What did your friend's post office do about verifying that the packages contained rifles, and that they weren't loaded? Did they accept his written certification?
What would he have done if they had insisted on physically inspecting each firearm (which they have every right to do under the law)?
I mailed them, there was never any issues. They asked what it was (bought insurance), told them - all they did was ask if the gun was secured inside the box - was no big deal. They saw me several times over the course of a few weeks - as did the Fedex guys for others - neither had any qualms