The U.S. Army has seen its small arms ammunition (5.56mm-12.7mm) expenditures grow from 600 million rounds a year in 1999, to 1.5 billion rounds today. Usage is expected to grow 1.7 billion rounds a year over the next five years. The army has one very large ammo factory at the Alliant Lake City plant in Independence, Missouri. But this plant can only produce 1.2 billion rounds a year, and expanding that production capacity to 1.5 billion rounds will take 12-18 months. Meanwhile, the additional ammo is being bought from civilian manufacturers. 

Why does the army need nearly a billion additional bullets a year? Well, since September 11, 2001, live fire training has increased considerably. Thats where most of it is going. Not only are the half million active duty troops getting more training with live ammo, but the 600,000 National Guard and Reserve troops are also firing more real bullets. Although the army has introduced a lot of electronic rifle ranges, these are seen as less useful than live fire exercises. The army also noted an increase in confidence, morale, and combat effectiveness, among non-combat troops that had been given a lot of time at the rifle range, and lots of ammo to fire off there. Previously, these troops would fire their weapons only once a year. Since these troops are not expected to be as good a single shot marksmanship, they are practicing a lot more with automatic weapons (5.56mm, 7.62mm and 12.7mm machine-guns). That uses up a lot of ammunition, but the non-combat troops become at lot more accurate, and deadly, quickly.