How can the FFL sell to non-residents? One of the things you must show is an ID. Typically a driver's license as that lists a residency. Even a military ID card will not suffice for the identification requirement since it doesn't show residency. See the link, go to page 179 and read about 4473's
http://www.atf.gov/pub/fire-explo_pub/2005/p53004/index.htm(D4) Who signs ATF Form 4473 for the seller?
ATF Form 4473 must be signed by the person who verified the identity of the buyer.
(D5) Is a Social Security card a proper means of identification for purchasing a firearm from an FFL?
No. A Social Security card, alien registration card, or military identification alone does not contain sufficient information to identify a firearms purchaser. However, a purchaser may be identified by any combination of government-issued documents which together establish all of the required information: Name, residence address, date of birth, and photograph of the holder.
The only way to transfer to a non-resident is to transfer to a licensee in the state where the buyer is a resident. In a city like Cincinnati, for example, a gun show might bring FFL's from Ohio, Kentucky and Indiana as well as potential customers. It is possible and legal for an Ohio resident to buy a gun from a Kentucky dealer by having the Kentucky FFL transfer the gun to an Ohio FFL to deliver to the Ohio resident. All the paperwork, bound-book entries, NICs checks, etc exactly the same as if the gun were purchased and shipped across country.
Given the scrutiny a bound book gets, who would be dumb enough to sell off the book and risk their livelihood and a free 10 year stay at Club Fed for a piddly few bucks?