Abstract: The influence of pressure gauges to the reaction flow field is studiedexperimentally. Pressure histories during the shock initiation process for amodified double based propellant is measured with enhanced accuracy. A newreaction rate equation for modified double based propellant is proposed, andthe coefficients in the equation are calibrated on the basis of a globalcalibration method. The shock initiation process is also simulated for thepropellant, and the results show that the calculation agrees well with themeasured histories.