The paper is devoted to determining the acceleration of test items on shock stands. To form the required laws of motion between the striker and the bench table, shims of different thickness with different nonlinear loading characteristics are installed. The acceleration of the table with a test item is determined by the elastic and inertial properties of colliding bodies, the nonlinearity of the shims and the superposition of incident and reflected waves. The paper proposes to perform the calculation of table acceleration in two stages. At the first stage, the slow component of the acceleration of the longitudinal motion of the instrument table should be determined by considering the nonlinear elastic collision of absolutely solid bodies. At the second stage, the fast component of the acceleration is calculated as a result of summing up the incident and reflected waves. A homogeneous rod is taken as a dynamic model of the table.