Selective fire, or "select fire", means the capability of a weapon's fire control to be adjusted in either semi-automatic, fully automatic firing modes, or 3 round burst. The modes are chosen by means of a selector, which varies depending on the weapon's design. Some selective-fire weapons have burst fire mechanisms built in to limit the maximum number of shots fired in fully automatic mode, with most common limits being two or three rounds per trigger pull. The presence of selective-fire modes on firearms allows more efficient use of ammunition for specific tactical needs, either precision-aimed or suppressive fire. This capability is most commonly found on military weapons of the 20th and 21st centuries, most notably the assault rifles.