his state as long as there is no probable cause not to. Receipts and background checks not required. Even if a gun is lost, there may be no legal requirement to report it. Getting the informatiom rom links in this thread among others
http://www.usacarry.com/forums/general-firearm-discussion/16370-privately-selling-handgun.html
Maybe this has been covered in this thread, but do most agree that gun laws may be a little lax when it comes to this? That if we don't want to restrict obtaining a weapon legally from shops, that we should do a better job tracking the guns that exist and their paper trail of where they end up? Even my car is required to be registered yearly, if I plan to not operate it or sell it the DMV needs to be notified, etc