<P> The M276 is a violet - tipped 7.62 × 51mm NATO dim tracer that uses composition R 440, which is barium peroxide, strontium peroxide, calcium resinate for example calcium abietate, and magnesium carbonate . </P> <P> Tracer compositions can also emit primarily in infrared, for use with night - vision devices . An example composition is boron, potassium perchlorate, sodium salicylate, iron carbonate or magnesium carbonate (as combustion retardant), and binder . Many variants exist . </P> <P> Tracers can also serve to direct fire at a given target, because it is visible to other combatants . The disadvantage is that they betray the gunner's position; the tracer path leads back to its source . To make it more difficult for an enemy to do this, most modern tracers have a delay element, which results in the trace becoming visible some distance from the muzzle . Depending on the target, tracer bullet lethality may be similar to standard ball ammunition . The forward portion of a tracer bullet contains a substantial slug of lead filler, nearly as much as the non-tracer ball round that it trajectory matches . In the case of the M196 / M193 bullet set, the lethality differences are probably negligible for this reason . However, with the M856 / M855 bullet set, the M855 ball round contains a steel penetrator tip that is not present in the M856 tracer bullet . As a result, different lethality effects can be expected against various targets . Nevertheless, under some circumstances, a slight degradation in lethality can often be made up for by the psychological and suppressive - fire effects tracer bullets can have on an enemy who is receiving them . </P> <P> Besides guiding the shooter's direction of fire, tracer rounds can also be loaded at the end of a magazine to alert the shooter that the magazine is almost empty . This is particularly useful in weapons that do not lock the bolt back when empty (such as the AK - 47). During World War II, the Soviet Air Force also used this practice for aircraft machine guns . One disadvantage in this practice is that the enemy is alerted that the pilot or shooter is low on ammunition and possibly vulnerable . For ground forces, this generally offers no tactical advantage to the enemy, since a soldier with a crew - served weapon such as a machine gun who is out of ammunition is supposed to alert his team that he is "dry" and rely on their cover fire while he reloads the machine gun . Thus, an enemy must risk exposing himself in order to attack the reloading soldier . Modern jet fighters primarily rely on radar and infrared seeker missiles to track and destroy enemy planes and laser - guided missiles to attack surface targets, rather than the plane's cannon, which may be just an ancillary weapon for air - to - air combat; although in the ground attack role, cannon fire may be emphasized . However, modern fighter aircraft use gyroscopes and inertial sensors coupled with radar and optical computing gunsights that make the use of tracers in cannon ammunition unnecessary . As long as the pilot can put the "pipper" (aiming point) in the HUD (head - up - display) onto the target, he can be assured that the burst will be on target, since the computers automatically compute range, closing rate, deflection, lateral accelerations, even weather conditions to calculate target lead and aimpoint . Thus one of the primary reasons for using tracers on aircraft in the first place, uncertainty over where the bullets will end up in relation to the target, is removed . Another use for the tracer is in tank hull machineguns, of mostly out - dated tanks, where the machinegun operator cannot sight directly along the barrel, thus he has to rely on tracer bullets to guide his aim . Modern main battle tanks and armored fighting vehicles, however, employ advanced fire control systems that can accurately aim secondary weapons along with the main armament; although the continued use of tracers provides reassurance to gunners on the direction of machinegun fire . </P>

Why did soldiers need to make their own bullets