TFB Review: CMMG Mk17 – SIG P320 Mag Compatible PCC

The CMMG Banshee/Resolute line of PCCs is one of the more impressive systems that has come out lately. Instead of being straight blowback, it is a radial delayed blowback system. This enables the Banshee to be able to withstand higher pressure cartridges like 10mm Auto, and have softer felt recoil and less gas to the face than a conventional blowback firearm would. Previously compatible with Glock, Colt SMG, and FN Five-seveN magazines, the Banshee/Resolute line has a new series compatible with SIG P320 magazines: The Mk17.

Per CMMG:

CMMG spent years innovating the AR platform with the patentedRadial Delayed Blowback operating system that has revolutionized the industry. The addition of the Mk17, chambered in 9mm, shows CMMG’s commitment to never settling. Accepting Sig Sauer™ M17/P320™ magazines, the Mk17 is available in both BANSHEE and RESOLUTE configurations. Pair the BANSHEE or RESOLUTE with your existing M17/P320 and you have the convenience of magazine interchangeability.

Staying true to its innovative and industry-leading values, CMMG brings to market the Mk17 on the heels of the U.S. Army and Marine Corps adoption of the Sig Sauer M17/M18™ service pistols. In November of 2019, Sig Sauer delivered its 100,000thM17/M18 handgun to the U.S. military and the number continues to rise. Those familiar with the platform now have a personal defense firearm (PDW) at their disposal. As hundreds of thousands of service members adopt a new pistol platform over the next 20-30 years, the CMMG Mk17 will be a great pairing to add to their arsenal.

For personal defense, the Mk17 is offered in the BANSHEE configuration of AR pistols and short-barreled rifles with various barrel lengths. For the competitive shooter, the Mk17 comes in CMMG’s RESOLUTE line of 16-inch barreled rifles.

The BANSHEE is offered as a pistol or short barreled rifle with barrel lengths of 5” or 8”, while RESOLUTE rifles comes with a 16” barrel. Both the BANSHEE and RESOLUTE offer Last Round Bolt Hold Open.

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.

For more information on the Mk17, please visit CMMGinc.com/Mk17.

• CALIBER: 9×19
• BARREL: 5″ MT 4140CM SBN, 9mm
• MUZZLE: Thread Protector, Threaded ½-28
• RECEIVER: Forged 7075-T6 AL Lower, Forged 7075-T6 AL Upper
• HAND GUARD: CMMG RML4 M-Lok hand guard
• FINISH: Cerakote Standard
• CHARGING HANDLE: CMMG Oversized Ambi
• PISTOL GRIP: Magpul MOE
• PISTOL BRACE: CMMG Micro/CQB RipBrace with 5 Position Fastback Receiver Extension and Ambi Sling Plate
• TRIGGER: CMMG Single stage mil-spec style trigger
• TRIGGER GUARD: Integrated Into Lower
• SAFETY SELECTOR: CMMG Ambi
• MAGAZINE: P320 21rd
• WEIGHT: 4lbs 10oz(unloaded)
• LENGTH: 18.9″ (brace collapsed)

I somewhat knew what to expect, having previously reviewed a few 5.7mm CMMG’s and owning a 10mm model.

The CMMG Banshee 300 (all the bells and whistles) Mk17 shipped in a cardboard box with a 21 round SIG P320 magazine. Finished in CMMG’s Titanium Cerakote, the Banshee Mk17 exhibited excellent fit and finish right out of the box. Trigger pull on my example averaged out at 5lbs, 5oz. Most Mk17s come with CMMG’s single stage trigger, although the Resolute 300 rifle will come with a Geissele SSA 2-stage. The 21 round SIG M17/18/P320 magazine easily and positively inserted, and dropped free with every press of the mag release.

My example also included CMMG’s “Fastback” receiver extension, which allows for a more rapid deployment of the brace from collapsed to one’s preferred position. Paired with CMMG’s “Ripbrace”, it made for a very stable third point of contact with the firearm. As with other short Banshees, the Mk17 has an excellent integrated hand stop shelf at the end of the handguard. The 5″ barrel example has a thread protector, though longer barrel lengths come with an SV brake or an A2 comp.

After mounting a spare RDS, I headed out to the range with the Mk17 and my “variety box” of 9mm. Consisting of over 15 different loads of all pressures, primers, case materials, and bullet profiles, the variety box is what I use to find a 9mm platform’s weakness. As far as reliability goes, the CMMG Mk17 passed with flying colors. Not a single malfunction occurred in over 400 rounds fired, both unsuppressed and suppressed. This includes Israeli SMG ammunition from the 1970s, known for very hard primers.

The last round bolt hold open function worked every single time with the two P320 magazines I used during testing. Magazine changes were quick and easy to master with little practice. The magazine well guides the magazines in easily, and they clicked positively into place regardless of being fully loaded or if the bolt was closed or open. The SIG P320 magazines also presented the rounds at a pretty optimal angle for chambering. All in all, I was very pleased with the system’s reliability.

As many PCC users prefer to shoot with the aid of a silencer, I mounted an old Gemtech Blackslide I had available to me to the Mk17. Though not totally appropriate for caliber, it still reduced the noise quite a bit, especially with the 150gr Syntech loads. There was no noticeable gas to the face either, thanks in part to the radial delayed blowback system. As to be expected, however, the receiver was slightly dirtier due to the use of the suppressor, and there was a bit of carbon/gas residue on the top portion of the P320 magazines.

The CMMG Mk17 performed flawlessly throughout the course of my testing. Accuracy, fit and finish were excellent. Why buy one of these over a Glock magazine compatible PCC? The obvious answer is that it is built from the top down to run with SIG P320/M17/M18 magazines. If one primarily uses any SIG P320 platform and has a surfeit of such magazines, it would make sense to take a good look at the Mk17 for PCC use. Besides the Matador Arms magwell adaptor, the Mk17 is one of the few such systems available compatible with P320 magazines. Variety and options are always a good thing, and the CMMG Mk17 provides the shooting public with more of both. If you are a P320 devotee interested in getting into a top-shelf PCC, give the CMMG Mk17 line a good look.