338 ARC Rifles & Systems

338 ARC Rifle Systems from Chattahoochee Munitions

The 338 ARC Rifle lineup from Chattahoochee Munitions approaches the cartridge through two distinctly different firearm platforms: the CM15 semi-automatic AR-15 and the CM7S bolt action.

One of the defining characteristics of 338 ARC is its ability to bring heavy .338-caliber projectile capability into the smaller AR-15 cartridge envelope. At the same time, the cartridge is equally interesting in a compact bolt-action platform, particularly for shooters interested in heavy subsonic ammunition and suppressed applications.

Rather than building every 338 ARC Rifle around a single specification, Chattahoochee Munitions configures each system around its intended role. Barrel length, twist rate, magazine selection, ammunition, suppressor use, and—in the CM15—gas and buffer adjustment are all considered as parts of the complete firearm.

The cartridge is standardized by the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI), establishing the dimensional and pressure specifications around which commercial 338 ARC firearms and ammunition are designed.

CM15 338 ARC Rifle – The AR-15 Platform

The CM15 338 ARC Rifle combines the compact AR-15 platform with the versatility of the .338-caliber ARC cartridge.

CM currently offers the CM15 in 16-inch, 10.5-inch, and 8.5-inch barrel configurations. The 16-inch rifle uses a 1:8 twist, while our shorter 10.5-inch and 8.5-inch configurations use faster 1:5 twist barrels based on Chattahoochee Munitions’ experience with heavy .338-caliber projectiles and subsonic applications.

Adjustable gas and an adjustable buffer system are standard components of the CM15. This allows the operating system to be configured around the ammunition, barrel length, suppressor use, and intended application rather than treating every configuration identically.

The shorter CM15 configurations trade some potential ballistic efficiency for reduced overall firearm length. That can become particularly valuable when a suppressor is added to the system.

For shooters who specifically want an AR-15-based 338 ARC Rifle, the CM15 provides three distinct approaches to the cartridge rather than a single barrel configuration.

Every CM15 338 ARC firearm is supplied with a magazine configuration tested and vetted by Chattahoochee Munitions.

CM7S 338 ARC Rifle – The Bolt-Action Platform

The CM7S 338 ARC Rifle takes a different approach.

Built around our Remington 700-footprint CM7S action, the bolt-action platform eliminates the requirement to use propellant gas to cycle a semi-automatic operating system. This makes the CM7S particularly interesting for compact suppressed and heavy-subsonic configurations.

Chattahoochee Munitions currently offers CM7S 338 ARC firearms with 16-inch, 12.5-inch, and 8-inch barrels.

Unlike the CM15 lineup, all CM7S 338 ARC barrel lengths use a 1:5 twist. That is an intentional CM specification based on our experience with heavy .338-caliber projectiles, including the Hornady 307-grain Sub-X.

The result is a 338 ARC Rifle that retains the compact cartridge architecture while approaching subsonic and suppressed use from a manually operated platform.

The CM7S uses a 6.5 Grendel Type II bolt face and an AICS-pattern magazine system. Complete firearms are supplied with the magazine configuration tested and selected by Chattahoochee Munitions for the platform.

Choosing a 338 ARC Barrel Length

There isn’t one ideal barrel length for every 338 ARC Rifle because maximum velocity is not always the primary objective.

Barrel length changes the character of a 338 ARC Rifle considerably. A conventional 16-inch rifle, a 12.5-inch bolt action, and an 8-inch compact configuration can share the same cartridge while serving very different purposes. CM therefore treats barrel length as part of the overall system rather than assuming the longest barrel is automatically the best choice.

In Chattahoochee Munitions testing and loading experience with the configurations we have evaluated, powder utilization occurs around the 12-inch range. That makes approximately 12 inches an especially useful point in the cartridge’s performance envelope.

A 16-inch barrel provides a conventional rifle configuration and is particularly attractive to customers who do not want a short-barreled firearm.

The 12.5-inch CM7S offers a balance between compact overall dimensions and efficient use of the cartridge based on our experience.

Shorter 10.5-inch, 8.5-inch, and 8-inch configurations prioritize compactness. Some potential velocity and powder utilization are exchanged for a shorter firearm, which can be particularly advantageous when overall system length includes a suppressor.

The appropriate choice ultimately depends on what the rifle is intended to accomplish.

338 ARC Barreled Actions

Chattahoochee Munitions also offers the CM7S as a 338 ARC barreled action for customers who want to select their own stock or chassis system.

Current CM7S barreled-action configurations include:

• 16-inch
• 12.5-inch
• 8-inch

Each uses the CM7S action architecture and the same 1:5 twist philosophy found throughout our complete CM7S 338 ARC lineup.

This provides another route into the 338 ARC Rifle platform for customers who want CM’s action and barrel configuration while selecting their own stock or chassis system.

Tested 338 ARC Magazines

Magazine compatibility is part of the firearm system at Chattahoochee Munitions. We do not expect the customer to purchase a rifle and then experiment with magazines to determine what works.

CM15 firearms use our 338 ARC AR15 Magazine, a 10-round stainless-steel DURAMAG tested and vetted by Chattahoochee Munitions for 338 ARC operation. For optimal feeding and reliable operation, Chattahoochee Munitions recommends loading the magazine with no more than eight rounds.

CM7S firearms use our 338 ARC Bolt Action Magazine, a 10-round MDT polymer AICS-pattern magazine tested by Chattahoochee Munitions with 338 ARC, 6 ARC, and 22 ARC.

Complete CM 338 ARC firearms are supplied with the appropriate tested magazine.

338 ARC Subsonic and Suppressed Applications

For many customers, suppressed operation is one of the primary reasons for considering a 338 ARC Rifle in the first place.

Subsonic capability is an important part of what makes 338 ARC interesting, but there is considerably more to building a successful subsonic system than simply selecting a heavy projectile.

Twist rate, projectile construction, barrel length, action type, magazine configuration, ammunition, and suppressor use all influence the complete system. In a semi-automatic firearm, gas and buffer configuration add additional variables.

Hornady’s 307-grain Sub-X is one of the heavy subsonic projectiles around which Chattahoochee Munitions has evaluated its faster-twist 338 ARC configurations.

We’ve covered these subjects separately in our 338 ARC Subsonic technical guide, including 1:8 versus 1:5 twist rates, barrel length, suppression, subsonic versus supersonic ammunition, and comparisons with both 300 Blackout and 8.6 Blackout.

If you’re researching the cartridge before selecting a rifle, that is the place to start.

Why CM Builds More Than One 338 ARC Rifle

A conventional 16-inch AR-15, an 8.5-inch semi-automatic, a 12.5-inch bolt action, and an 8-inch bolt action are very different firearms even though they share the same chambering.

That’s intentional.

Chattahoochee Munitions specializes in less-mainstream cartridges and suppressed firearm systems. Our experience with heavy .338-caliber projectiles has shown us that there is little reason to force every application into the same configuration.

The objective is not simply to chamber another firearm in 338 ARC. It is to build the 338 ARC Rifle around the role it is intended to perform.

Whether that means a conventional CM15, an exceptionally compact semi-automatic, a CM7S bolt action, or a barreled action serving as the foundation for a custom configuration, Containment Zone 338 brings the complete Chattahoochee Munitions 338 ARC lineup together in one place.