Since all the gunpowder, bullets, arms, and making machinery in the Kagoshima arsenal had been constructed or purchased with the money contributed by the then retainers of the Satsuma Domain, the former retainers took it for granted that these things were to be used by the retainers and their descendants in an emergency; therefore, because the Shigakko students got angry with the central government for carrying the domain's property out from there like a thief and for the purpose of being prepared with arms and ammunition for a possible conflict with the central government, they made a night attack on the powder house at Somuta and seized bullets and arms.
また、旧薩摩藩士の心情として、鹿児島属廠の火薬・弾丸・武器・製造機械類は藩士が醵出した金で造ったり購入したりしたもので、一朝事があって必要な場合、藩士やその子孫が使用するものであると考えられていた事もあり、私学校徒は中央政府が泥棒のように薩摩の財産を搬出した事に怒るとともに、当然予想される衝突に備えて武器・弾薬を入手するために、夜、草牟田火薬庫を襲って弾丸・武器類を奪取した。