The AR-15 was designed by Eugene Stoner while working for the Fairchild ArmaLite Corporation in 1957. It was originally chambered in 7.62mm but was latter chambered in 5.56mm. Though today you will find them available in just about any caliber imaginable.
Due to financial problems, the AR-15 design was sold to Colt. Since 1958, Colt continues to produce the AR-15 later named the M-16 when adopted by the US Government. However there are many variations and manufacturers of this rifle available today.
While the AR-15 and M-16 look similar and share many parts, they are completely different in that the AR-15 operates as a semi-automatic only. This means you pull the trigger one time, only one round is fired. No different than any other semi-automatic rifle or handgun. The M-16 on the other hand is capable of fully automatic fire. This means you pull the trigger one time and the rifle continues to fire until you let go of the trigger or you run out of bullets.
The AR-15 has become the most popular sporting rifle in America. One reason for it’s success is the modularity of the platform. You can customize it for any number of tasks, then in a matter of seconds or minutes, you can reconfigure it into a new configuration to better suit the task at hand.