when to fire back

[Smersh]

this is related "when to fire" question. . I usually have my machine guns fire around 500-600 meters from the enemy in support of infantry squads. since infanty combat seems to be more deadly compared to mbt, enemy squads tend to kill my mg crews by rifle fire from around 500m. am I just too close to the enemy, when firing? how far away should an mg be to be safe and still effective? too me 500-600meters is the limit.