So the Department of Homeland Security has a contract out for 24 million rounds of .357 Sig ammunition, apparently they did not want to use the term "Hollowpoint" so they called it "Duty" ammunition instead. But obviously they did not specify "Training" ammunition, which normally is cheaper.
Outside of certain governmental organizations like the Federal Air Marshalls, and the Secret Service, .357 Sig ammo is not a vastly popular round. It is basically a .40 caliber case necked down to accept a 9mm bullet.
Who knows what it means, other than that a relatively small number of federal agents are expecting to do a whole hell of a lot of shooting, or they are expecting the ammo market to dry up for an extend period time; sorta like what happened during World War 2.