We study the changes in groove shape and depth that occur when holographic gratings are replicated in plastic. Specifically, we measure the groove profiles and spatial frequencies of electroplated metal shims made from sinusoidal holographic gratings, and also the same properties of the replicas made of polymethylmethacrylate (also metal shims). Nine samples are studied that have spatial frequencies in the range 600 to 2000 mm-1. The shims of the replicated gratings have up to 30% shallower grooves and 13% lower diffraction efficiencies than the shims of the originals. The maximum measured diffraction efficiency for shims of the original gratings having 525-to 620-mm-1 spatial frequencies correspond to a 0.22-μm groove depth, which agrees with the calculated value. We use this information to modify the groove shapes on the holographic gratings to make better plastic replicas.