Selective fire A selective fire firearm has at least one semi – automatic and one automatic mode , which is activated by means of a selector which varies depending on the weapon ' s design . Some selective fire weapons utilize burst fire mechanisms to limit the maximum number of shots fired automatically in this mode . The most common limits are two or three rounds per trigger pull . Fully automatic fire refers to the ability for a rifle to fire continuously until the magazine is empty . " Burst - capable " fire refers to the ability of a rifle to fire a small yet fixed multiple number of rounds with one trigger pull . Semi - automatic refers to the ability to fire one round per trigger pull . The presence of selective fire modes on assault rifle s permits more efficient use of rounds to be fired for specific needs , versus having a single mode of operation , such as fully automatic , thereby conserving ammunition while maximizing on - target accuracy and effectiveness . Design . Selective fire weapons , by definition , have a semi - automatic mode , where the weapon automatically reloads the chamber after each fired round , but requires the trigger be released and pulled again before firing the next round . This allows for rapid and ( in theory ) aimed fire . In some weapons , the selection is between different rates of automatic fire and / or varying burst limiters . The selection is often by a small rotating switch often integrated with the safety catch or a switch separate from the safety , as in the British SA80 family . Another method is a weighted trigger , such as the Steyr AUG , which will fire a single shot when 8 . 8 – 15 . 4 pounds of weight is exerted on the trigger , and then become fully automatic when over 15 . 4 pounds of weight is applied . This is useful for emergency situations where a rapid volley of rounds is more effective for suppressing a close enemy rather than a single round burst . Some selective fire weapons offer a burst mode as the second option , where each pull of the trigger automatically fires a predetermined number of rounds ( generally two or three ) , but won ' t fire any more until the trigger is pulled again . The current U . S . standard assault rifle , the M16A4 , and the M4 carbine variant of this rifle fire a maximum of three rounds with each pull of the trigger in burst mode . In this design , it retains the count of previously fired rounds and may fire fewer than three rounds . Other designs reset the count with each trigger pull allowing a uniform three round burst as long as rounds remain . A common version of the Heckler & Koch MP5 submachine gun ( widely used by SWAT teams and military special operations personnel ) fires single shots , three - round - bursts , and automatically . A special variant uses a two - round - burst to minimize the chances of missing with a third round . Some automatic cannons have larger burst limiters to coincide with higher rates of fire . Selective fire weapons are regulated in the United States under the National Firearms Act of 1934 ; their new manufacture for the civilian market was prohibited by the Firearm Owners Protection Act of 1986 . Those still in circulation often command prices significantly higher than similar models still available to law enforcement and military agencies .