Out at the range today working on handloads for a new 300 WM (New model 70). All of my primers are cratered, from starting loads to a half grain below max as per the Speer manual. I blew 2 primers during all the fun. In speaking with a fellow out there he asked if I had the same problem with factory ammo to which I replied that I had never fired factory stuff in this particular rifle. He throws me a couple rounds that I fire and lo and behold....cratered primers. Any ideas as to what the problem may be?