CMMG 5.7x28mm 5" Barrel & BCG Kit – Radial Delayed Blowback

5.7x28mm

CMMG 5.7x28mm 5" Barrel & BCG Kit | Radial Delayed Blowback

The CMMG 5.7x28mm 5" Barrel and BCG Kit provides a compact barrel-and-bolt system for compatible AR-platform firearms chambered in 5.7x28mm. Featuring CMMG's patented Radial Delayed Blowback (RDB) operating system, this matched kit combines an ultra-compact 5" 416 stainless steel barrel with the corresponding CMMG bolt carrier group.

CMMG's Radial Delayed Blowback design differs from traditional straight-blowback operation by using bolt rotation to delay the action. This allows CMMG to reduce the reciprocating mass required by conventional blowback designs while providing a smoother operating system.

With its 5" barrel, 1:9 twist, 1/2x28 muzzle threads, and salt-bath nitride finish, this kit is particularly suited to compact 5.7x28 AR configurations.

5" 5.7x28mm Barrel Specifications

• Caliber: 5.7x28mm
• Barrel Length: 5"
• Twist Rate: 1:9
• Profile: Medium Taper
• Material: 416 Stainless Steel
• Muzzle Thread: 1/2x28
• Gas Port Location: N/A
• Finish: Salt Bath Nitride
• Operating System: CMMG Radial Delayed Blowback
• Kit Weight: 1 lb. 6 oz.

CMMG Radial Delayed Blowback System

The included BCG is designed to operate with CMMG's Radial Delayed Blowback system. Rather than using the conventional gas-operated system found on a standard 5.56 AR-15, the RDB design uses a rotating bolt and delayed action.

Because this is an RDB configuration, the barrel does not require a conventional AR-15 gas port or gas system.

Lower & Magazine Compatibility

CMMG specifies its 5.7x28mm Barrel and BCG Kits for use with either:

• CMMG Mk57 lower receiver, or
• A compatible standard AR-15 lower receiver using CMMG 5.7 AR Conversion Magazines

Magazine and receiver compatibility should always be verified for the specific configuration being used.

What is the difference between the CMMG 5" and 8" 5.7x28 barrel and BCG kits?

The primary difference is barrel length and overall configuration. The CMMG 5" kit is designed around an ultra-compact 5.7x28 setup, while the 8" version provides three additional inches of barrel length. Both use CMMG's Radial Delayed Blowback operating system, a 1:9 twist rate, 416 stainless steel barrel construction, and 1/2x28 muzzle threads. The 5" kit weighs approximately 1 lb. 6 oz., compared with 1 lb. 10 oz. for the 8" kit.

Product Highlights

CMMG | 5.7x28mm | 5" Barrel | 1:9 Twist | Medium Taper | 416 Stainless Steel | 1/2x28 Threads | Salt Bath Nitride | Radial Delayed Blowback | Barrel + BCG Kit | 1 lb. 6 oz.