Complex sentence: But Moller's guns, which had advanced with the infantry, tore gaps in the closed French masses, and when the French columns arrived within effective musketry range, the attack died out before the rapid and methodical volleys of the Prussian line.
Split into simpler sentences: But Moller's guns, which had advanced with the infantry, tore gaps in the closed French masses. When the French columns arrived within effective musketry range, the attack died out before the rapid and methodical volleys of the Prussian line.