The CMMG DISSENT Mk4 SBR 5.56mm is a factory short-barreled rifle that gives full AR-15 capability without the bulk of a buffer tube (brand part no. 55A240F-AB). CMMG’s patent-pending direct impingement Compact Action houses the entire action and recoil system in the upper receiver, and a side-folding stock with adjustable length of pull and cheek riser sits at the rear. The 10.5-inch 4140CM barrel has a 1:7 twist and a ZEROED linear compensator on a 1/2×28 thread, and an adjustable .750-inch gas block lets you tune it for suppressed or unsuppressed fire. A forward non-reciprocating charging handle and a 9.6-inch M-LOK handguard with a top Picatinny rail make it quick to run and easy to set up. Two 30-round CMMG magazines ship with it.

Key Specifications

• Chambering is 5.56x45mm on CMMG’s Compact Action direct impingement system.
• Barrel length is 10.5 inches in 4140CM salt-bath nitride, rifled at a 1:7 twist.
• The muzzle device is a CMMG ZEROED linear compensator on a 1/2×28 thread.
• The gas block is an adjustable .750-inch unit for dialing in suppressed or unsuppressed use.
• The handguard is a CMMG 9.6-inch M-LOK design with a top Picatinny rail.
• Magazines included are two CMMG 30-round magazines.
• Weight is 6.8 pounds, with a length of 20.4 to 30.3 inches.

Frequently Asked Questions

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

Can the gas system be tuned for a suppressor? Yes. The adjustable .750-inch gas block lets you dial the gas system in for suppressed or unsuppressed ammunition.

How does the stock fold without a buffer tube? The Compact Action keeps the whole recoil system in the upper receiver, so there is no buffer tube and the stock can fold to the side.

Buy the CMMG DISSENT Mk4 SBR 5.56mm, 10.5-Inch, Armor Black

As of October 9, 2026, this short-barreled rifle transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through CMMG‘s semi-auto rifles lineup and our Lubbock, Texas team will handle the transfer.