In this study, a scientific investigation was conducted to diagnose the conservation condition and establish an appropriate conservation treatment plans prior to comprehensive conservation treatment o f the B ullanggi J apo, t reasure which is c onsidered a valuable r esource in t he h istory o f firearms development. Morphological surveys, radiographic surveys, 3D scans, and color difference analysis confirmed the form and conservation status of the Bullanggi Japo, and it was judged that a conservation treatment method involving complete removal of the coating materials used in the past and the application of impregnation is required. In particular, it was found that sufficient reaction time should be set for each process to meet the requirements such as the size and weight, internal density, defects, etc. of the Bullanggi Japo, and care should be taken to consider vulnerabilities. In addition, P-XRF, XRD, and FT-IR analyses confirmed the composition and surface contamination, and identified that the Bullanggi Japo is composed of Cu-Sn-Pb and various corrosion products on the surface is attributed to internal alloying elements. Partly due to the presence of pitting corrosion products that erode the interior, it was determined that the conservation treatment is needed to inhibit the activity of these internal corrosive factors and eliminate potential factors to provide stability. Based on the results of the previous scientific investigations, the conservation treatment was carried out in the following order: surface decontamination - stabilization treatment - consolidation - restoration – survey after conservation treatment and finishing. In each process, color difference and glossiness were measured to understand the changes, and through a comprehensive review of the various findings, it was confirmed that they are suitable for use as indicators of conservation treatment.