RE: the most accurate cartridge
I tend to support the .30 caliber as being intrinsically accurate. The military has used it for many years, both by snipers in combat and for competition. I have two 308 Win's that will shoot a 5 shot single ragged hole at 100, and will consistently shoot under 2 inches at 200. I also have a 300 Win mag that will do the same if not better. I also have a 223 that will do the same thing.
However, the subject of accuracy must take in many details: action, barrel, stock, sighting system, proper assembly, and load development. But the most important part of the equation is the skill of the operator.
This is always a fun topic. Let's keep it going.
SD Shooter