Why don't explosive detecting dogs smell owners gunpowder?

From:  "Hernandez, Shanira E. PVT 159th Med Co (AA)"

Why don't explosives detecting dogs alert on the gunpowder in their handlers side arms? In other words...Explosive detection dogs have handlers, almost all handlers carry a weapon, and all bullets in those weapons contain gunpowder. Why don't the dogs sniff it?

C.H.U.D. sent us yet another answer to clear up a question:

 Bomb-sniffing dogs (as well as drug-sniffing dogs, no not Gary Busey) are directed where to sniff by their handlers. They only put their noses where they're told. The handlers simply don't direct the dogs to sniff their guns.
 

Meg White confirmed C.H.U.D.'s answer with her thoughts:

because they are trained to only smell certain things and gunpowder isn't one of them