The RSDS of the 300-kg and 700-kg batches from each step of mixing are plotted in Figs. 7 and 8, respectively. Although there is a decrease in RSDS from blend 1 to blend 2 at each sampling location in the powder bed, the degree of micro-scale mixing in the comilling step at large scales is not as effective as that observed at the 20-kg scale. This is demonstrated by the wide range of RSDs observed for blend 2 after comilling, i.e., 2.7%–10.5% for the 300-kg scale and 4.8%–15.1% for the 750-kg scale. The corresponding range on the three 20-kg scale batches is much narrower, 0.8%–4.7%. The noticeable impact from scale up in micro-scale mixing delivered by comilling is likely due to the change in the size of the comil causing a difference in the residence time and working volume of the powder in the chamber.