Magnum primers substitution

[L. Cooper]

The result will be changes in pressure. Most likely, but not certainly, there would be a higher peak pressure.

The only safe way to substitute ANY new component into a load is to start with a low pressure load and work up to toward maximum.

Some people believe that magnum primers are better for loads that will be used in extreme cold. Only testing will prove anything for your specific loads (which you don't describe at all). I use the same magnum primers with any data for any cartridge from any manual that used magnum primers in their tests to arrive at that data.