Scorch is right.
Mrbatchelor - you don't need a FFL to work on your own stuff. Many do but that doesn't make Joe Hobby or Buffing Bob with his Dremel a gunsmith. Like Dfariswheel said, there is no standard or certificate for gunsmiths. The training or experience varies.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!