The 6br guys say the combo it the cats meow! (But they use the small magnum 450 primers) I have never tried it with large mag primers, but Speer's manual says to use the magnum primers with ball powders like H380. Do you have 9 1/2 or 9 1/2M primers? The "M" primers are magnum. I have been told that the 7 1/2 primers are considered a magnum primers, and I have had good luck with them and varget.