First of all, welcome to THR.
As a general rule, using magnum primers requires a small reduction in charge weight compared to a load using standard primers, and some spherical powders just specify magnum primers by default.
Please don’t take offense but the wording of your question makes me a little concerned that you don’t understand that there are dozens of different varieties of powder, and that only some of them are suitable for your particular cartridge. How much powder you use depend entirely on what brand and variety of powder it is. You really need to consult a reliable source of reloading data and follow their recommendation. You might start here:
https://www.hodgdonreloading.com/data/rifle