The internal shape of planetary ball mill jars was modified to increase the efficiency of the milling process. Four new jar designs are presented, where obstacles on the surface of a traditional cylindrical jar modify the ratio of normal-to-tangential transferred mechanical action, thus improving the comminution of the mill charge and reducing the process time. Multibody dynamics simulations, validated by operando video recordings of the process, were employed to investigate modified ball motion regimes promoting the increase of the number of high-energy impacts. Moreover, experimental grinding of calcium fluoride powder was performed to assess the effect of milling time and jar-to-plate velocity ratio, through the evaluation of size and microstrain of the end product deduced from X-ray diffraction line profile analysis. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.