In the really big magnums, i.e., like the 378 and 460 Weatherby Magnums I only use Federal 215 primers. For my 7mm Remington Magnum loads, I use Federal 210M primers. I use magnum primers for 257 & 300 Weathery Magnum loads, for 300 Win. Mag. loads & 458 Lot loads but I probably wouldn't need...