Talked with an ATF friend of mine who works in the regulation part of things, She said;
As per 27 CFR (Code of Fed. Regulations) sec 478.11, there are two areas to look at,
1) Definition of dealer which is;
Dealer. Any person engaged in the business of selling firearms at
wholesale or retail; any person engaged in the business of repairing
firearms or of making or fitting special barrels, stocks, or trigger
mechanisms to firearms; or any person who is a pawnbroker. The term
shall include any person who engages in such business or occupation on a
part-time basis.
2) Definition of Gunsmith is;
Gunsmith. 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 a term shall
not include a person who makes occasional repairs of firearms or who
occasionally fits special barrels, stocks, or trigger mechanisms to
firearms;
So there you have it.........kinda, sorta, roughly. If you're not in it for a livelyhood, regular biz, profit etc., one does not need to have a FFL.
So now you may ask, what constitutes the above? Answer???? There's no dollar figure or the like so that would be up for interpretation.
But they said, if you are investigated and they can show a substantial profit from gunsmithing, you'd better have a license.
Also you can keep a firearm overnight, without the owner being around as long as you didn't receive it thru the mail.