You might want to start paying strict attention to what and how you are doing. Reloading is one of those things where the details matter. Some details matter a lot.
Don't load maximum charges of powder with the magnum primed cases, just to be on the safe side , use a charge between starting and maximum and you will be fine.
You can deprime those primed cases , just do it slowly , wear hearing protection . I've deprimed a lot of primed cases and even reused the primers with no problems. Do it slowly !
Gary