you mean from civilians? they can ask them all to re-apply for permits.
in some places, they have urged people to hand them in, and it worked.
in other places, they got paid or got tax reduction.
as for confiscating guns from criminals, they already do.
and then this is should be done
http://t0.gstatic.com/images?q=tbn:q.../armas.jpg&t=1