I was out shooting my .260ai yesterday & noticed that exact loads using RP 9 1/2 primers vs Fed. 210 match, showed the RP primers giving a lower SD & slightly better accuracy in every load I shot. Anyone have a sim. exp. using RP 9 1/2 primers?

I have. Depends on the rifle. I tore my hair out with a 338 Jamison that wouldn't group consistently. I generally prefer Federal and Winchester primers and do very little with Remington and CCI. When I tried the 9½M Remingtons the groups tightened up significantly and the SD went way down. That gun just prefers Remington, and with most powder/bullet combos. Just today I was trying primers on some loads I've just about wound up. Turns out CCI 250's did much the same thing in a 323WSM as the 9½M's did in the other with one particular bullet. Primers DO make a difference about 25% of the time for me.

Match means more consistant. In your case, consistantly bad. That's the way things work out sometimes and why handloading can be a neverending hobby.

kinda goes back to trial and error, sort of what handloading is about. It also reminds me of when mike walker brought out the 17 rem. He said then that in loading the round use only rem 7 1/2 primers, that it isn't a ply to buy their primers, but in their testing it was the most constant ignition and gave by far the best accuracy.