also, no records at all were kept before 1968.
That same 1968 Gun Control Act also prohibited interstate sales of guns via mail order except for holders of Federal Firearms Licenses. You can get one, but a friend who has one says it doesn't pay, except if you trade a lot of firearms each year.
You can buy a firearm online, but you have to pick it up from a licensed gun dealer in your state, and pay that dealer a fee.
