The 12.7x42mm is a powerful big bore cartridge designed for use in AR style rifles. The brass case is essentially a lengthened 50 AE (1.650 long) with a rebated 7.62x39 style head. This brass case is designed to use a large magnum pistol primer. Starline is a family owned business and prides itself on producing the highest quality brass case available. With a production process focused on quality not quantity, Starline makes the finest brass and has for more than 40 years out of their state-of-the-art manufacturing facility in Sedalia, MO. Mfg: Starline