Yup. Magnum primers are only for magnum rounds, and you don't want to screw up on this. (Particularly with Blue Dot!!)9mm and 38 Spl take normal primers, and the 357 takes magnum. Even hot 10mm loads use regular primers, and Blue Dot is THE powder of choice for 10mm. 45, 45 Super, 40, and 50 GI all ...