India, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine, commonly known as HMX (High Melting Explosive), is manufactured by the modified Bachmann combination method using continuous nitrolysis of hexamine in a cascade of four stirred tank reactors. In this laboratory, the technology was established more than three decades ago with all overall yield of about 40%. However, as the reported yield of HMX is around 55%, it was considered essential to systematically study the Bachmann reaction system to improve the yield. As such a detailed study on quantities/ratios of raw materials and process conditions was carried out to improve the yield. Optimized ratios of raw materials, use of nitric acid having strength >99%, proper control of temperature and optimal nitration and residence time gave an yield of 60-65%.