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Yes it is different with magnum loads and you will have to work up your loads again for the different primer. Don't know this from personal experience but from reading on here and from friends who have done what yoy want to do.
I've been burning off several thousand Win LRM primers I recieved by mistake until I go back to regular Win LR with no ill effect or noticable difference in normal cases like .308/30-06/.45-70 etc.