CMMG’s New Mk17 AR Runs SIG P320 Magazines: Powered by Radial Delayed Blowback

Visit CMMGInc to learn more about the Mk17.

CMMG has revolutionized the AR platform with its patented Radial Delayed Blowback operating system. CMMG’s new Mk17 is the latest variant of its AR-based pistol-caliber carbines and pistols, and the Mk17 uses SIG P320 magazines! This is not just another 9mm Colt clone.  

CMMG began in central Missouri in 2002 with a group of passionate shooters committed to quality. They have built a reputation on attention to detail, innovation, and craftsmanship. They make high-quality AR rifles in America and source all their own parts.

I was an earlier adopter of pistol-caliber carbines such as the Colt SMG, the MP5 and even the Ruger Police Carbine. The Mk17 is a mature design, better than anything that came before. The Colt pattern mags used by other guns had more than their share of problems. The Mk17 runs great with SIG P320 magazines of all capacities.

(Photo; CMMG)

Pistol-caliber ARs are cheap plinkers and great training tools for new shooters. You can safely shoot handgun steel and use the magazines you already have. Law Enforcement agencies can build an AR that accepts their duty pistol magazines for the ultimate police patrol rifle.

The Mk17, chambered in 9mm, uses, as mentioned, M-17/P320 magazines. The Mk17 is available in both BANSHEE (pistol) and RESOLUTE (rifle) configurations. Pair the BANSHEE or RESOLUTE with your existing M-17/P320 and you have the convenience of magazine interchangeability.

CMMG’s free-float handguard has a full-length Picatinny top rail for optics with M-LOK slots along the 3, 6, and 9 o’clock positions. The M-LOK system allows users to attach a variety of accessories to the handguard without the weight and sharp edges of unused rail sections.

Every branch of the U.S. armed forces, including Space Force and Coast Guard, have adopted SIG’s M-17 or M-18 service pistols. In November of 2019, SIG delivered its 100,000th M17/M18 handgun to the U.S. military. Working through the challenges of 2020, SIG is still cranking them out and the number continues to rise.

These M-17s and M-18s all come with magazines and soon there will be contracts for replacement magazines. Soldiers are rough on magazines. Industry powerhouses like ETS, Check-Mate and KCI USA have their own versions and others are coming out with theirs in the near future.

Good news: if you have a P320 or M-17/18. Soon magazines will be plentiful and affordable and now you have a personal defense firearm (PDW) that uses the same mags as your trusty handgun.

The heart of the Mk17, CMMG’s delayed blowback system, uses a two-piece bolt and bolt carrier. Like blowback bolts, the bolt key is only there to grab the charging handle, but after that, things get weird. Although it appears to have a standard AR-15 bolt carrier group, the Mk17 bolt is different in some important ways.

CMMG developed Radial Delayed Blowback (RDB) to handle the recoil of .45 ACP, the first caliber introduced in the RDB series.  The recoil impulse of .45 ACP didn’t lend itself to merely adding additional weight to the carrier and buffer, it needed something different and RDB was their innovative solution.

As the recoil impulse travels into the bolt and bolt carrier, the bolt must rotate before it can clear the locking lugs. As it rotates, the bolt cams against the weight of the bolt carrier and buffer, which keeps the action closed until the pressure drops, then it cycles like a standard AR.

The EOTech EXPS2 Holographic Sight is perfect for the Mk17 with a ring reticle with 2 dots. It features easy to adjust side buttons, a quick detach lever, and offers 2-eyes-open shooting. The TLR RM2 1000 Lumen Weapon Light sits below the EOTech line of sight. The tail switch supports easy manipulation.

With this system in place, the Mk17’s bolt and buffer are lighter than those in direct blowback guns which means less felt recoil. The combined difference in weight of the bolt carrier group and buffer, comparing straight blowback to Radial Delayed Blowback, can be as much as 6.5 ounces. CMMG offers an Action Tuning Kit that you can use to adjust the bolt weight, which allows users to tune the gun for use with different ammo and suppressors.

I tried several lights on MK17, the Streamlight TLR RM 2 is my favorite. With 1000-lumen, shock-proof LED technology, RM 2 provides 1.5 hours of runtime on two CR123 lithium batteries. This light is low-profile with a powerful beam that has an extensive range, good peripheral coverage, and a selectable strobe mode. I prefer the ergonomic multi-function tactical tail switch but there is also a remote switch included.

Another feature of the Mk17 is a real bolt hold open, something many pistol-caliber ARs lack. This speeds up reloads and permits standard AR manipulation. Mk17’s bolt hold open uses a dual-pinned, fully machined bolt catch linkage that uses a standard bolt catch spring. It works every time.

My favorite feature on the Mk17 is the RipStock (RipBrace for Mk17 pistols). This system provides a retractable buttstock (or adjustable brace) engineered for fast one pull deployment to your personal setting. With Fastback Technology, you simply pull straight back to extend. No locking tabs to bind. P3 Technology (Personal Position Preset) allows you to adjust the indexing screw and to set your own custom preset.

Some Pistol Caliber Carbines are funny about hollow point ammo. This is a significant issue if you are considering one for home defense. After testing it with a wide variety of ammo, I would not hesitate to use the Mk17 for protection.

I shot the following ammunition with no issue:

  • Armscor 115-grain full metal jacket
  • Speer Gold Dot 124-grain jacketed hollow point
  • Sig Elite V-Crown 115-grain jacketed hollow point
  • Sig Elite V-Crown 124-grain jacketed hollow point
  • Sig Elite V-Crown 147-grain jacketed hollow point
  • Winchester Black Talon 147-grain jacketed hollow point

I tried several different sights, but most of the shooting was done with my faithful old EO-Tech Holographic Sight. Taking a head-sized target at 25 yards is simple with the Mk17. Shooting 3-inch groups standing unsupported was also easy.

At 50 and 100 yards there were a couple of inches of drop and the groups grew to 6 inches. With magnified optics and good ammo you could get effective groups at 200 yards.

You can do drills with dueling trees, plate racks, Texas Stars and other targets that would not be safe to shoot with rifle calibers and boy is it fun. One thing you quickly figure out shooting the same drills with a handgun and a pistol-caliber carbine is how much faster the carbine is. On most drills, the time is cut in half. This translates directly into the real world. 

The Mk17 is ultra-reliable. I fired over 500 rounds of varied 9mm from my Mk17 with no cleaning.  It ran everything I fed it. Accuracy? While not designed for long-range, I had no issue ringing steel at 100 yards.

The Mk17 is offered in the BANSHEE configuration of AR pistols and short-barreled rifles with barrel lengths of 5” or 8” and the RESOLUTE rifle configuration with a 16-inch barrel. Both the BANSHEE and RESOLUTE offer last round bolt hold open.

The Grey Man Tactical Vehicle Rifle Rack is a perfect way to carry and mount your Mk17. Add a Ten Pack Magazine Storage and a Yellowstone Trauma Kit from and you are ready for anything on the range or the street. Fits in the safe and keeps everything together for a quick load out.

The Mk17 does everything well and the quality is among the best in the industry. It is fun and effective in any role. Over the years, I have shot most every rifle shaped platform that chambers 9mm. Whatever your application, the Mk17 in is a great option. I would not hesitate to use the Mk17 for home defense, in a pistol-caliber carbine competition or as a plinker to train AR skills at 9mm prices. Worried about terminal ballistics? A 124-grain jacketed hollow point has all the energy transfer you need for urban predators.

Each Mk17 ships with one 21-round magazine and a retail price ranging from $1,199.95 to $1,549.95 for the BANSHEE and $1,299.95 to $1,799.95 for the RESOLUTE (depending on series).

On all CMMG BANSHEE and RESOLUTE 300 Series firearms, consumers can choose from ten Cerakote colors at no additional cost. Both the 100 and 200 Series offer Cerakote for the complete firearm for an additional $150 per model.

(Featured Image by Mark Miller. CMMG Mk17 with Premier body armor, Safariland 7360RDS holster, sling and sling mounts. EOTech EXPS2 Holographic Sight , Streamlight TLR-8G 500 Lumen Compact Weapon Light, SIG ammunition and SIG P320RX with grip module.)

Visit CMMGInc to learn more about the Mk17.

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About the author: Mark Miller is a former Customs Agent and a Green Beret who served in Afghanistan and a number of other live fire locations. A student of firearms and shooting, he is an FFL and a SOT. The guiding philosophy of his life is that terrain and situation dictate tactics and the enemy always gets a vote on any plan.

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