I bought 1000 223 cases from Rocky Mountain Reloading, They are said to be salvaged new cases, primed, with the bullets and powder pulled. My question is on Neck sizing. They say to neck size first, but since they are primed I have removed the rod from the Lee Neck Collet Sizing Die. Before any sizing attempt, a flat based bullet will hardly even fit into the neck, and the neck collet die makes them really too small. Should I just load and go? Plan to shoot in a S&W M&P 15.