Abstract Forces exerted by the load on the liner in both a dry mill (no ore present) and a wet mill (containing ceramic media and a silica slurry) were measured. The conductivity between a probe and the liner was also measured in the case of the wet mill. In the dry mill it was found that with a relatively rough wave liner the load behaviour changed markedly for mill speeds above 77% of critical speed, exhibiting a tendency to centrifuge as mill speeds exceed 100%. For the smooth liner minimal change in the force profile occurred because of slip between liner and load. In the wet mill the analysis of the force and conductivity profiles provided a coherent picture of load behaviour as speed increased for load volume J = 35% and slurry composition 67.5% solids by mass. Although the liner in the wet mill was relatively rough (simulating the grid liners used in industrial mills) there was substantial slip between the load and the liner, with no evidence of premature centrifuging of the load even at high mill speeds (eg 100% of critical speed).