It has been demonstrated that the performance of direct-fire kinetic-energy ammunition improves significantly with increasing preignition temperature (approximately 5% performance increase at 49 degreesC above that demonstrated at ambient temperature for JA2). Existing launch systems are designed to withstand pressures up to the level generated by ammunition with a propellant temperature of 49 degreesC, but are typically used at lower temperatures. This study simulated the effects of heating the propellant bed of large-caliber ammunition to 49 degreesC by microwave energy. When rapidly heated, propellant within a propellant bed may not have sufficient time to thermally equilibrate. This study investigated heating a typical propellant bed in two configurations: (1) through heating one-half of the axial length of the bed and (2) radial heating into the bed along the entire axial length. A subscale (7.6 cm diameter) simulator was used. Pressure-time histories from several transducers placed along the wall of the simulator in the axial direction were used to elucidate the flame spreading process. Baseline tests of the propellant bed were conducted at -30 degreesC and at 49 degreesC. Tests of propellant beds with regions of both -30 degreesC and 49 degreesC simultaneously within the bed showed ignition and early burning characteristics approximating those at 49 degreesC.