Some examples are below.
Burst fire; http://vocaroo.com/i/s1nEy5u48O3l
Single fire; http://vocaroo.com/i/s0faFKzcr1Ye
All of these sounds were taken from military battlefields for more accuracy. They where taken by the U.S. military or Department of Defense during the course of the person’s official duties. Under United States copyright law, they are public domain (or so i guess).