First Look: CMMG 5.7x28 mm AR Conversion

by
posted on January 15, 2020
** When you buy products through the links on our site, we may earn a commission that supports NRA's mission to protect, preserve and defend the Second Amendment. **
cmmg-inc-57x28mm-ar-conversion-magazine-upper-receiver-f.jpg
In 2020, the 5.7x28 mm cartridge is coming back in a big way, and CMMG joined multiple companies in offering a new option for fans of this high-velocity cartridge. Following up on the success of the company's Banshee chambered in 5.7x28 mm, CMMG now offers an AR-15 conversion package that allows shooters to mate their mil-spec AR-15 lower receiver with the company's 5.7x28 mm Radial Delayed Blowback upper-receiver group.

The key to this conversion lies in CMMG's 5.7 AR Conversion Magazine, which is designed to fit into standard AR-15 magazine wells while providing a reliable feed mechanism that's compatible with the company's 5.7x28 mm upper receiver. To convert any standard AR-15 to a 5.7 mm firearm, simply remove the existing upper-receiver group and replace it with a compatible, 5.7x28 mm upper receiver from CMMG. Once the upper receiver is installed, users can simply insert a CMMG 5.7 AR Conversion Magazine into the mil-spec magazine well.

In addition to allowing AR owners to experiment with the 5.7x28 mm cartridge without having to purchase an entirely new firearm, this CMMG conversion system maintains the controls and configuration of any existing AR-15 lower. If users have an enhanced trigger installed in their gun or optimized controls, they can continue using those components without having to invest in or learn an entirely new firearm. CMMG recommends the use of a standard carbine buffer and action spring to run the 5.7x28 mm conversion reliably, and the magazine provides last-round bolt hold-open capability.

A complete lineup of CMMG Banshee and Resolute upper receivers are compatible with the 5.7 AR Conversion Magazine. CMMG's Mk57 upper receivers can be had in 5", 8" and 16" barrel lengths, and the uppers ship complete with bolt-carrier group and charging handle. A single CMMG 5.7 AR Conversion Magazine holds 40 rounds of 5.7x28 mm, and the suggested retail price on the mag is $39.95. Suggested retail pricing on the Mk57 upper receiver complete with three 40-round magazines starts at $799.95. For more information on these conversion kits, visit cmmginc.com.


Latest

Gotw Rra Lar 22 Tactical Carbine Web
Gotw Rra Lar 22 Tactical Carbine Web

Gun Of The Week: Rock River Arms LAR-22 Tactical Carbine

This week, we're on the range with the Rock River Arms LAR-22 Tactical Carbine, a rimfire variant of the AR-15 that's designed for reliability and gives enthusiasts a way to shoot affordably.

The Armed Citizen® July 11, 2025

Read today's "The Armed Citizen" entry for real stories of law-abiding citizens, past and present, who used their firearms to save lives.

Japanese Last-Ditch Small Arms Of World War II

The crude assortment of fighting tools used by the Japanese during World War II give clues of an unprepared and unmatched last-ditch fight that ultimately lead to Allied victory.

Federal Ammunition Awards 2025 Tom Knapp Memorial Scholarships

Federal Ammunition recently awarded the 2025 Tom Knapp Memorial Scholarships to two 4-H shooting sports teen ambassadors.

2025 Optic Of The Year: Burris Eliminator 6

Even as new generation after new generation of Burris Eliminator continued to add more advanced technology and functionality, it remained odd-looking—until the launch of this year’s sixth-generation product, which is the first in the line that can mount atop a rifle using standard 34 mm scope rings.

I Have This Old Gun: Star Model B

Of the many Spanish-made firearms to emerge throughout the 19th and 20th century, one of the most recognizable is the Star Model B, largely due to its similarity to the Colt Model 1911.

Interests



Get the best of American Rifleman delivered to your inbox.