Re: .223 for general varminting
I shoot a Winchester HV70 .223 26" barrel, topped with a Zeiss Conquest 4.5-14 scope.
I also have shot a lot of prairie dogs with a "self-custom built" ar15 (.223), DPMS components. 20" stainless bull barrel 1:9 twist, hard chromed bolt group. Incredible accuracy from this rifle.
My favorite varmint bullets are Barnes varminators, 50 & 60 grains.