Primers are sometimes a matter of opinion, sometimes a matter of availability. I use CCI, Winchester, Federal and occasionally Remington. For the 7 mag you will want to use a large rifle magnum primer. All of the above make mag primers. The .270 also takes large rifle primers but "may" not need the magnums. You can use the mag primers in the .270 as long as you work up the load using these primers. That way you can stock one type of primer.
Never substitute components w/o re-working the load. Magnum primers will have a hotter flame and raise pressures (at least change the pressure curve). So you must not replace one type with the other or even switch between brands as each has it's own characteristics that must be accounted for.
For colder climates and or the use of ball type powders, a magnum primer will give better ignition and more consistent results.
