Rock River Arms126513816
RRA Complete Carbine A4 Upper 350 Legend 16" Barrel 10-Round Capacity$744.05
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Availability: In Stock
The Rock River Arms complete mid-length A4 upper receiver in .450 Bushmaster is a ready-to-run upper assembly built for shooters who want serious stopping power in an AR platform. Chambered in .450 BM with a 16-inch chrome moly barrel and 1:24 twist rate, this upper arrives as a complete package—bolt carrier group, charging handle, and 5-round magazine included—so you can mount it straight to a compatible lower receiver and get to work. Mid-length gas system tuning keeps recoil manageable and cycling reliable, whether you're hunting medium to large game, running drills at the range, or building a specialized hunting rifle.
The 13-inch free float rail uses M-Lok attachment points, giving you genuine, repeatable accuracy by isolating the barrel from pressure points on the handguard. Rock River Arms paired it with their Operator Brake (5/8-32 thread) to help manage the cartridge's substantial report and muzzle rise. Everything here—the rail, brake, barrel profile, and gas system—is engineered for the recoil signature of .450 Bushmaster, so you get a coherent, function-tested assembly rather than a collection of generic parts.
This is a workhorse upper for hunters, competition shooters, or anyone building a dedicated .450 BM rifle on an AR lower. Rock River Arms has been backing quality AR uppers for two decades, and their reputation for fit and reliability is well-earned in the field.
| Cartridge | .450 Bushmaster |
| Barrel Length | 16 inches |
| Barrel Material | Chrome Moly |
| Twist Rate | 1:24 |
| Gas System | Mid-Length |
| Rail Type | RRA Lightweight Free Float, 13 inches |
| Rail Attachment | M-Lok Compatible |
| Muzzle Device | RRA Operator Brake, 5/8-32 Thread |
| Gas Block | Low Profile |
| Includes | Bolt Carrier Group, Charging Handle Assembly, 5-Round Magazine |
| Upper Style | A4 Mid-Length |
Yes. This is a standard A4 upper receiver and will drop onto any mil-spec AR-15 lower. Just verify your lower is chambered or will accept a .450 Bushmaster—this upper is caliber-specific.
The complete upper assembly includes the bolt carrier group, charging handle assembly, and one 5-round magazine. You'll need to supply the lower receiver and any additional magazines or accessories.
Yes. The 13-inch RRA free float rail isolates the barrel from the handguard, which supports accuracy by eliminating pressure points. It uses M-Lok slots for mounting optics, lights, and other gear.
The RRA Operator Brake helps reduce muzzle rise and recoil impulse, making follow-up shots faster and more controllable—useful for hunting, competition shooting, or extended range sessions with a cartridge as powerful as .450 Bushmaster.
SKU: 126513769 • Width: 5.5in • Height: 5.5in • Depth: 32in • Weight: 6.44oz
Availability: In Stock
The Rock River Arms complete mid-length A4 upper receiver in .450 Bushmaster is a ready-to-run upper assembly built for shooters who want serious stopping power in an AR platform. Chambered in .450 BM with a 16-inch chrome moly barrel and 1:24 twist rate, this upper arrives as a complete package—bolt carrier group, charging handle, and 5-round magazine included—so you can mount it straight to a compatible lower receiver and get to work. Mid-length gas system tuning keeps recoil manageable and cycling reliable, whether you're hunting medium to large game, running drills at the range, or building a specialized hunting rifle.
The 13-inch free float rail uses M-Lok attachment points, giving you genuine, repeatable accuracy by isolating the barrel from pressure points on the handguard. Rock River Arms paired it with their Operator Brake (5/8-32 thread) to help manage the cartridge's substantial report and muzzle rise. Everything here—the rail, brake, barrel profile, and gas system—is engineered for the recoil signature of .450 Bushmaster, so you get a coherent, function-tested assembly rather than a collection of generic parts.
This is a workhorse upper for hunters, competition shooters, or anyone building a dedicated .450 BM rifle on an AR lower. Rock River Arms has been backing quality AR uppers for two decades, and their reputation for fit and reliability is well-earned in the field.
| Cartridge | .450 Bushmaster |
| Barrel Length | 16 inches |
| Barrel Material | Chrome Moly |
| Twist Rate | 1:24 |
| Gas System | Mid-Length |
| Rail Type | RRA Lightweight Free Float, 13 inches |
| Rail Attachment | M-Lok Compatible |
| Muzzle Device | RRA Operator Brake, 5/8-32 Thread |
| Gas Block | Low Profile |
| Includes | Bolt Carrier Group, Charging Handle Assembly, 5-Round Magazine |
| Upper Style | A4 Mid-Length |
Yes. This is a standard A4 upper receiver and will drop onto any mil-spec AR-15 lower. Just verify your lower is chambered or will accept a .450 Bushmaster—this upper is caliber-specific.
The complete upper assembly includes the bolt carrier group, charging handle assembly, and one 5-round magazine. You'll need to supply the lower receiver and any additional magazines or accessories.
Yes. The 13-inch RRA free float rail isolates the barrel from the handguard, which supports accuracy by eliminating pressure points. It uses M-Lok slots for mounting optics, lights, and other gear.
The RRA Operator Brake helps reduce muzzle rise and recoil impulse, making follow-up shots faster and more controllable—useful for hunting, competition shooting, or extended range sessions with a cartridge as powerful as .450 Bushmaster.
SKU: 126513769 • Width: 5.5in • Height: 5.5in • Depth: 32in • Weight: 6.44oz