An approximate numerical model of the Double Pipe Test has been devised to examine the effects of properties of the top pipe, witness pipe and the explosive on the depth of dent generated in the witness pipe. The model is based on a static calibration of the strength of the witness pipe, with strain-rate correction for high rates of loading. The inertia of all material accelerated by the explosive product gases is also considered. A comparison of predicted and measured dent depths for various peak explosive pressures shows that the model adequately describes dynamic behaviour during the test. Measured dent depths are expected to correlate with the ability of an explosive to generate a shock wave in rock.