CMMG MK4 .300 AAC Blackout AR-15, 16 in Barrel, BCM KMR-A15 15 in Handguard, Geissele 3-Gun Trigger, NiB BCG
This custom CMMG MK4 in .300 AAC Blackout is a purpose-built AR-15 that combines a CMMG 16 in upper and MK4 lower with high-end components from BCM, Geissele, V Seven, Redi-Mag, and A*B Pro. It features a BCM KMR-A15 15 in free-float KeyMod handguard with a full-length, T-marked Picatinny top rail, a Geissele 3-Gun single-stage 3.25 lb trigger, an A*B Pro nickel-boron bolt carrier group, and extensive V Seven titanium small parts. The carbine-length gas system with a low-profile gas block, BCM 7.62 mm compensator, and Aukmont 45-degree backup iron sights round out a well-sorted, feature-rich build.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: There are significant signs of prior use and markings from previous handling. Please refer to the photos for detailed views of the surfaces and markings.
What’s Included
- Aukmont clamp-on backup iron sights (installed; front and rear)
- Bravo Company BCM KMR-A15 15-inch KeyMod free-float handguard (installed)
- BCM compensator/muzzle device (installed)
- Redi-Mag Redi-Release and Redi-Catch (installed)
- Magpul MOE SL-K collapsible stock (installed)
- ERGO pistol grip (installed)
- Short forward hand stop (installed)
- 1x 30-round Magpul PMAG polymer AR-15 magazine
Built on a CMMG MK4 lower with a CMMG upper and 16 in barrel, this rifle uses a direct-impingement system with a carbine-length gas tube and a low-profile gas block. The barrel is threaded and paired with a BCM 7.62 mm compensator. The BCM KMR-A15 15 in KeyMod free-float handguard provides extensive accessory mounting and a full-length, T-marked Picatinny top rail. A fitted barrel nut and a short forward hand stop are installed.
The fire control group centers on a Geissele 3-Gun single-stage trigger set at approximately 3.25 lb for fast, predictable breaks. Controls are further enhanced with Redi-Mag upgrades: the Redi-Release Quick-Release BAD and Redi-Catch bolt lock. A BCM Gunfighter charging handle with a left-side extended latch supports one-handed charging.
Reliability and durability upgrades include an A*B Pro nickel-boron coated bolt carrier group with a phosphate extractor, plus multiple V Seven titanium components: pivot and takedown pins, magazine release, sling attachment, firing pin, forward assist, and a 57-degree safety selector. An upgraded trigger guard is fitted, and the ejection-port cover features custom white text. The forged upper bears the "A" forge mark.
Sighting is handled by Aukmont 45-degree clamp-on backup iron sights. Furniture includes a Magpul MOE SL-K collapsible stock and an ERGO rubberized pistol grip. The receivers are aluminum with a hard-coat anodized finish. Capacity is 30+1 with the included PMAG, and the listed length of pull is 10.5 in.