This paper is concerned with methods to determine the resultant impact load pulse on test structures during gas gun tests. The muzzle of a gas gun carries an instrumented target support designed to measure force-time-pulses of the impact event on structures mounted on the device. The target during impact is supported on two long slender metallic bars with axial strain gauges. By measuring the impact strain pulses in the support bars and assuming longitudinal wave propagation, it is possible to determine the impact load pulse on the target. The paper describes the strain measuring device and methods for determining the impact loads during impact. Gas gun test results with different projectiles are presented and the load pulses compared with a direct load measurement from a target load cell. The paper discusses possibilities and limitations of the device for quantitative force pulse measurements.