If you enjoy experimenting in search of the best accuracy, shooting groups with different primers is sometimes worth the effort. I've recently been experimenting with CCI-400s, CCI-450s, and Remington 7 1/2s in .222s and .223s (including ARs). Almost always there is a measurable but small difference, but you have to shoot several groups to know for sure.
I realize CCI-450 and Remington 7 1/2 primers are often recommended for ARs in .223 / 5.56, but generally, the smallest groups for me have been with CCI-400s. However, CCi-450s and Remington 7 1/2s are often very close. Splitting hairs, maybe, but that's the part some enjoy.
