Changing primer's was never a problem with me. What ever difference they made didn't seem to amount to much so long as I used the same primer's in every bunch I loaded. But one time I did some experimenting as I have a ton of old Herter primer's. Made up some loads the same with one brand primer and then with Herter from the same box of case's. Herter primer's out shot the other's by a good bit. I think they were either Winchester or CCI primer's. BTW, even the other primer's gave me group's I could live with easily!