...law enforcement agencies nationwide embraced civilian versions of the military M4 selective-fire carbine as a long arm suitable for engaging heavily armed and armored felons beyond pistol range with greater precision and stopping power. This focus on deploying carbines only intensified after the 9/11 terror attacks, as agencies began preparing to deal with potential terrorist threats as well as criminal acts. SWAT and ERT teams first used these weapons, but they quickly spread to supervisors, and within a few years, officers and deputies. They are now euphemistically known as a “patrol rifles” and carried as a standard-issue long arm in patrol cars around the nation (even on some university campuses).
The widespread use of patrol rifles among law enforcement and the possibility of terrorism meant an increase in range time for many officers using their duty sidearms, and an almost entirely new law enforcement market for 9mm, 40 S&W, and 5.56 NATO/.223 Remington caliber carbines. When combined with China gobbling up core ammunition components such as brass, copper, and lead for their exploding industry, the shortage was simply explained by a massive increase in demand that has yet to let up.That's the largest 'black hole' for ammo. Second?
...demand only escalated as a result of the recession and the 2008 election. President Obama is no friend of the Second Amendment, which caused gun owners to stock up on firearms and ammunition in fear that the administration would push for a restoration of failed gun control laws that expired during the Bush administration. The economic instability of the recession and a resurgent acceptance of shooting sports also created many first-time gun buyers, many of whom developed into avid shooters who use significant amounts of ammunition.
A very interesting remark from a manufacturer:
Our information and research tells us that the increased demand is global, not just domestic, and the demand is still increasing further.