Pressure will raise slightly with the magnum primer but i wouldn't worry at all about pressure with the charge weight and powder you're using. If you were already using Winchester LP primers you really won't see a difference in loads using a CCI LPM primer instead.

Like said above, a magnum primer isn't necessary with the powder you're using but you already know that. Not to worry in the application you're using.

__________________
Freedom is never free!!
SWCA #3437