One method of making metal tubes, especially high alloy tubes, is to centrifugally cast a cylindrical muff, and then reduce the muff in diameter and wall thickness to form a tube. Since considerable impurities or defects are trapped in the metal of the muff near both the inner and outer surfaces during the centrifugal casting, both the inner and outer surfaces are machined to remove these defects prior to the reducing action. Some of these impurities or defects run fairly deep into the wall thickness, and thus much machining is necessary to remove the defective material. One band of impurities or defects generally starts at the outer surface of the muff, about midway along its length, and progressively goes deeper, extending towards the non-pouring end of the muff or casting.