Starline 357 Magnum Brass Cases 357 Mag Brass (Magnum Small Pistol primer)357 Magnum Brass, 357 Mag Brass, 357 Brass, 357 Smith & Wesson Mag Brass, 357 S&W Mag Brass, .357 Mag Brass1.275 - 1.285 O.A.L. 357 Mag Brass: Basically a lengthened version of the .38 special, the 357 Magnum is one of the most popular handgun calibers in the world. Almost every revolver manufacturer makes a firearm in this chambering. Also used in many lever action carbines. 357 Magnum Brass. 100 count by weight