17HMR is capable of tiny groups at 100 yards but it depends on lots of stuff. The three HMRs I have all work best with the 17 grain bullets, but some do well with the 20. Group size varies with brand of ammo, and even batch. And the little pill gets pushed around lots with the wind, so it requires a more careful shooter than larger rounds.
Poor answer I know, but I need more information about what you are going to do with it, and what you are planning to shoot it out of. Then maybe you will get a better answer.