I'd like to respectfully offer clarifications to statements made by several earlier participants in this thread. I am not a lawyer and nothing here should be construed as legal advice. But, I believe that I can document everything that I say below.

There are two ways that a firearm can become, by federal legal definition, a "curio or relic" (or "C&R eligible"): (1) Once 50 years have passed since a particular gun was manufactured, that gun automatically becomes C&R eligible, as long as it is in its "original configuration." (Note: Major changes, such as "sporterizing" a military rifle, resets the 50-year clock.) (2) Specific models or specific individual firearms can be designated by ATF as C&R, even if they are not 50 years old; those so designated are placed on the published list, which is periodically updated. There is a process for petitioning ATF to place a particular model or a specific firearm on the list. (By the way, while there are many engraved commemorative guns on the list, a gun is not C&R eligible merely because it is engraved!) The firearms that are commonplace but more than 50 years old are just as much "curios or relics" as those that appear on the special ATF list.

When you are first issued a C&R license, it is not required that you enter all your previously owned C&R-eligible firearms into the required "Acquisition and Disposition record," usually called the "bound book" (although it can be a loose-leaf book.) What is required is that "each receipt and disposition of firearms curios or relics" be recorded in the book. [27 CFR 478.125(f), italics added for emphasis] Thus, you must record each C&R firearm that you acquire during the time that you hold the license -- even if you didn't refer to or "use" the license when you purchased that particular firearm. And -- here is where some collectors get confused -- you must record the disposition of any C&R firearm in the book, during the period that you hold the license -- whether or not the acquisition was logged. For example, if one of the firearms that you owned before you were issued the C&R license "turns 50" after you get the license, and then you sell it, you should record that disposition in the bound book, because you are disposing of what has become a C&R-eligible firearm. But if you don't sell it, it need not be logged in the book, because no acquisition or disposition has occurred.

It is not accurate to say that "ATF can drop by and legally inspect the book anytime." The law authorizes ATF to inspect the inventory and records of a C&R license holder only once during any 12-month period (and the inspections may be far less frequent than that, depending on local ATF priorities). The collector is contacted in advance to schedule the "audit," and the law specifically gives the collector the right to have the inspection conducted at the nearest ATF office if he prefers. Most collectors find inspection in the home to be more convenient, however.

Aside from the audits, a collector might be contacted during an active criminal investigation -- for example, if agents are tracing a gun used in a crime -- but they cannot enter your premises without an invitation. If the ATF believes that a collector is himself is engaged in criminal activity, they may enter the premises without an invitation only if they first procure a search warrant, based on probable cause, from a federal magistrate.