"Firearms are designed to deliver ammunition. Without ammunition, firearms are no more dangerous than any blunt object, causing some scholars to refer to ammunition as the 'actual agent of harm.' While firearms are subject to various regulations (including licensing of dealers and background checks on prospective purchasers), ammunition is largely unregulated.
Laws regulating the purchase and possession of ammunition can help limit access by children, convicted felons and other prohibited persons, and can reduce the threat of firearms in the hands of these and other dangerous individuals."
Source: http://smartgunlaws.org/ammunition-regulation-policy-summary/