I've had a Vixen .222 for a long time and a very accurate varmint bullet has been the 50 grain Sierra Blitz or the regular high velocity version of the same bullet, especially with Reloder 7. This bullet is a good one in all the slow twist .22s including the .220 Swift. I realize components are hard to find and the 50 TNT is certainly worth trying. My notes show good accuracy with this bullet using Reloder 7; it didn't do so well with H4895 and IMR4198.
Look at some manuals. Lots of good .222 loads and you'll find this cartridge among the easiest to work with when it come to accuracy. I've never had much interest in bullets under 50 grains, but one of the few I've work with was the Sierra 45 grain. It will shoot about as well as the 50 grain.
