[Chainsaw.]

I've heard.....take that for what it is, that mag pistol primers add about .01 to .02 grains of powder charge. So, if the starting load if 4.5 Id go say, 4.2. Mag primers are not dynamite, you'll survive. And keep in mind backing off to much can be bad news bears, usually its safe with pistol powders, notvso much with slow rifle powders, just fyi.