Hiya,
Just a word to the wise about shipping older firearms through an FFL holder to a factory service center for repair.
First, some FFL dealers in less than friendly gun states will process your firearm through the NICS process before they return it to you upon it's return to them. If your firearm is pre-GCA'68 this will bring it into the registration DB. I had one dealer that said it was store policy to transfer the firearm to the bound book and then transfer it back on a 4473 and NICS check when it returned from the service center, needless to say, I haven't been back to them since. (Also, unless the law has changed since I had my FFL, repairs done "While you wait" do not require either a gunsmith service book nor a bound book entry as you are still there and haven't given it to the gunsmith. This will keep your pre-gca68 FA off the books)
Second, since all makers have lawyered up to the max, any trigger mods or other gunsmith work you have done to the action will, in most likelyhood be "repaired to factory specifications" in order to assure they cannot be found to be returning "out of specification" firearms. Case in point, I purchased an early TC Contender with a wonderful 2 lb trigger that TC used to have right out of the box, Since it was an un modified frame, none of my barrels would fit, I sent it back for the "Free modification", it came back with a fully lawyered up 6 Lb trigger that felt like I was dragging a steel trashcan down the driveway. Cost me a few hours of my time to stone it back to serviceable condition.
My 2 cents,
Tom