  We numerically investigate atomic interferometry based on spin-exchange
collisions in $F=1$ spinor Bose-Einstein condensates in the regime of long
evolution times $t\gg h/c$, where c is the spin-dependent interaction energy.
We show that the sensitivity of spin-mixing interferometry can be enhanced by
using classically seeded initial states with a small population prepared in the
$m_F=\pm1$ states.
