I have a friend I shoot ground squirrels with, although he is using a custom Martini single shot in .219 Zipper (32 gr h2o capacity cases) it should be pretty close to your .222. He uses an Accurate Molds LLC, spec'd for his throat, .002" over groove dia, true bore riding nose section, small flatnose, plain square base, 60 ish gr wheelweight at around 1450 I think. That combo is benchrest accurate. I would think that would work well in your .222.
Maybe Gnoahhh will contribute here.
