A mathematical algorithm is described for cycle-wise simulation of locked-cycle grinding tests in a ball mill using multicomponent feeds. The simulation is in good agreement with extensive experimental data for quartzite and limestone mixture feeds ranging in composition from 1:3 to 3:1. The simulation model is employed for generating transients in the locked-cycle tests by imposing either relatively large step changes or random fluctuations in a narrow band width on the composition of the feed, its fineness and the grinding time. Because locked-cycle tests mimic closed-loop grinding circuits with plug flow transport through the mill, the simulation provides useful insight into the stability and control of industrial comminution circuits where ore composition and hardness and the feed rate are invariably subjected to minor fluctuations on a more or less continuous basis, and occasionally to rather abrupt large changes.