When I bought a used 1911 a few months back, we drew up a bill of sale, very simple.
I, (seller) sell (firearm description) to (SomeKid) for $XXX.
We both signed it. Legal document? Hardly, but it isn't too bad. It works pretty good for a free state, as far as gifted guns go? Did not do anything at all. As NH noted, they are supposed to prove me guilty, which sadly they rarely do anymore. If the state chose to confiscate all my guns, the best way I could get back at them was file a theft report with the ATF, since some of my guns were bought under my C&R, and hope the ATF nailed them.