Pistol caliber carbines are one of the hottest items on the market right now, which puts the gun you're reading about in a weird space. Technically, there's nothing special about it—the CMMG Mk17 Banshee is just a pistol caliber...pistol that takes SIG Sauer P320 magazines. The reason it's a pistol and not a short barreled rifle is because it's equipped with CMMG's RipBrace, which is designed to be strapped around the shooter's dominant arm to help stabilize the gun during single-handed firing.
The Mk17 from CMMG is the latest in their lineup of PCCs and pistols that use their proprietary Radial Delayed Blowback system. Using this system in a 9 mm PCC gives a significantly softer recoil impulse than you'd see with a straight blowback carbine such as the Beretta PX4 Storm. Straight blowback guns have to have heavy bolts by design, but with the Radial Delayed Blowback, the bolt carrier group can be similar in mass to a regular M4 bolt. Less mass equals less felt recoil on the shooter, less felt recoil equals faster follow up shots.
This Mk17 is the Banshee model with a 5-inch barrel, designed to fill the Personal Defense Weapon role and share magazines with your primary sidearm, in this case the Sig M17/M18/P320. It's available as a pistol or a short barreled rifle; this review features the pistol model using the RipBrace mentioned above.
In this pistol/SBR configuration, shooting the gun fast is...very easy. How fast? Working the classic Bill Drill from the low ready on a steel target, the CMMG Mk17 could get six hits in 1.10 seconds from the low ready, which with a reaction time of 0.35 seconds means the average split (time between shots) was about 0.15 seconds. For reference, that's a rate of fire of 400 rounds per minute, which is the same as the full auto rate-of-fire of an M3 Grease Gun.
You could ask what's the point of a gun like this, which is a fair question. With a 5-inch barrel you're not getting a ballistic advantage over a pistol like you would with a lever-action firing .357 Magnum; what you're getting is a firearm that's much easier to get hits with at intermediate ranges. It's also more inherently accurate than a regular pistol, and this particular Mk17 Banshee is far more accurate than a commercial model M18 that I had recently tested.
The Mk17 shot a group that measured 0.87 inches at its widest point using factory ammo at 25 yards. From a practical standpoint, a gun like this can live in a backpack or other small bag, but gives decisive engagement ability out to 50+ yards for even a casual user.
I set this gun up with a Holosun 507c that I had lying around, and a mount I quite literally found in that bin full of random gun parts that every firearms journalist has. Zeroing at 25 yards was a piece of cake with Federal 124-grain HST +P. Rounds tested included Magtech 115-grain FMJ, Federal Premium 150-grain Syntech, two different grain weights of Federal HST, Hornady Critical Defense, and some random FMJ.
During the evaluation phase of 500 rounds, the gun didn't choke once. It kept shooting and shooting. Its favorite round, and my favorite as the shooter, was the 150-grain Syntech. The subsonic bullet was so quiet and so soft shooting it felt like shooting a suppressed gun.
Another advantage to the Mk17 Banshee in pistol format is exactly that: it's a pistol. That means assuming you have a concealed firearm license or live in a Constitutional Carry state, it's legal to conceal this gun. That goes back to the backpack idea for a travel gun that pairs with your EDC. Say you carry a Sig P320 variant for your EDC, but you're traveling and in these uncertain times you want something that can reach out a little further than your pistol. Enter the Mk17 Banshee. With a red dot sight and good ammo, 50 meters is now easily within range. This gun could push to 100 with 124 grain +P hollowpoints.
Of course, all that is a lot of justification for something that needs no justification, because the bottom line on the Mk17 Banshee is that it's hilariously fun to shoot. In an afternoon, I shot this gun more than I shot my 5.56 AR-15 in the two years that I owned the rifle, because the Mk17 Banshee is more fun. It was fun to shoot Bill Drills, it was fun to shoot groups, it was fun to see how fast I could react to the buzzer, it was just a blast. I spent at least 15 minutes trying to see if I could get 10 shots off under 2 seconds, and came close a couple of times.
Normally, this would be the part of the article where I tell you what I don't like about the gun. I can't, because I like everything about this gun. It can be used for serious work, but it doesn't take itself too seriously. The trigger is nice, the barrel is threaded for attachments, the grip is Magpul, I like the brace because it's useful and functional; I even like the midnight bronze color. It sort of color matches my M18. It's not even that expensive, the MSRP on the five-inch pistol model is $1,549.95. Under 1,600 bucks for a pistol that shares mags with your carry pistol but is easier to shoot sounds like a steal to me.
It's rare that a gun comes along that I can't find something to nitpick about, but CMMG hit this one out of the park. It's fun to shoot, it's reliable, it makes sense from a practical standpoint, and if you don't want it as a PDW or SBR, you can also get the Mk17 with a full-length barrel as a regular PCC to shoot in IDPA or USPSA. But to me, a 16-inch rifle isn't going to leave a smile on your face like this little gun does. The Mk17 Banshee is an absolute home run, and I don't think I'm going to send this one back.