(21)
The term “engaged in the business” means—
(A) as applied to a manufacturer of firearms, a person who devotes time, attention, and labor to manufacturing firearms as a regular course of trade or business with the principal objective of livelihood and profit through the sale or distribution of the firearms manufactured;
(B) as applied to a manufacturer of ammunition, a person who devotes time, attention, and labor to manufacturing ammunition as a regular course of trade or business with the principal objective of livelihood and profit through the sale or distribution of the ammunition manufactured;
(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;