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Daniel Defense AR-15 Pistol MK18 Upper Receiver Assembly 5.56x45mm 10.3"
Our editorial team reviews specifications, product data, and field-use information to keep pages accurate.
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SKU: 23-004-08013-011-852548002592
Overview
Built for shooters who want a compact upper patterned after the Mk18 Mod 1, this assembly is suited to pistol builds or registered SBR setups where a short, maneuverable platform is the priority. It combines a 10.3-inch chrome-lined barrel, a true 5.56x45 NATO chamber, and M4 feed ramps, along with a bolt carrier assembly that has undergone MPI testing. The free-float RIS II Mk18 quad-rail provides space for accessories while leaving a continuous top rail for optic or iron sight setups. Complete with a charging handle assembly and flash hider, it offers a ready-to-install upper for a serious AR-15 build.
Why Hunters Choose the Daniel Defense
Faithful Recreation
Of the US Navy Mk18
10.3-inch Cold
Hammer forged barrel with chrome-lined
True 5.56x45
NATO chamber supports commercial and
M4 Feed
Ramps and MPI-tested bolt carrier
Ris Ii
Mk18 free-float quad rail offers
Key Features
- 10.3-inch complete AR-15 pistol upper assembly in 5.56x45mm NATO.
- Faithful recreation of the US Navy Mk18 Mod 1 platform.
- Cold hammer forged 4150 chrome-moly vanadium steel barrel with chrome lining.
- M4 feed ramps and true 5.56x45 NATO chamber for broad ammunition compatibility.
- RIS II Mk18 9.5-inch free-float quad-rail handguard in Flat Dark Earth.
- Includes charging handle assembly and Daniel Defense flash hider.
Best Used For
- Shooters building a Mk18-style AR-15 pistol or registered SBR setup.
- Users wanting a complete upper with rail space for optics and accessories.
- Hunters and shooters who prefer a compact 10.3-inch 5.56x45mm NATO upper.
- Those seeking a drop-on upper for compatible AR-15 pistol lower receivers.
Specifications
| Barrel Contour | Government |
|---|---|
| Barrel Finish | Mil-Spec Heavy Phosphate |
| Barrel Length | 10.3 Inches |
| Barrel Material | 4150 Chrome Moly Vanadium Steel |
| Blade Finish | Flat Dark Earth |
| Bolt Carrier Assembly Included | Yes |
| Cartridge | 5.56x45mm NATO |
| Chamber | 5.56x45 NATO |
| Charging Handle Included | Yes |
| Chrome Lined | Yes |
| Compatible With | AR-15 |
| Free Floats Barrel | Yes |
| Gas Block | Pinned, Low Profile |
| Gas Block Diameter | 0.75 Inches |
| Gas Key Staked | Yes |
| Gas System Length | Carbine |
| Handguard | RIS II Mk18 Quad Rail, Free Float |
| Handguard Length | 9.5 Inches |
| M4 Feed Ramps | Yes |
| Magnetic Particle Inspection Mpi | Yes |
| Material | Aluminum |
| Mil Spec Or Commercial | Mil-Spec |
| Muzzle Device | Daniel Defense Flash Hider |
| Optic Ready | Yes |
| Rail Type | Quad-Rail |
| Sights | No |
| Threads | 1/2"-28 |
| Twist | 1:7 Inches |
| Upper Receiver | A4 Flat-Top |
| Upper Receiver Type | A3 Flat-Top |
Pros
- Faithful recreation of the US Navy Mk18 Mod 1 platform.
- 10.3-inch cold hammer forged barrel with chrome-lined bore.
- True 5.56x45 NATO chamber supports commercial and surplus mil-spec ammunition.
- M4 feed ramps and MPI-tested bolt carrier assembly support reliable operation.
- RIS II Mk18 free-float quad rail offers space for accessories and optics.
- Includes charging handle assembly and Daniel Defense flash hider for a complete upper.
Considerations & Trade-offs
- The 10.3" barrel and carbine gas system make this a compact upper, which can be a trade-off if you want more dwell time or a longer sight radius.
- It is sold as an upper receiver assembly only, so it still requires a compatible pistol or registered SBR lower receiver to complete the build.
- The A3 flat-top receiver is optic- and sight-ready, but no sights are included.
- The RIS II Mk18 quad-rail offers substantial accessory mounting space, though the added rail surface can be bulkier than simpler handguard setups.
Suggested Comparisons
- AR-15 pistol upper receiver assemblies
- Complete upper receiver assemblies
- 5.56x45mm NATO upper assemblies
- Free-float quad-rail handguard uppers
Suggested Accessories
- AR-15 upper receiver optic mount
- Backup iron sights
- Weapon light
- Rail-mounted foregrip
Frequently Asked Questions
What platform is this upper receiver assembly based on?
It is described as a faithful recreation of the US Navy's Mk18 Mod 1 platform.
What caliber and chambering does it use?
It is chambered in 5.56x45mm NATO, and the description says it may safely use both commercial and higher-pressure surplus mil-spec ammunition.
Does this upper include a handguard and muzzle device?
Yes. It comes with a 9.5" Flat Dark Earth RIS II Mk18 Quad-Rail Handguard and a Daniel Defense Flash Hider.
Is this upper ready for optics or iron sights?
The A4 Flat-Top receiver is described as able to accommodate a shooter's chosen optic and/or iron sight arrangement. Sights are not included.
What lower receivers is it compatible with?
The product data says it is ready to drop onto any pistol or registered SBR small pin lower receiver, and it is listed as compatible with AR-15.