Wait! What? I need a license to carry ammo between states now? Since when?
...flight from Boston to Miami and on to Jamaica.
...several hundred bullet primers were discovered inside the bag after some ignited.
Loose primers it seems (which qualify as hazmat), not loaded ammunition, and was traveling internationally.
I would expect this wouldn't have happened with finished ammunition. Primers are typically packaged in cardboard and plastic containers that are easily crushed, after loading they are in the pocket of a metal casing and much more protected.