i use a personal firearm record it has make caliber gage model serial barrel lengh finish action condition and it has spots for acquisition and disposition. which tells where when and how much you bought it for and tells who bought it from you how much when and has a place for both of you to sign
The key word there is required, the state does not require any documentation on sales by private citizens. I highly suggest getting a copy of thier drivers license and write up a bill of sale listing the guns make, model, and serial number. Last sale I did, I also wrote a statement on a paper that said the buyer agreed to not being a Felon or a person not legally allowed to own a firearm. Make two copies of everything and have it signed by the buyer/seller. Granted, this may not be enough in todays world of modern lawyers, but it might help. I keep copies of all sales locked up for future reference just incase.
This all pertains to in state sales only, I do not perform sales across state lines because unless I am wrong there are some federal laws forbidding it without proper checks and balances.