I use Rem 9 1/2 mag primers in all of my rifles from .243 to 450-400. It is the most accurate primer in my 243 win and provides the least load to load velocity variation. IMHO I find that by using one primer all the time allows me better to read pressure (danger)signs as brand to brand primer cup hardness varies and some flatten easier than others. I find federal 210s will flatter more than Rem 9 1/2s with the same load. In the December Handloader there is an article by Gary Sciuchetti on the effects of various components in working up a 308 load. In this article a table gives the effect on accuracy only of various primers with all other components being the same. A pity that loads were not chronographed. There is also a table on Brass endurance with some cases giving up after 11 shots and others lasting until 24 shots after being full lengthed every shot. It gives food for thought.