The LUTH AR 20" Bull Barrel Rifle Kit with Adjustable Stock is a complete AR-15 build solution for shooters who want to assemble their own rifle without starting from scratch. This kit includes everything except the stripped lower receiver—a fully assembled upper receiver, matched lower parts kit, and your choice of stock configuration. Whether you're building a precision .223/5.56 rifle for the range, target work, or hunting, this kit delivers quality components and modern ergonomics in one package.
The heart of this build is the 20-inch fluted bull barrel chambered in .223 Rem, machined from 416 stainless steel and threaded 1/2 x 28 for suppressor or muzzle device compatibility. The fluted profile reduces weight while maintaining the inherent accuracy of a heavier barrel profile. A 1-9 right-hand twist handles a wide range of .223 ammunition, and the M4 feed ramp ensures reliable feeding. The assembled upper features a rifle-length gas tube matched to the 20-inch barrel and a .936 diameter gas block for tuned performance. You get an A3 upper receiver, fully assembled bolt carrier, and A2 flash hider out of the box.
The 15-inch KeyMod palm handguard provides modern mounting flexibility for lights, lasers, and other tactical accessories. Choose between the MBA-1 fixed rifle buttstock for a classic setup or the MBA-3 adjustable carbine buttstock for quick length-of-pull adjustment. The complete lower parts kit handles the mechanical side—all you need to do is source a mil-spec stripped lower receiver, assemble the lower, and connect the two halves. This is genuine DIY rifle building without the guesswork.
Key Features
- 20-inch fluted bull barrel in .223 Rem, 416 stainless steel for accuracy and corrosion resistance
- Threaded barrel (1/2 x 28) ready for suppressors or muzzle devices
- 1-9 RH twist accommodates standard and heavier .223 loads
- Fully assembled upper receiver with A3 configuration
- 15-inch KeyMod handguard for modern accessory mounting
- Choice of fixed (MBA-1) or adjustable (MBA-3) buttstock
- Complete lower parts kit included; stripped lower receiver not included
- Rifle-length gas system tuned for the 20-inch barrel
Specifications
| Barrel Length | 20 inches |
| Barrel Profile | Fluted bull barrel |
| Chambering | .223 Rem / 5.56 NATO |
| Barrel Material | 416 stainless steel |
| Barrel Twist | 1-9 right-hand |
| Bore Rifling | 6 lands and grooves, button broached |
| Barrel Thread | 1/2 x 28 |
| Gas System | Rifle length |
| Gas Block Diameter | .936 inch |
| Upper Receiver | A3 assembled |
| Bolt Carrier | .223 fully assembled |
| Flash Hider | A2 style |
| Handguard | 15-inch KeyMod palm handguard, vented |
| Lower Parts Kit | Complete LLRPK-1 .223/5.56 kit included |
| Stock Options | MBA-1 fixed or MBA-3 adjustable carbine |
| Lower Receiver | Not included; mil-spec stripped lower required |
Frequently Asked Questions
What do I need to complete this kit?
You'll need to source a mil-spec stripped lower receiver separately. Once you have one, assemble the included lower parts kit into the lower, then attach it to the assembled upper. That's the build—no additional parts required to function.
Is this kit compatible with standard AR-15 uppers and lowers?
Yes. The upper and lower parts are standard mil-spec .223/5.56 components, so they'll work with any mil-spec stripped lower receiver and are compatible with standard AR-15 configuration and accessories.
Can I use a suppressor with this barrel?
Yes. The barrel is threaded 1/2 x 28, which is the standard thread pitch for .223/5.56 suppressors and muzzle devices. The A2 flash hider can be removed and replaced with a suppressor or other threaded accessory.
What's the difference between the MBA-1 and MBA-3 stock options?
The MBA-1 is a fixed rifle buttstock, while the MBA-3 is an adjustable carbine-style buttstock. Choose the fixed stock for a classic, solid setup, or the adjustable stock if you want the ability to change length of pull for different shooting positions or body armor.
