It's not the primers. I use small pistol primers in my 300 BLK sub loads. It's most likely the bullets. I've had the same issues with the Hoosier bullets going into my chamber. I've had to mortar the rifle to get them to eject. Once ejected, I fed them through a friends SOLGW and it fed just fine. Tight chamber? Possibly... What upper are you running?After reading this article, I still come away without a clear reason to use magnum primers in 300 blackout. The amount of powder (especially in subs) hardly requires a magnum primer. I understand that the load data calls for it, and that may be reason enough to use it I suppose.