Glenn is correct.

The last thing you want is have the gun classified AOW under the law. If it does not have a tax stamp currently, you can not get one. If it was originally so classified, it must have a tax stamp. It can only be transferred by a FFL III. While the collector book value may go up, the ability to sell it shrinks.

I went through this over a gun and finally decided the hassle just was not worth it.

Pete