[rgraham]

The M16 has been semi-auto (single fire and three round bursts) since the Vietnam war with the rare exception of special forces weapons[1]. Fully automatic mainline rifles are inaccurate, wasteful, expensive, and less effective.

[1] http://en.wikipedia.org/wiki/M16_rifle#M16A2

[pionar]

Burst fire IS semi-auto, despite the other commenter. Automatic firing means that when you hold down the trigger it continues to fire until either the trigger is released or the ammunition supply is exhausted.

[DennisP]

The federal government does not consider burst to be semi-auto. Semi-auto rifles are legal for civilians without any special license. Automatic weapons require a Class III license and no civilian can buy one manufactured after 1986. Three-round burst falls into the later category, and any gun store in the U.S. will use the same terminology as the ATF.

[pionar]

I've been in many gun shops, never heard them referred to as automatic weapons. At least in the midwest, I've heard them referred to as either "burst" or Class III weapons.

[chloraphil]

Burst fire is NOT semi-auto.