The LUTH AR 20" Bull Barrel Rifle Kit with Fixed Stock is a complete AR-15 build solution for shooters who want precision and control without buying components piecemeal. This kit delivers everything except the stripped lower receiver—upper assembly, complete lower parts kit, and your choice of stock. It's built for hunters and precision rifle enthusiasts who value accuracy over modularity, with a fluted bull barrel engineered for consistent shot placement and minimal thermal drift.
The 20-inch fluted bull barrel is where this kit earns its reputation. Chambered in .223 Rem and forged from 416 stainless steel, it's threaded 1/2 x 28 for suppressor or muzzle device compatibility. The button-broached barrel offers 1-in-9 right-hand twist and M4 feed ramps, suited to a wide range of .223 loads. A .936 gas block and rifle-length gas tube keep the action running clean across standard pressure ammunition, while the A2 flash hider manages muzzle signature. The 15-inch KeyMod handguard gives you rail real estate for lights, lasers, or grips without unnecessary bulk.
Assembly is straightforward: drop the included complete lower parts kit into your own stripped lower, attach the upper, choose your stock, and you're ready to shoot. Luth-Ar's design philosophy favors simplicity and repeatability—no guessing, no missing parts. The fluted profile manages recoil impulse and heat naturally, making this kit a solid choice for target work, hunting, or learning AR ergonomics without the sticker shock of buying everything separately.
Key Features
- 20-inch fluted bull barrel in 416 stainless steel for accuracy and heat management
- Complete upper assembly—no additional components needed above the lower
- Complete lower parts kit included; assemble into any mil-spec stripped lower
- Choice of fixed stock (MBA-1) or adjustable carbine stock (MBA-3)
- 15-inch KeyMod handguard for accessory mounting
- 1/2 x 28 threaded barrel for suppressors and muzzle devices
- Rifle-length gas system with A2 flash hider
- M4 feed ramps and button-broached bore for reliable feeding
Specifications
| Caliber | .223 Rem |
| Barrel Length | 20 inches |
| Barrel Profile | Fluted bull barrel |
| Barrel Material | 416 stainless steel |
| Twist Rate | 1 in 9, right-hand |
| Thread Pitch | 1/2 x 28 |
| Rifling | 6 lands and grooves, button-broached |
| Feed Ramps | M4 |
| Gas System | Rifle-length gas tube |
| Gas Block Diameter | .936 inch |
| Muzzle Device | A2 flash hider |
| Handguard | 15-inch KeyMod palm handguard, vented |
| Upper Receiver | Assembled A3 upper |
| Bolt Carrier | Fully assembled .223 bolt carrier group |
| Stock Options | MBA-1 fixed rifle stock or MBA-3 adjustable carbine stock |
| Lower Parts Kit | Complete LLRPK-1 kit for .223/5.56 |
Frequently Asked Questions
What do I need to complete this kit?
You'll need a mil-spec stripped lower receiver, which is sold separately. Once you have the lower, assemble the included lower parts kit into it, attach the upper assembly, choose your stock, and you're done. No other components are required to fire.
Can I use this kit with a suppressor?
Yes. The 20-inch barrel is threaded 1/2 x 28, the standard pitch for .223 suppressors and muzzle devices. The A2 flash hider can be removed and replaced with any compatible suppressor or muzzle brake.
Does this kit come with a lower receiver?
No. The kit does not include a stripped lower receiver. You must purchase one separately and transfer it through an FFL if required by your local laws. Luth-Ar recommends a mil-spec stripped lower for compatibility.
What's the difference between the two stock options?
The MBA-1 is a fixed rifle stock, while the MBA-3 is an adjustable carbine stock. Choose based on your preference for cheek weld length and modularity. The kit ships with one or the other depending on your selection.
