AR15 12.5" 300BLK Mr Barrel

Name: AR15 12.5" 300BLK Mr Barrel
Brand: CMMG
Availability: InStock

CMMG · Barrels

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Best price

$181.99at Ammunition Depot

In stock Lowest in 30 dayschecked Nov 4, 2026

Buy at Ammunition Depot

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Fits and works with

Caliber: 300 Blackout · Shop matching ammo
Bolt: Standard AR-15 (5.56 / 300 BLK / .350 Legend) · Bolt carrier groups
Muzzle thread: 5/8x24 · Muzzle devices
Barrel length: 12.5" · Handguards

Specifications

Manufacturer: CMMG
Color: Black
Platform: AR-15
Caliber: 300 Blackout
Barrel length: 12.5"
Thread pattern: 5/8 x 24

Where to buy

Store	Price	Availability	Buy
Ammunition Depot Best price	$181.99checked Nov 4, 2026	In stock	Buy at Ammunition Depot
Brownells 17.76% off · ends Nov 15 · exclusions apply	$215.38checked Nov 13, 2026	In stock	Buy at Brownells
CMMG	$199.95checked Nov 13, 2026	Check store	Buy at CMMG
Palmetto State Armory	$203.99checked Nov 2, 2026	Check store	Buy at Palmetto State Armory
OpticsPlanet	$193.49Salechecked Nov 13, 2026	Out of stock	Buy at OpticsPlanet
MidwayUSA	$197.99checked Nov 13, 2026	Out of stock	Buy at MidwayUSA

Prices and availability change often, so confirm on the store's site before you buy. We may earn a commission from these links.

Price history

Show

Lowest in-stock price in the last 30 days: $181.99 at Ammunition Depot. Dashed line = out of stock. Tracking since Sep 27, 2026.

Show the prices as a table

Store	Latest	Lowest	Highest
Ammunition Depot	—	$181.99	$181.99
Brownells	$215.38	$215.38	$215.38
CMMG	$199.95	$199.95	$199.95
MidwayUSA	$197.99	$192.99	$197.99
OpticsPlanet	$193.49	$193.49	$193.49
Palmetto State Armory	—	$192.99	$212.99

Since Sep 27, 2026.

About this part

The AR15 12.5" 300BLK Mr Barrel is a 12.5" 300 Blackout barrel from CMMG. It's sold by 6 stores (2 in stock), from $181.99 to $215.38. The lowest in-stock price in the last 30 days was $181.99 at Ammunition Depot.

From the manufacturer

Direct replacement for the standard .223/5.56mm barrel converts your AR-15 to the high-performance 300 AAC Blackout (300BLK) cartridge. The 300 AAC lets you upgrade your rifle to 7.62 x 39 ballistics, while retaining the standard AR-15/M16 bolt, carrier, and magazine at its full capacity, with no additional modifications. 1-7" rifling accepts bullet weights from 110 gr to 220 gr, and 5/8"-24 muzzle threads accept popular AR-.308 flash suppressors and muzzle brakes. Three models available, 16", 12.5" and 8.2" long and treated inside and out with CMMG's "Wasp" nitriding process for outstanding resistance to wear and corrosion. 16" barr Mfg: Cmmg SPECS: Hardened 4140 chrome-moly steel, Wasp nitride finish, matte black .750" O.D. at gas port.5/8-24 muzzle threads.