When you watch any war movie and realize you have in your collection more examples of the rifles used in production than you don't. And then you take this oppourtunity to make a check list of rifles you need to add to your collection.
When you've given up collecting Long Branch No4's based on year and are now on the hunt for every serial number prefix (0L###x, 1L###, 2L###x, 3L###x......)