18 USC 921
(11) The term “dealer” means
(A) any person engaged in the business of selling firearms at wholesale or retail,
(B) any person engaged in the business of repairing firearms or of making or fitting special barrels, stocks, or trigger mechanisms to firearms, or
(21) The term “engaged in the business” means—
(C) as applied to a dealer in firearms, as defined in section 921 (a)(11)(A), a person who devotes time, attention, and labor to dealing in firearms as a regular course of trade or business with the principal objective of livelihood and profit through the repetitive purchase and resale of firearms, but such term shall not include a person who makes occasional sales, exchanges, or purchases of firearms for the enhancement of a personal collection or for a hobby, or who sells all or part of his personal collection of firearms;
(D) as applied to a dealer in firearms, as defined in section 921 (a)(11)(B), a person who devotes time, attention, and labor to engaging in such activity as a regular course of trade or business with the principal objective of livelihood and profit, but such term shall not include a person who makes occasional repairs of firearms, or who occasionally fits special barrels, stocks, or trigger mechanisms to firearms;
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