CMMG Dissent Mk4 .300 Blackout
Model: 30A750A-AB
CMMG Dissent Mk4 .300 Blackout
Model: 30A750A-AB
Full Specifications
About This Firearm
The CMMG Dissent Mk4 is not a standard AR-15. It runs a bufferless, compact action that eliminates the buffer tube entirely, which is what makes the side-folding stock possible. CMMG calls it a "compact action" — it uses a short-stroke piston-adjacent operating rod and a low-mass bolt carrier specifically engineered to cycle at the lower pressures generated by subsonic 220gr .300 BLK loads. That distinction matters: most direct-impingement AR-15s need an adjustable gas block or aftermarket buffer to cycle subsonic ammo reliably. The Dissent does it without either.
CMMG offers the Dissent Mk4 in multiple barrel lengths — the 16.1" rifle variant here is the legal carbine configuration, but the platform also comes in 6" and 8" pistol variants for buyers who want shorter barrels with a brace configuration. The 1:7" twist handles the heavy subsonic bullet weights. A non-reciprocating side charging handle is standard and can be configured left or right. Compared to the Daniel Defense DDM4 at a similar price tier, the Dissent is meaningfully different in its operating system, not just a different brand on the same AR spec sheet.
What the Dissent does better than any other .300 BLK carbine at this tier is subsonic cycling. The low-mass bolt and purpose-built gas system mean subsonic 220gr loads run without the fiddling — no adjustable gas block to tune, no heavy buffer to swap in. Owners and reviewers consistently report it as one of the most reliable subsonic hosts in an AR-pattern rifle. If suppressed subsonic shooting is the primary use case, this is the purpose-built tool for it.
Best For
Strengths & Limitations
- The bufferless compact action and low-mass bolt carrier cycle subsonic 220gr .300 BLK loads reliably without an adjustable gas block or heavy buffer — a problem that plagues most standard AR-15 conversions in this caliber.
- Ships with two Magpul PMAGs, a side-charging handle, and a folding stock. That's a more complete out-of-box configuration than the DDM4 V7 at a comparable price tier.
- The proprietary compact action means standard AR-15 buffer systems, bolt carriers, and some lower parts will not transfer. Owners used to mixing and matching AR parts should verify compatibility before swapping components.
- At 102.4 oz (6.4 lbs), the Dissent is heavier than its folding-stock profile implies. The bufferless action and folding mechanism add weight that buyers focused on a light-carry suppressor host should factor in — the Q Honey Badger at 72 oz is the lighter route in this caliber.
- Cerakote finish in Armor Black looks good but is not as durable as Type III hard anodize on receivers that see regular suppressor-mount torquing. Cerakote can chip at contact points over time.
Compatible Ammunition
Find the best prices on compatible .300 Blackout ammunition.
Shop .300 Blackout Ammo →Ballistics Calculator
Calculate trajectory, drop, and energy for .300 Blackout ammunition.
.300 Blackout Ballistics →Where to Buy
No prices available at this time.
Frequently Asked Questions
Which CMMG Dissent Mk4 variant should I choose?
CMMG offers the Dissent Mk4 in three barrel lengths in .300 Blackout: 16.1" (this rifle variant), 8" (pistol), and 6" (pistol). The 16.1" is the only configuration that ships as a legal rifle without NFA paperwork. The 8" and 6" pistol variants need a stabilizing brace or SBR registration to shoulder. For suppressed subsonic use, community consensus is that .300 BLK gives up little ballistically going from 16" down to 8-9" — but you gain NFA complexity. If you want a registered rifle with no paperwork, the 16.1" is it. If you already own a suppressor and are comfortable with the NFA process, the 8" pistol is worth serious consideration.
Will standard AR-15 magazines and lowers work with the CMMG Dissent?
Standard STANAG AR-15 magazines fit and feed correctly — the Dissent ships with two Magpul PMAGs. However, the lower receiver and action are proprietary CMMG components. A standard AR-15 buffer tube, buffer, and recoil spring are absent by design. If you're planning to swap lowers or build on the Dissent upper with an off-the-shelf lower, it won't work — the compact action requires the CMMG-matched lower. Magazines and most external controls are standard; the internals are not.
