The initial run of 500 S&W Mag (R) cases was built to use large pistol primer per Smith & Wesson and Cor-bon specifications. On July 28, 2003, Smith & Wesson and Cor-bon changed specification of primer pocket to be large rifle. Rifle primers are the same diameter as pistol except they are approximately .006" taller. This was done to prevent the primer from being pierced by firing pin when loaded with max loads and heavy bullets (bullets over 400 grains). It was determined that hole in the primer allowed pressure to damage firing pin and bushing, kind of like a cutting torch and the harder cup of a rifle primer will prevent this occurrence.
All cases sold by Starline, Inc. after July 28, 2003, feature a large rifle primer pocket to accept a large rifle primer. Hodgdon Powder has generated load data which recommends using Winchester large rifle primers. Click here to view or call 918-251-5640. Cor-bon has also tested and recommends CCI 250 primers (Magnum Large Rifle).
Our new cases will have an "R" after the "Mag" on head stamp to signify rifle pocket. If you have previously purchased 500 cases without "R" on head stamp and wish to modify, you can use a large rifle pocket uniformer to deepen primer pocket to accept large rifle primers by deepening pocket approximately .006". This will not affect the integrity of the case.
For concerns regarding this situation contact Smith & Wesson or Cor-bon as they designed the case and subsequently changed it.