In my experience, if the shipper checks the box that says "Adult Signature Required", FedEx will not even SPIT on your doorstep if you're not home, no matter if you have all manner of waivers, forms, and signatures on file or not.
[Edited to say - it doesn't matter what it is, and some shippers have the habit of checking that stupid box whenever you order a $30 video card - which makes life miserable for me, since I live alone, 40 minutes from nearest FedEx location.]
UPS on the other hand, has left ammo every single time I've had it delivered.
An NFA dealer buddy once told me that "Brown" once left a 1928 Thompson on his doorstep. He took the package in, unopened, asked to speak to a supervisor, and demanded to know why the package was left. Brownshirt is thinking, "what's the big deal, yada yada yada, we got boxes to deliver, going back makes more work." So he opens the box with her watching.
Wish I coulda seen them eyeballs. I sure hope he picked them up off the floor for her.