I never used them on varmints but have worked up loads for predator hunting in my 22-204, 5.6x50R, 6x45mm and 6mm-204. They work just fine. I like the 55gr NBT Lead-Free's in the 6mms and 40 gr NBT Lead-Frees in the .224's. I did have problems with seriously large exits with the 62gr Varmint Grenades but they were accurate.
40gr NBT LF out of the 22-204. I've killed a number of coyotes with the 6mm and they work fine also.
Our state was talking about going lead-free so I got on the stick and was going to have ammo ready to go so I would be out hunting instead of sitting home knashing my teeth over the stupid new law. If it ever did happen I'd stay hunting.