It is almost impossible to bring back firearms. My unit found a gold plated dragunov in an amnesty box. Our Bn Co and staff went through a bunch of hoops to bring it back as a piece of unit history but the customs guys confiscated it before we left.
The attitude toward war trophies has become more restrictive as we became more politically correct. Not to mention the importation restrictions have become better enforced. Basically we have mps acting as customs agents that basically search every vehicle and every bag as we leave country.