Big-bore AR-15 cartridge for hunting and close-range power. Designed to chamber in standard AR-15 with minimal modifications. Devastating stopping power.
Type: Rifle
Introduced: 2001, United States
Parent case: None
Standardization: Proprietary
Bullet diameter: 0.5" (12.7 mm)
Case length: 1.65" (41.91 mm)
Overall length: 2.25" (57.15 mm)
Max pressure: 33,000 PSI
Rim type: Rebated
Primer: Large Pistol
Typical twist rate: 1:20
Muzzle velocity: 1700–2000 fps
Muzzle energy: 2200–2900 ft-lbs
Effective range: 200 yd
Common bullet weights: 300, 325, 350, 400 gr
Primary use: Hunting, Self Defense
Production status: Active
Also known as: 12.7x42mm
History: Developed by Bill Alexander in 2001 specifically for AR-15 platform. Named after the legendary warrior Beowulf. Designed to provide big-game hunting power and barrier-penetration capability in AR-15. Uses standard AR-15 bolt face and magazines (though reduced capacity). Popular for hog hunting, home defense, and close-range hunting. Competes with .458 SOCOM and .450 Bushmaster in AR-15 big-bore…
Notable firearms: Alexander Arms AR-15 rifles, Various AR-15 uppers, Custom AR builds
Similar cartridges: .458 SOCOM, .450 Bushmaster, .499 LWR