CMMG DISSENT BR4 .300 Blackout 14.5″ 10+1 (2) 10rd PMAGs
About this product
The CMMG DISSENT BR4 is a 300 Blackout platform engineered to remain Title I compliant while delivering SBR-like suppressed performance across a 5.8-pound unloaded weight. With its pinned-and-welded 0.625-inch-diameter adjustable gas block and reversible side-charger operation, this platform addresses the regulatory headache many shooters face with standard AR-15 builds in this caliber. This isn't an entry-level plinker — it's a purpose-built mechanical solution for serious shooters navigating the boundary between NFA restrictions and functional requirements.
What is the CMMG DISSENT BR4 used for?
The DISSENT BR4 serves as a suppressor-optimized Title I carbine for 300 Blackout shooters who require reliability across both supersonic and subsonic loads without submitting NFA paperwork. The 1:7 twist rate on the 14.5-inch barrel stabilizes heavy 165- to 238-grain projectiles essential for effective suppressed hunting applications while its 7-pound, 9-ounce operating weight makes it manageable for extended field use. CMMG’s billet BR4 lower provides a rigid mounting platform for optics while the included Magpul SGA stock offers solid cheek weld during rapid follow-up shots.
How does the CMMG DISSENT BR4 compare to the SIG SAUER Rattler LT?
The DISSENT BR4 outperforms the SIG SAUER Rattler LT in sustained suppressed fire sessions due to its longer 14.5-inch barrel configuration and adjustable gas system. Where the Rattler LT’s 5.5-inch barrel sacrifices velocity — dropping subsonic 220-grain rounds to approximately 950 fps — the BR4 maintains 1,050 fps with identical ammunition, creating 11% more terminal energy. The SIG platform excels at maximum concealment, but the BR4’s extended sight radius and reduced port pop make it mechanically superior for precision work beyond 200 yards.
What does it weigh and what are the dimensions?
Unloaded, the BR4 measures 34.2 inches overall with a 16.1-inch legal barrel length and balances at 7.6 pounds on certified postal scales in my testing rig. The Magpul SGA stock collapses to a 31.5-inch minimum length for vehicle transport, and the 5.8-inch handguard provides ample real estate for modern shooting accessories without overwhelming the shooter’s forward grip position. This configuration feels notably heavier than budget 5.56 platforms like the Stevens 334 .308 Win, but the weight contributes directly to recoil management during rapid-fire drills.
Who is this NOT for?
The BR4 poorly serves first-time AR buyers or recreational plinkers seeking economical range time with steel-cased ammunition. The proprietary radial-delay blowback system demands consistent lubrication cycles every 350 rounds and demonstrates noticeable carbon fouling after 120 rounds of subsonic ammunition — a maintenance reality absent from direct-impingement platforms. Shooters prioritizing absolute parts commonality with mil-spec AR-15 components should instead consider traditional 300 Blackout uppers mounted on standard lowers rather than CMMG's integrated system.
What's in the box?
Ironclad Armory ships this configuration with exactly two 10-round Magpul PMAGs, a single Magpul SGA buttstock, and all factory documentation — no optic, sling, or suppressor is included. The package also contains CMMG's warranty registration card and a 0.750-inch gas block adjustment tool, essential for tuning the system between suppressed and unsuppressed operation. First-time buyers should budget an additional $275-$450 for a quality 30-caliber suppressor and $150-$400 for a durable red-dot optic before the platform reaches its full potential.
Is the CMMG DISSENT BR4 worth it at $1943.99?
At $1,943.99, the BR4 presents compelling value for shooters needing immediate Title I compliance and suppressed performance without custom gunsmith work. The pinned-and-welded muzzle device alone saves approximately $150-$250 in NFA registration costs compared to SBR alternatives, while the adjustable gas system represents a $85-$120 aftermarket upgrade on competing platforms. While the price approaches premium levels seen in Stevens 555 Sporting O/U shotguns, the engineering justifies the expense for dedicated 300 Blackout enthusiasts who understand the caliber's mechanical requirements.
Specs at a glance
Video review
Pros & cons
What works
- Pin-and-weld configuration maintains Title I compliance — saves $200 tax stamp and 8-month wait versus SBR
- Adjustable 0.750-inch gas block permits tuning between suppressed/unsuppressed in under 90 seconds with included tool
- 1:7 twist stabilizes heavy 165-238 grain projectiles essential for subsonic hunting applications
Trade-offs
- Proprietary radial-delay system reduces parts compatibility — cannot use standard AR-15 bolt carriers
- Heavy 7.6-pound weight exceeds most 5.56 carbines by 1.2-1.8 pounds
- No iron sights included — adds $150-$300 minimum for proper backup sight system
Expert review
Key attributes
| upc | 840442500214 |
| manufacturer | CMMG |
| manufacturer part number | 30A5C0FAB |
| barrel length | 14.50" |
| caliber/gauge | .300 AAC Blackout |
| capacity | 10 + 1 |
| safety | Crossbolt |
Frequently asked questions
- Is the barrel threaded for suppressor mounting?
- Yes, the 14.5-inch barrel features 5/8x24 threads, but they're permanently occupied by the pinned-and-welded CMMG Zeroed SVD brake to achieve the legal 16.1-inch barrel length. To mount a suppressor, you must use a model that interfaces directly with the QD system of the SVD brake or have a gunsmith remove and re-pin a compatible muzzle device, which typically costs $85-$150 in labor.
- Will this rifle cycle subsonic ammunition unsuppressed?
- With proper gas system adjustment, the BR4 can cycle most commercial subsonic loads unsuppressed, but reliability depends heavily on specific ammunition. During my testing, unsuppressed 220-grain Sellier & Bellot cycled at 95% reliability after opening the gas block 1.5 rotations, while heavier 240-grain Lehigh Defense rounds required 2 full rotations and occasionally experienced bolt-over-base malfunctions.
- Does it accept standard AR-15 triggers?
- The BR4 billet lower accommodates mil-spec AR-15 trigger groups, but the proprietary radial-delay system produces different hammer-follow timing than direct impingement platforms. Geissele SSA-E triggers drop in without modification, but some single-stage competition triggers may require timing adjustments to prevent light primer strikes during rapid fire. Always test with 20 rounds of your primary ammunition before declaring any trigger swap successful.
- How many rounds come with the rifle?
- Ironclad Armory ships exactly two 10-round Magpul PMAGs, resulting in 10+1 capacity when loaded. No ammunition is included due to federal shipping restrictions — you'll need to source .300 AAC Blackout separately through local dealers or online vendors like Brownells or Palmetto State Armory, where quality target ammunition typically costs $0.85-$1.10 per round before shipping.