Daniel Defense DD4 MK18 RIII SBR, 5.56 NATO, 10.3″ Barrel, FDE, California Compliant
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Home » Shop » Daniel Defense DD4 MK18 RIII SBR, 5.56 NATO, 10.3″ Barrel, FDE, California Compliant
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$2,682.00Original price was: $2,682.00.$2,494.00Current price is: $2,494.00.
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FREE SUPPRESSOR WITH THIS GUNBuy this firearm and get a free Outlier Backdraft Hunter 4″ suppressor, a $189 value. In stock now, while supplies last. How it works →
Daniel Defense DD4 MK18 RIII short-barrelled rifle in California Compliant configuration: 5.56 NATO, 10.3″ Government profile barrel, carbine gas, RIS III 9.5 M-LOK rail in FDE. NFA item requiring a tax stamp.
Update, October 9, 2026: ATF no longer requires a Form 4, tax stamp, fingerprints or registration for suppressors, short-barreled rifles, short-barreled shotguns or AOWs. They now transfer on a standard Form 4473 with a background check. Anything below that mentions a Form 4, a wait or a tax stamp was written before this change. What changed
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. 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
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. Cross-shop the MK18 configurations and the wider Daniel Defense range.
Ordering from Western Sport
Order online and we ship it to the licensed FFL dealer you choose near you — see how buying a gun online works. Western Sport has been a licensed FFL/SOT dealer since 2007, and everything we sell carries the full manufacturer warranty. Questions before you order? Send us a message.
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; send us a message 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.
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.
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