Years ago I spoke with a gunsmith about bringing in my .22 long-rifle to him for repair.
He said, “If you got the gun from your Grandfather when he died, you had better try to repair it yourself. Each month the ATF picks up a log book from me to take to their office and register serial numbers that are to be logged into the book any time a gunsmith works on a gun. That means rifles as well as hand guns. If your Grandfather never registered the gun, then keep it hidden as a family heirloom. It is against the law for a gunsmith to work on a gun of any type and not write down its serial number for the ATF to collect at the end of each month. In effect, it is a backdoor gun registration idea.”
In order to backup what he told me I did some research at the ATF website http://www.ATF.Gov and verified what he told me as correct.
According to their own publication, The Federal Firearms Reference Guide from 2005, on page 185 states the following:
Does a gunsmith need to enter in a permanent “bound-book” record every firearm received for adjustment or repair? If a firearm is brought in for repairs and the owner waits while it is being repaired or if the gunsmith is able to return the firearm to the owner during the same business day, it is not necessary to list the firearm in the “bound-book” as an “acquisition.” If the gunsmith has possession of the firearm from one business day to another or longer, the firearm must be recorded as an “acquisition” and a “disposition” in the permanent “bound-book” record.