I saw basically negligible difference in std vs mag primers in the testing I did with my 270. You have to actually shoot the gun and components in question to know for sure though.
JMHO
Tim

"The significant problems we face cannot be solved at the same level of thinking we were at when we created them."
Albert Einstein

At Khe Sanh a sign read "For those who fight for it, life has a flavor the protected never knew".