There are precautions to take with primers, some carts it don't matter if you use either large rifle or large rifle mag, but some are particular, due to the way the powder needs to be burnt, changes pressures at times as well, your best bet is follow the powder manual, when the manual states large rifle, it means only large rifle primer, unless indicated that you should use a mag primers, many times edging to the max or compressed load the book will indicate to use mag primers, using the mag primers help burn the powder completely. Some reloaders step up to mag primers using curtain carts, due to the climates they hunt, generally cold weather climates. they do this for better ignition. Aim small hit small. RAMbo.