Experience the power of the .450 Bushmaster Ar15 in a compact, left-handed AR platform. The Mid State Firearms Left Handed 10.5″ .450 Bushmaster Upper is built with premium components and assembled by experienced builders who pay careful attention to every detail. From proper barrel installation and gas system alignment to final inspection, each upper is built with reliability and long-term performance in mind.
At the heart of this upper is a 10.5″ 4150 steel barrel featuring an enlarged feed ramp to enhance feeding reliability with the larger .450 Bushmaster cartridge. The barrel is threaded 5/8×32, making it compatible with suppressors and muzzle devices designed for the .450 Bushmaster thread pattern.
The billet left-handed slick side upper receiver features an enlarged ejection port for dependable extraction and ejection while directing spent brass away from left-handed shooters. A carbine-length gas system, .750 low-profile steel gas block, and stainless steel gas tube are properly installed to provide smooth, reliable cycling.
The upper is finished with a lightweight 10″ free-float M-LOK handguard, providing ample space for accessories without adding unnecessary weight. An included A2 flash hider completes the package and helps reduce visible muzzle flash.
Features
- Chambered in .450 Bushmaster
- 10.5″ 4150 steel barrel
- 5/8×32 threaded muzzle (suppressor ready)
- Enlarged feed ramp for improved feeding reliability
- Billet left-handed slick side upper receiver
- Enlarged ejection port
- Left-side ejection
- Carbine-length gas system
- .750 low-profile steel gas block
- Stainless steel gas tube
- 10″ free-float M-LOK handguard
- A2 flash hider included
- Assembled with careful attention to detail using quality components
- Proudly made in the USA
Built the Right Way
A quality upper is more than a collection of parts. Every Mid State Firearms upper is professionally assembled using proven components and careful assembly practices to help ensure proper fit, reliable function, and consistent performance. We take pride in building uppers we’d trust on our own rifles, giving you confidence whether you’re headed into the field, to the range, or adding a unique left-handed big bore AR to your collection.
Note: This upper uses the standard 5/8×32 thread pattern for .450 Bushmaster barrels. Always verify compatibility before installing any muzzle device or suppressor.
Test Fired for Quality (when purchased with BCG)
When this upper is purchased with the optional left-handed bolt carrier group and charging handle, we test fire it prior to shipment with that exact BCG. This additional quality control step helps verify proper function, feeding, extraction, ejection, and gas system operation before it leaves our shop.
If you purchase the upper without a bolt carrier group, it is still professionally assembled and inspected, but cannot be test fired prior to shipping.
Why Buy From Mid State Firearms?
With over 12 years in business, Mid State Firearms has built a reputation for providing quality AR-15 components, Glock parts, and complete firearm solutions to customers across the country. We understand that a firearm component is only as reliable as the attention to detail that goes into building it.
Our uppers are not simply pulled from a shelf and shipped. Each Mid State Firearms upper is professionally assembled, properly torqued, inspected, and built using quality components from trusted manufacturers. We take pride in careful assembly practices and attention to detail because reliability starts before the first round is ever fired.
When you choose a Mid State Firearms upper, you’re buying from an established company with years of experience in the firearms industry—not an anonymous marketplace seller.
When purchased with the optional left-handed bolt carrier group and charging handle, the upper is assembled as a complete system and test fired before shipment to verify proper feeding, extraction, ejection, and cycling.
Our goal is simple: provide well-built firearm components that customers can install with confidence and depend on for years of use.
Why Choose .450 Bushmaster?
The .450 Bushmaster was developed to bring true big-bore performance to the familiar AR-15 platform. Firing .45-caliber bullets with substantial energy, it has become a popular choice for hunters pursuing whitetail deer, hogs, black bear, and other medium to large game.
The cartridge is especially popular in states that require or encourage straight-wall cartridges for deer hunting, offering excellent terminal performance while allowing shooters to continue using the AR-15 platform they already know.
Compared to smaller intermediate cartridges, the .450 Bushmaster delivers tremendous stopping power at practical hunting distances while maintaining straightforward operation with standard AR-15 controls.
Ideal Uses
The compact 10.5″ configuration is well suited for a variety of applications, including:
- Hog hunting from vehicles, blinds, or dense brush
- Compact hunting rifles where maneuverability matters
- Suppressor-ready builds using compatible 5/8×32 muzzle devices
- Ranch and property defense against nuisance animals
- Range shooting for shooters who appreciate the recoil and authority of a true big-bore AR
- Left-handed shooters looking for a purpose-built upper with left-side ejection
Whether you’re building a compact truck gun, a suppressor host, or a hard-hitting hunting rifle, this upper delivers the power of the .450 Bushmaster in a reliable, professionally assembled package.
sound of freedom – This was a great set up. I loved being able to customize the set up. Only issue I had was my own fault as a newb to building these. I used a heavy barrel in a slim hand guard. It makes adding attachments tough with clearances. Hoping someday to also get an AR10 from here.