SAAMI-standardized big-bore AR-15 cartridge. Legal for deer hunting in many straight-wall-only states. Most commercially successful large-bore AR cartridge.
Type: Rifle
Introduced: 2007, United States
Parent case: .284 Winchester
Standardization: SAAMI
Bullet diameter: 0.452" (11.48 mm)
Case length: 1.7" (43.18 mm)
Overall length: 2.26" (57.4 mm)
Max pressure: 38,500 PSI
Rim type: Rebated
Primer: Large Rifle
Typical twist rate: 1:24
Muzzle velocity: 2100–2300 fps
Muzzle energy: 2400–2900 ft-lbs
Effective range: 250 yd
Common bullet weights: 245, 250, 260, 300 gr
Primary use: Hunting
Production status: Active
Also known as: .450 BM · 11.5x43mm
History: Originally developed by Tim LeGendre and licensed to Bushmaster in 2007. Commercialized with Hornady ammunition support. SAAMI standardization gave it advantage over proprietary competitors. Became very popular when several Midwestern states legalized straight-wall cartridges for deer hunting. Ohio, Indiana, and Michigan hunters embraced it. Most commercially successful of the AR-15 big-bore…
Notable firearms: Ruger AR-556, Bushmaster AR-15, CVA Scout rifle, Various AR-15 uppers
Similar cartridges: .458 SOCOM, .50 Beowulf, .45-70 Government