I have never squirrel hunted with a .17hmr. I was just speaking from my experience shooting targets with a Stevens 310 I used to own. The CCI 17 grain hollow points I was using were very, very accurate when there was no wind, but all over the place at a light breeze. I would imagine the 20 grainers do better in the wind. I wasnt knocking the .17hmr by any means.
I can do all things through Christ which strengtheneth me. -Philippians 4:13 (KJV)