Abstract: In order to study the control of thecombustion stability of the bulk-loaded liquid propellant gun (BLPG), asimulating equipment of ignition and injection of the BLPG and four kinds ofstepped-wall chambers were designed. A high speed digital video system wasused to observe the expansion process of the energetic gas jet in a liquidsimulating medium. The congestion phenomenon in the experiment was analyzed.Results show that the jet expansion process in the stepped-wall chamberis stable and the injection pressure, the nozzle diameter and the stepped-wall geometryhave a remarkable influence on the jet expansion and the mixing process ofgas and liquid, so the jet expansion process can be controlled effectivelyby adjusting these parameters. The congestion of the nozzle causesdissymmetric jet expansion and affects the mixing process, so that it isunfavorable for controlling the jet stability.