Daniel Defense DD4 MK18 RIII SBR, 5.56 NATO, 10.3″ Barrel, FDE, California Compliant

Product Description

The Daniel Defense DD4 MK18 RIII in this configuration is a semi-automatic 5.56 NATO NFA short-barrelled rifle with a 10.3" Government profile barrel, 1:7 twist, carbine-length gas system, a RIS III 9.5 M-LOK rail in FDE and a Daniel Defense flash hider, built by Daniel Defense as a California Compliant SKU.

Ten point three inches is the MK18 length, and it exists for close quarters: short enough to be usable inside vehicles, doorways and stairwells, and the length special operations units settled on. What you give up is velocity — 5.56 loses meaningful speed below about 14 inches, which pushes you toward ammunition built for short barrels. What you gain is a rifle you can manoeuvre, and a good suppressor host.

The RIII generation brings ambidextrous controls and an M-LOK rail to the MK18 pattern. The RIS III is modelled on the RIS II two-piece rail Daniel Defense developed for SOCOM but built around M-LOK for less weight, and at 9.5 inches in FDE it runs out to near the muzzle. The carbine gas system is the only practical choice at 10.3 inches, and it runs at higher port pressure — which is why short guns cycle hard and benefit from an adjustable setup when suppressed.

NFA short-barrelled rifle — how this one is bought

This firearm is a short-barrelled rifle regulated under the National Firearms Act. Taking possession requires a BATFE tax stamp and an approved NFA transfer through a dealer holding a Special Occupational Tax stamp. Western Sport is an SOT dealer and handles these transfers as routine business. We give no legal advice or timelines here: call 817-393-4000 and we will explain how a transfer through us works and what we need from you. Browse our NFA firearms.

Key Facts

• Brand / Model: Daniel Defense DD4 MK18 RIII
• Manufacturer Part Number: 02-088-00319-055 | UPC: 818773020435
• Legal category: NFA short-barrelled rifle (SBR) | Class: California Compliant
• Action: Semi-automatic | Caliber: 5.56mm NATO
• Barrel: 10.3", Government profile, 1:7 twist
• Gas system: Carbine length
• Muzzle device: Daniel Defense flash hider
• Rail: Daniel Defense RIS III 9.5, M-LOK attachment, FDE
• Generation features: RIII ambidextrous lower controls and GRIP-N-RIP charging handle
• Brand standard, barrel: Cold hammer forged Chrome Moly Vanadium steel, chrome lined, Mil-Spec heavy phosphate coated, HP/MPI tested
• Brand standard, receivers: CNC machined 7075-T6 aluminium, Type III anodized
• Brand standard, BCG: M16 profile, Mil-Spec MP tested, chrome lined, staked gas key
• Weight, overall length, muzzle thread: call 817-393-4000 to confirm

California Compliant configuration

Daniel Defense builds this SKU as a California Compliant MK18 RIII. That is a separate question from its NFA status, and both have to be satisfied. Compliance requirements change and vary by locality, and state law also governs whether a short-barrelled rifle may be possessed at all. Western Sport makes no claim about legality at your address — verify the rules for your own jurisdiction, then call 817-393-4000. Cross-shop the MK18 configurations and the wider Daniel Defense range.

Ordering from Western Sport in Roanoke, TX

Western Sport is a licensed FFL and an SOT dealer in Roanoke, Texas, a Daniel Defense master dealer since 2007 with a gunsmith on site. This short-barrelled rifle must be transferred through a licensed FFL holding an SOT, and it requires an approved NFA transfer with a tax stamp. Call 817-393-4000 and we will walk you through it start to finish.

Frequently Asked Questions

Q: Does this MK18 RIII require a tax stamp?

A: Yes. It is a short-barrelled rifle under the National Firearms Act, so possession requires a BATFE tax stamp and an approved NFA transfer through a dealer holding a Special Occupational Tax stamp. Western Sport is an SOT dealer; call 817-393-4000 and we will explain how our transfers work.

Q: Why is 10.3 inches the classic MK18 barrel length?

A: Because it is short enough to work in vehicles, doorways and stairwells while still running reliably on a carbine gas system. Special operations units settled on this length for close-quarters work, and Daniel Defense builds its MK18 pattern around a 10.3-inch Government profile barrel.

Q: What does a 10.3-inch barrel cost me in performance?

A: Velocity. 5.56 loses meaningful speed below roughly 14 inches, which affects terminal performance and makes ammunition selection matter more. Loads designed for short barrels work better here than general-purpose ammunition. In exchange you get a far more manoeuvrable rifle and a good suppressor host.

Q: What is the RIS III 9.5 rail on this SBR?

A: A Daniel Defense M-LOK rail modelled on the RIS II two-piece rail developed for SOCOM, rebuilt in M-LOK for lower weight while keeping the durability of the original. At 9.5 inches in FDE it covers this short barrel nearly to the muzzle, leaving an uninterrupted top rail for optics.

Q: Can this short-barrelled rifle be transferred to any state?

A: No, and we will not guess about yours. Some states prohibit short-barrelled rifles outright, and this SKU is also built as a California Compliant configuration, a separate requirement. Verify both for your own jurisdiction, then call 817-393-4000 and we will tell you what we can do.

Q: Is the carbine gas system a compromise at this length?

A: It is the only practical option — there is no room for a longer gas system behind a 10.3-inch barrel. Port pressure is high, so the action cycles hard, which is normal at this length. It is also why many owners of short 5.56 guns run an adjustable setup once a suppressor is added.

Additional information