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.
.50 Beowulf®, Beowulf®, .50 Beo® and Beo® are registered trademarks of Alexander Industries Inc., and are in no way affiliated with Starline Brass®
**WARNING** In firearms that use a floating firing pin (such as the AR-15 and its variants), dropping the bolt on a chambered round could lead to a slam fire. It is important that these firearms are loaded from the magazine so that the bolt loses inertia when it strips a round from the magazine. It is also important NOT to use sensitive primers that aren’t designed for use in an AR, as this increases the chance of a slam fire.