<P> 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 pulled, the rate at which rounds are fired is the cyclic rate . Typical cyclic rates of fire are 600--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 attack helicopters and other combat vehicles can achieve rates of fire of over 100 rounds per second (6,000 RPM). Cyclic rate of fire is the only rate that can be determined scientifically . </P> <P> 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 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 . </P> <P> 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 great amount of ammunition (more than the troops are likely to carry on a patrol), the heat generated requires barrel change times to be reduced, and with the one spare barrel usually issued, prolonged rapid fire will result in shortened weapon / barrel life . </P> <P> 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 or explosion of the weapon . </P>

How many rounds per minute can a fully automatic rifle shoot