Whenever I compare so-called “assault weapons” with hunting guns, someone points out that assault weapons are designed for military use. How could it be that they’re often less dangerous than deer rifles?
The answer lies in the difference between military guns and their civilian counterparts. Take the AR-15, which served as the inspiration for the Bushmaster .223. The versions of this gun that the military actually uses, the M16 and its variants, are able to fire fully automatically — meaning that when the shooter holds down the trigger, the gun sprays a continuous stream of bullets — or in three-round bursts. This high fire rate makes the gun hard to control, and using smaller bullets reduces recoil.
But the AR-15s that are widely available for civilian use are not fully automatic or burst weapons — these features have been removed, and with them a major reason the military would want to use such a small caliber. What you are left with is a gun that was designed as a machine gun, and still looks like a machine gun, but functions like an ordinary rifle.
UPDATE: Thanks to commenter doobie1961 for noting that the military uses several variants of the M16, not all of which have a full-auto mode.