Last night I watched a Nat Geo show called "Ghost Guns." Ghost guns are untraceable, unlicensed, illegal guns. Many of them are hand-made in the Philippines by artisans who create guns that are, for all intents and purposes, identical to manufactured weapons. The guns are even inscribed with fake numbers and manufacturer marks.
The guns are transported to the United States and purchased by criminals--gangsters, mostly, who use the weapons to rob drug dealers and to commit other crimes. As the weapon is used it leaves a trail of ballistic evidence. When it gets too "hot" the guns are often sold to criminals south of the border; Guatemala is a popular destination.
Fascinating stuff...and so many potential stories.