A bill of sale is useless for a used car as well... in Texas you need a form 130-U to transfer a car. They will not accept a BoS. For firearms which aren't registered or transferred or any such thing in Texas it's completely pointless and could potentially cause more issues than relieve.If you bought a used car from someone, you might as well expect they'd want a BoS. Why should a firearm purchase be any different?