.222

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As for the sub-calibers I don't see much about the .222 remington any more! It is the most accurate cartridge in the world next to the 6mm ppc, but is easy to load, shoots almost any bullet weight with many types of powders and there is loads of information on this round out there. Maybe shooters are just looking for something new or faster and don't care about accuracy, but if you are looking for a great caliber to experiment find a .222 and find out what it is like to shoot small groups. Good Luck