CMMG 9mm 8" Barrel and BCG Kit Radial Delayed Blowback - 99D517A

CMMG 9mm 8" Barrel and BCG Kit (Radial Delayed Blowback System) - 99D517A - UPC 815835019802

Product Description

The CMMG Radial Delayed Blowback (RDB) 9mm Barrel and Bolt Carrier Group Kit (99D517A) is a revolutionary drop-in performance system designed to build or convert an AR-15 platform into a soft-shooting, high-reliability 9mm pistol-caliber carbine (PCC). Unlike traditional direct blowback 9mm setups that require heavy recoil buffers and stiff springs, CMMG's patented Radial Delayed Blowback mechanical system uses angled locking lugs on the bolt face that momentarily delay rearward bolt travel until chamber pressure drops to safe levels.

This innovative mechanical delay dramatically reduces felt recoil, mitigates gas blowback when shooting suppressed, and allows builders to utilize standard AR-15 carbine buffers and buffer springs rather than specialized ultra-heavy blowback weights. The kit includes an 8.0-inch medium-taper barrel machined from 4140 chrome-moly steel with a durable Salt Bath Nitride (SBN) finish, featuring a 1:10" twist rate and standard 1/2"-28 threaded muzzle for muzzle devices or suppressor mounts.

Paired directly with CMMG's proprietary Radial Delayed 9mm Bolt Carrier Group, the 99D517A kit allows custom builders to assemble custom 9mm AR uppers using standard Mil-Spec AR-15 upper receivers. Compatible with CMMG MkG (Glock-style) lowers, MkGs lowers, or standard AR-15 lowers paired with CMMG 9mm ARC30 conversion magazines, this barrel and BCG kit delivers match-grade soft recoil and incredible reliability for PCC competition, personal defense, and suppressed range staging.

*Armorer Bench Notes & Real-World Staging Guidance:

Fitment Matrix: Installs into standard Mil-Spec AR-15 upper receivers. Optimized for use with CMMG MkG / Mk9 lower receivers or standard AR-15 lowers using CMMG 9mm ARC 30-round conversion magazines. Note: Requires an upper receiver with an enlarged ejection port (standard AR-15 upper or 9mm PCC upper works; do not use non-standard narrow-port uppers).

1. Verify host upper receiver is completely clear, safe, and clean before barrel installation.
2. Install the 8.0" 9mm barrel into the upper receiver barrel extension socket, apply anti-seize to threads, and torque barrel nut to 35–50 ft-lbs per handguard manufacturer specifications.
3. Install the CMMG Radial Delayed 9mm BCG with standard AR-15 charging handle; pair host lower with a standard carbine buffer and spring (do NOT use heavy 9mm blowback buffers).

Key Features

• Patented Radial Delayed Blowback (RDB): Angled bolt lug mechanical delay reduces felt recoil and suppressor port noise significantly over traditional direct-blowback systems.
• 8.0-Inch 4140 CM Steel Barrel: Medium-taper profile with Salt Bath Nitride (SBN) finish for exceptional corrosion and wear resistance.
• Standard Buffer Compatibility: Works with standard AR-15 carbine buffers and tuning springs without requiring heavy 9mm buffers.
• 1/2"-28 Threaded Muzzle: Standard thread pitch accepts wide variety of 9mm muzzle brakes, flash hiders, and suppressor QD mounts.
• Versatile Lower Compatibility: Functions with Glock-pattern PCC lowers, Colt-pattern lowers, or standard AR-15 lowers using CMMG 9mm ARC mag conversions.

Product Specifications

• Brand: CMMG Inc.
• Model: 9mm 8.0" Barrel and BCG Kit (Radial Delayed Blowback)
• MPN / Part Number: 99D517A
• UPC: 815835019802
• Caliber: 9x19mm Parabellum / 9mm NATO
• Barrel Length: 8.0 inches
• Barrel Contour: Medium Taper
• Barrel Material: 4140 Chrome Moly Steel
• Barrel Finish: Salt Bath Nitride (SBN)
• Twist Rate: 1:10" Right-Hand Twist
• Muzzle Thread: 1/2"-28 TPI
• BCG System: CMMG Radial Delayed Blowback (RDB) 9mm Bolt Carrier Group
• Mass: ~2.1 lbs (952.5 g)