The seeding of a magnetocumulative generator (MCG) by a new type of ultracompact (25 cm³ in volume) explosive-driven source of primary power has been studied experimentally together with comprehensive computer simulation. The operation of the primary power source is based on transverse shock wave demagnetization of Nd₂Fe₁₄B high-energy hard ferromagnets. The use of the design of the shock wave ferromagnetic generator (FMG) with energy-carrying element made as a hollow Nd₂Fe₁₄B cylinder magnetized along the axis has made it possible to reduce dramatically (to 0.6 g) the mass of the high explosive (C-4) necessary for the operation of the generator with an Nd₂Fe₁₄B energy-carrying element of mass 185.7 g. The FMG is capable of producing in the coaxial seeding coil of MCG a seed current with peak amplitude exceeding four kiloamperes and full width at half maximum of several tens of microseconds. The methodology was developed for digital simulation of the seeding processes in the combined FMG/MCG system. Experimental results obtained are in a good agreement with results of digital calculations performed.