Just wondering if I have to do anything but collect money in order to sell an ar face 2 face.

Sorry all AR15 sales must go through me. You send me the gun & the other guy sends me cash.

Some buyers and sellers want to see some form of ID.  Some also want a bill of sale.

But when it comes down to it, it is as simple as you stated.

I sold my father-in-laws SKS for him and all I did was make a photo copy of my and the buyer's drivers licenses and then handwrote a "receipt" for it below our ID's, including the serial number and manufacturer and then we made a copy so we each had one and then both signed each one.

If you're selling I'd recommend getting the recipients name and at least city of residence. That rifle has YOUR name attached to it. If it later comes up used in a criminal offense, someone is gonna be knocking on YOUR door. It will be more believable if you can supply a name and address, than simply "I sold that gun back in September, '04".

If you're buying hand the guy the cash and get away quick. If it is later stolen, they'll be knocking on HIS door, and his response will be "I sold that gun back in September, '04". We'll probably find out about you from the theft report you filed, but what the hell.