Gotta add my 2 cents worth. I was told magnum primers add 10 fps and were not that much different from standard. That has been my experience. I use them for my cowboy loads with Trail Boss and started using them with my 9mm loads with AA #7.
The 9mm uses a 147 grain molly bullet and the powder is 6.3 grains of AA #7. That is the
bottom of the range.
I need 835 fps.
The reason I use magnum Federal primers: They were the
only thing I could get last year that were Federal!
I need to use them up.
I have a stock of standard primers now. Along with S&W revolvers and a Glock that requires them for reliability.