  The model of a radial minor merger proposed by Quinn (1984), which
successfully reproduces the observed regular shell systems in shell galaxies,
is ideal for a test-particle simulation. We compare such a simulation with a
self-consistent one. They agree very well in positions of the first generation
of shells but potentially important effects -- dynamical friction and gradual
decay of the dwarf galaxy -- are not present in the test-particle model,
therefore we look for a proper way to include them.
