Daniel Defense DDM4 300S SBR, .300 Blackout

Product Description

The Daniel Defense DDM4 300S is a semi-automatic NFA short-barrelled rifle chambered in .300 Blackout, built on a 10.3" S2W heavy profile cold hammer forged barrel with a 1:8 twist, a pistol-length gas system, a DDM4 Rail 9.0 Picatinny quad rail and a Daniel Defense flash suppressor.

This is the rifle .300 Blackout was designed for. The cartridge exists to put a .30-calibre bullet through an AR-15 sized action using standard 5.56 bolts and magazines, and to do it from a short barrel: unlike 5.56, Blackout burns its powder in about ten inches, so a 10.3" barrel is the intended configuration, not a compromise. The result is greater muzzle energy than a comparable 5.56 platform of the same barrel length.

It is also the best suppressor host in the AR-15 family. Subsonic .300 Blackout loads, fired from a short barrel behind a can, are about as quiet as a centrefire rifle gets, and the pistol-length gas system is sized to cycle them. Supersonic loads out of the same rifle give you hunting and defensive performance. Muzzle thread is 5/8 x 24 TPI, the .30-calibre standard, so suppressor and muzzle device selection is straightforward. The rifle weighs 5.77 lbs with an overall length of 26 3/4 to 29 7/8 inches.

NFA short-barrelled rifle — how it transfers

This firearm is a short-barrelled rifle regulated under the National Firearms Act. 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, so the transfer can be completed here. We give no legal advice or timelines on this page — call 817-393-4000 and we will explain the steps as they run through our shop. See our NFA firearms and suppressors categories.

Key Facts

• Brand / Model: Daniel Defense DDM4 300S
• Manufacturer Part Number: 02-122-17026-047 | UPC: 815604018210
• Legal category: NFA short-barrelled rifle (SBR)
• Action: Semi-automatic | Caliber: 300 BLK (.300 Blackout)
• Barrel: 10.3", S2W heavy profile, 1:8 twist, cold hammer forged
• Barrel material / finish: Chrome Moly Vanadium steel; chrome lined, heavy phosphate finished, HP/MPI tested
• Gas system: Pistol length
• Muzzle device: Daniel Defense flash suppressor, 17-4 PH stainless steel, salt bath nitride
• Muzzle thread: 5/8 x 24 TPI
• Rail: Daniel Defense DDM4 Rail 9.0, CNC machined 6061-T6 aluminium, Type III hard coat anodized
• Receivers: CNC machined 7075-T6 aluminium, Type III anodized; Mil-Spec lower, flared magazine well, rear QD point
• Bolt carrier group: M16 profile, Mil-Spec MP tested, chrome lined, properly staked gas key
• Furniture: Daniel Defense buttstock, pistol grip and vertical grip
• Magazine: Magpul PMAG 30 AR 300 B GEN M3; uses standard 5.56 bolts and magazines
• Weight: 5.77 lbs | Overall length: 26 3/4" – 29 7/8" with muzzle device
• Origin: Made in the USA

Why .300 Blackout and not 5.56 at this length

Because 5.56 needs barrel length to work and .300 Blackout does not. Cut a 5.56 barrel to 10.3 inches and you lose velocity the cartridge depends on; Blackout was designed around that length and delivers a heavier .30-calibre projectile with greater muzzle energy. Add quiet subsonic loads through a suppressor and the case is hard to argue with. Browse ammunition.

Ordering from Western Sport in Roanoke, TX

Western Sport is a licensed FFL and SOT dealer in Roanoke, Texas, a Daniel Defense master dealer since 2007, with a gunsmith on site. This short-barrelled rifle requires an approved NFA transfer and tax stamp through an SOT dealer. Call 817-393-4000 and we will take it from the beginning.

Frequently Asked Questions

Q: Does the DDM4 300S require a tax stamp?

A: Yes. It is a factory short-barrelled rifle regulated 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 a transfer through us works.

Q: Why is .300 Blackout better than 5.56 in a 10.3-inch barrel?

A: Because it was designed for that length. .300 Blackout burns its powder in roughly ten inches, so a short barrel is the intended configuration rather than a compromise, and it delivers a heavier .30-calibre projectile with greater muzzle energy than a comparable 5.56 platform of the same barrel length.

Q: Can I use my existing AR-15 magazines and bolt?

A: Yes. The 300S uses standard 5.56 bolts and magazines, one of the cartridge’s main design advantages. Daniel Defense specifies the Magpul PMAG 30 AR 300 B GEN M3 for this rifle; a magazine marked for Blackout helps prevent mixing it up with 5.56 ammunition.

Q: What muzzle thread does the 300S have for a suppressor?

A: 5/8 x 24 TPI, the standard .30-calibre thread, fitted at the factory with a Daniel Defense flash suppressor in 17-4 PH stainless steel. That makes suppressor and muzzle device selection straightforward. The suppressor is a separate NFA purchase with its own transfer and stamp.

Q: Why a pistol-length gas system?

A: Because a 10.3-inch barrel has no room for anything longer, and because .300 Blackout — especially subsonic loads behind a suppressor — needs the port early to cycle reliably. It is the correct pairing for this cartridge and length, not a limitation.

Q: How heavy is the 300S?

A: 5.77 lbs, with an overall length of 26 3/4 to 29 7/8 inches including the muzzle device as the stock is adjusted. That is light for a .30-calibre rifle, and the practical appeal of the platform: real .30-calibre performance in a package smaller than most 5.56 carbines.

Additional information