John Boyd,
You say "certain" gun parts require a license. My question, if possible to answer here, is what about me, as a FFL holder, sending a couple of broken mainsprings to the maker in Italy, so they can replace them? I am doing this as asked for by the customer. My opinion is that if there is any possibility of my braking the law (and loosing my FFL), I sure as hell won't do that; let the owner take the risk. The are advantages in not having a license, under the radar, so to speak..
A custom gunmaker told me a few years ago it was very hard for him to get rifle barrels into Canada, due to US law, not Canadian as a result of 9/11
Anybody with info please chime in.