Some other small-rifle primers aren't recommended for higher-pressure rounds, including the Remington 6-1/2. I describe the history and reasons behind all this in my new handloading book, but thought posting a caution here would also be a good idea.
I know what you mean about the 6-1/2s. I was using 7-1/2s in my .222, but switched to the sixes after reading Pet Loads, even though Ken's update used the sevens. Backed 1/2 grain off my powder charge to keep the primers looking pretty after firing. May have picked up a tenth or two in accuracy, maybe not. But, I've got a brick to go through, and minute-of-Coffeemate-bottle at 300 meters is fine for me.
