We have used a ’’reverse gun’’ that fires a ceramic plate at a preheated metal target to study the dependence of flow stress on temperature. Impact velocity versusLf /L0isotherms have been determined for Al, two types of Cu, 4340 steel, and Ta at 295, 730, and 1235 K, and for U at 295 and 725 K. A modified Steinberg–Guinan constitutive model and a Gru¨neisen equation of state were used to obtain hydrodynamic code simulations of the deformation process. A strong temperature dependence of the length ratio was clearly evident for all materials.