Cartridge Brass Manufacturing Process – How Cases Are Made

Lapua, Norma Peterson or RWS are the preferred brands of brass for precision benchrest and F-class shooters. (Lake City makes quality brass for military calibers. Premium brass is more accurate, has more consistent velocity, and lasts longer. Many shooters know the importance of brass, but don’t know how cartridge cases are made. Here’s a look at how cartridge cases are made. Top Deep-Draw Illustration of a Ram from Demsey Mfg. The process begins with a brass disc stamped from metal strips. The brass is then extruded into a cylindrical form through a series stages. The brass is pressed through a die at high pressure during the extrusion procedure. This process is usually repeated two or three more times. In the traditional “draw” method, the case is stretched in three to five stages using high-pressure rams that force the brass into a die. RWS, a company that produces some of the most uniformly-sized brass in the world, uses the draw method. “It begins with cup drawing, after the bands have already been punched.” RWS cases are drawn three times and are then annealed and pickled and rinsed. They are also subjected to quality improvement measures. This results in a specific hardening and increase of the brass cases’ resistance to extreme stresses. FYI, Lapua uses a traditional drawing process to manufacture most cartridge brass. After the cases have been extruded or drew to maximum length, they are trimmed and neck/shoulder formed. The extractor groove is then formed or machinized (on rimless case) and the primer pocket in the base is created. A “bunter” is a hardened steel plug that can be used to form the primer pockets. The photos below show the stages of forming a cannon case (20mm) (courtesy OldAmmo.com), as well as bunters used to form Lake City rifle brass. This shows the draw process, as opposed to extrusion. The process for drawing-forming rifle brass is the same as that of this 20mm shell. It’s just smaller. River Valley Ordnance explains that when a case is made, it’s drawn to its final length with a diameter slightly smaller than required. The head of the draw has a slight rounding and no primer is required at this stage. The final drawn cases will be trimmed and then run through the head bunter. A punch ground to the intended contours of the inside of the cases pushes the drawn into a cylindrical case and holds it in position while another punch rams the case from the opposite end, slamming the bottom flat. This secondary ram holds a headstamp bunter pun. This video uses DEFORM-2D to demonstrate the drawing process for brass casings. The headstamp punch bunter has a protrusion at the end for the primer pocket and raised lettering all around the face of the punch to form the stamp writing. It is a mirror-image of the case head. Small cases such as the 5.56×45 can be headed in one strike. For larger cases, such as 7.62×51 or 50 BMG, you will need to strike the case once to create the primer pocket. Then, you will need to strike the case a second time to finish the pocket and flatten the head and imprint the writing. This second strike hardens the brass so that it can withstand the pressure of firing. Thanks to Guy Hildebrand of the Cartridge Collectors’ Exchange at OldAmmo.com for providing the 20mm Draw Set photograph. Photo of a Bunter from River Valley Ordnance.