The paper presents results of the experimental study of the impact of the weak magnetic field in the sensibility of the powder of ammine cobalt perchlorate to the action of the nanosecond-durability high-current electron beam (HCEB). The powder of ammine cobalt perchlorate of two types of dispersity, coarse particles and microparticles, was utilized in our study. We discovered that both weak magnetic field and powder dispersity have a strong impact on the sensibility to the effect of the HCEB.