DHS bought less ammo last year than it did last year, and a LOT less ammo than it did two years ago.
They only bought a bit over 100 million rounds last year, and since they plan to spend about the same amount of money this year, it's going to be about 100 million rounds this year.
Any ammo shortages have NOTHING to do with DHS; they're caused by panic buying in fear of gun control after Newtown, and panic buying caused by stupid articles inducing fear of a non-existent DHS-induced ammo shortage.