Before exporting firearms (0A501.a or .b, 0A506, 0A507, short-barrel shotguns) or ammunition (0A505 except .c) under License Exception BAG, regardless of value or destination, the traveller must submit CBP Form 4457 (Certificate of Registration for Personal Effects Taken Abroad) listing each firearm's serial number, make, model and calibre, and present a copy on return.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.