I don't know much about the .222, other than that it's supposed to be very accurate. The 223 has a bit more case capacity, if I'm not mistaken, and is a much more common round. I don't think you can buy 222 ammo anywhere near as cheap as you can the 223, either.

The 17 hmr is built around a 22 magnum case. I think the.17that came from the regular 22lr iscalled the 17 mach 1, but I'm notsure.Are you thinking about rebarreling your 22 rifle?