The American Tactical Complete Upper (brand part number ATI15MS450BM) is a drop-in-ready upper receiver assembly chambered in .450 Bushmaster, built around a forged 7075-T6 aluminum Mil-Sport AR-15-pattern upper receiver with a 16-inch, button-cut-rifled barrel in a 1:24 twist and a black nitride finish. It’s completed with a 15-inch free-floated aluminum KeyMod rail system over a low-profile, carbine-length DGIS gas system, an A2-style compensator, and a black nitride-finished bolt carrier group, so everything needed above the receiver is included. As a complete upper with no lower receiver attached, it fits any AR-15-pattern lower and is not itself a regulated firearm — only a complete, serialized lower receiver is regulated under federal law.

Key Specifications

• Chambered in .450 Bushmaster.
• Built on a forged 7075-T6 aluminum Mil-Sport upper receiver.
• Barrel measures 16 inches with a 1:24 twist and black nitride finish.
• Includes a 15-inch free-floated KeyMod rail system.
• Uses a low-profile, carbine-length DGIS gas system.
• Includes an A2-style compensator.
• Includes a black nitride-finished bolt carrier group.
• Fits any AR-15-pattern lower receiver.
• Capacity rated at 5 rounds with compatible magazines.

Frequently Asked Questions

Is this a complete firearm? No, it’s a complete upper assembly with no lower receiver — it fits any AR-15-pattern lower and is not itself a regulated firearm.

Does this upper include the bolt carrier group? Yes, a black nitride-finished BCG is included.

Buy the American Tactical .450 Bushmaster Complete Upper

Add serious big-bore capability to any AR-15 lower. Order this upper from our American Tactical lineup of AR-15 uppers, and our Lubbock, Texas team will get it ready to ship as soon as it’s available.