Cheap/bulk CCI Blasers (anything CCI except "CB or Quiet"), Federal Champions, AE work well. Usually solid, round nosed ammo. Mine did actually like Remington sub-sonic, and shot well with it. Mine tend to not like Winchester ammo (555, etc). Another poster on here had the opposite experience, and his 64 loved winchester bulk.
I adore the 64, but they can be finicky eaters. Test a few different kinds, and keep a note of what cycled best in yours. Keep the action dry, and lube only for rust prevention/storage. Clean every 500-1000 rds.