Rate of fire Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles . It is usually measured in rounds per minute ( RPM or round / min ) , or rounds per second ( RPS or round / s ) . Overview . Note that both generation of heat ( leading to weapon failure ) and exhaustion of the weapon ' s ammunition mean that most automatic weapons are unlikely ever to sustain their cyclic rate of fire for a full minute ; thus , it is technically incorrect and potentially misleading to describe RPM as " the number of rounds a weapon can fire in one minute . " For manually operated weapons such as bolt - action rifles or artillery pieces , the rate of fire is governed primarily by the training of the operator or crew , within some mechanical limitations . Rate of fire may also be affected by ergonomic factors . For rifles , ease - of - use features such as the design of the bolt or magazine release can affect the rate of fire . For artillery pieces , a gun on a towed mount can usually achieve a higher rate of fire than the same weapon mounted within the cramped confines of a tank or self - propelled gun . This is because the crew operating in the open can move more freely and can stack ammunition where it is most convenient . Inside a vehicle , ammunition storage may not be optimized for fast handling due to other design constraints , and crew movement may be constricted . For automatic weapons such as machine gun s , the rate of fire is primarily a mechanical property . For a third hybrid class of weapons , common in handguns and rifles , known as a Semi - automatic firearm , the rate of fire is primarily governed by the ability of the operator to actively pull the trigger . No other factors significantly contribute to the rate of fire . Generally , a semi - automatic firearm automatically chambers a round using blowback energy , but does not fire the new round until the trigger is released to a reset point and actively pulled again . Semi - automatics ' rate of fire is significantly different from and should not be confused with full - automatic s ' rate of fire . Many full - automatic small arms have a select - fire feature that allows them to be ' downgraded ' to semi - automatic mode by changing a switch , but the reverse is not true , semi - automatics do not have a full automatic mode without gunsmith - level modifications . Over time , weapons have attained higher rates of fire . A small infantry unit armed with modern assault rifles and machine guns can generate more firepower than much larger units equipped with older weapons . Over the past century , this increased firepower is due almost entirely to the higher rate of fire of modern weapons . A good past example of growth in rate of fire would be the enormous advantage of the Maxim machine gun , which provided accurate and steady fire . This was due to technological advances in the field of material cooling . Measurement . There are three standard measurements of rate of fire for automatic weapons : Cyclic rate . This is the mechanical rate of fire , or how fast the weapon " cycles " ( loads , locks , fires , unlocks , ejects ) . Measurement of the cyclic rate assumes that the weapon is being operated as fast as possible and does not consider operator tasks ( magazine changes , aiming , etc . ) . When the trigger is squeezed , the rate at which rounds are fired is the cyclic rate . Typical cyclic rates of fire are 460 – 900 RPM for assault rifles , 1 , 000 - 1 , 100 RPM in some cases , 900 - 1 , 200 RPM for submachine guns and machine pistols , and 600 - 1 , 200 RPM for machine guns . M134 Miniguns mounted on helicopters can achieve rates of fire of over 100 rounds per second ( 6 , 000 RPM ) . Sustained or Effective rate . This is the rate at which the weapon could reasonably be fired indefinitely without failing . In contrast to the cyclic rate , the sustained rate is the actual rate at which the weapon would typically be fired in combat . Sustained rate considers several factors , time spent reloading , aiming , changing barrels if necessary , and allowing for some cooling . Knowing the sustained rate of fire is useful to know for logistics and supply purposes . Machine guns are typically fired in short bursts rather than in long continuous streams of fire , although there are times when they must be fired in very long bursts ( see rapid rate below ) . Sustained rate also applies to box magazine fed assault rifles and semi - automatic rifles . In these weapons it refers to the rate at which the typical rifleman can effectively engage targets in a combat situation . The rate is usually 12 - 15 rpm , except for barrel changes it considers most of the same factors as for the belt fed MGs . Rapid rate . Rapid rate is a rate of fire between Cyclic and Sustained . It is usually much faster , although less accurate , than the sustained rate and is only used in emergency / final defensive line situations . The Rapid rate is not sustainable for long periods because it eats up a significant amount of ammunition ( more than the gunner or assistant gunner are likely to carry on a patrol ) , the heat generated requires barrel change times to be reduced , and because machine guns are only issued with one spare barrel prolonged rapid fire will result in shortened weapon / barrel life . The Neal submachine gun came with 5 barrels to overcome this problem . Semi - Automatic rate . The semi - automatic rate is the assault rifle / semi - auto only version on rapid fire . It is the maximum rate that a weapon can fire with any degree of accuracy in semi - auto mode , usually 45 - 60 rpm . However a semi - automatic firearm can mechanically function at ( about ) the same rate of fire as its fully automatic ( or select - fire ) counterpart , this is assuming the trigger could be pulled fast enough to facilitate such a rate of fire . Technical limitations . The major limitation in higher rates of fire arises due to the problem of heat . Even a manually operated rifle generates heat as rounds are fired . A machine gun builds up heat so rapidly that steps must be taken to prevent overheating . Solutions include making barrels heavier so that they heat up more slowly , making barrels rapidly replaceable by the crews , or using water jackets around the barrel to cool the weapon . A modern machine gun team will carry at least one spare barrel for their weapon , which can be swapped out within a few seconds by a trained crew . Problems with overheating can range from ammunition firing unintentionally ( cook - off ) , or , what is much worse in combat , failure to fire . Water - cooled weapons can achieve very high effective rates of fire ( approaching their cyclic rate ) but are very heavy and vulnerable to damage . A well - known example is the M1917 Browning machine gun heavy machine gun , produced in both . 30 - 06 Springfield version and . 50 BMG versions : the former weighed 38 kg ( 84 lb ) , while the latter weighed 66 kg ( 121 lb ) including coolant . Due to these disadvantages , water - cooled weapons have gradually been replaced by much lighter air - cooled weapons . For weapons mounted on aircraft , no cooling device is necessary due to the outside air cooling the weapon as the aircraft is moving . Consequently , aircraft - mounted machine guns , autocannon or miniguns can sustain fire far longer than ground - based counterparts , firing close to their cyclic rate of fire . Another factor influencing rate of fire is the supply of ammunition . At 50 RPS , a five - second burst from the M134 would use approximately 2 . 5 kg ( 5 . 5 lb ) of 7 . 62 mm ammunition ; this alone would make it an impractical weapon for infantry who have to carry a reasonable supply of ammunition with them . For this and other reasons , weapons with such high rates of fire are typically only found on vehicles or fixed emplacements .