An oscillating cooled mold assembly for the continuous, high-speed casting of metallic strands or rods, especially upcasting strands or rods of copper alloys such as brass, has a hollow die in fluid communication with a melt typically held in a casting furnace. A cooler body surrounds the die in a tight-fitting relationship to form a solidification front in the melt as it advances through the casting zone of the die. The strand or rod formed from the solidified melt is pulled through the die while the mold oscillates in a direction substantially parallel to the direction of travel of the rod.