TESTED: CMMG Resolute 6.5 Grendel Mid-Size AR with PowerBolt

Ever since I tried 6.5 Grendel, I’ve wanted to get hands-on with it here on Ultimate Reloader, and NOW is that time! In this article, I’ll give an in-depth overview of my new AR: the CMMG 300-series Resolute mid-size AR chambered in 6.5 Grendel. 6.5 Grendel is a fascinating cartridge, and the CMMG 6.5 Grendel AR rifles take a different approach with this cartridge. Interested? Read on!

6.5 Grendel: Compact 6.5 for the AR

6.5 Grendel enables an AR shooter to achieve similar ballistics to 308 Winchester from a 6.5 mm cartridge that can be utilized by rifles built on the AR-15 platform. Since the AR-15 is more compact and lighter in weight, an AR-15 in 6.5mm Grendel is an interesting alternative to the AR-10/LR308 type platforms. When I first picked up a 6.5mm Grendel cartridge, I thought- “Wow, that’s short and compact”. It’s actually derived from the 7.62x39mm cartridge, another popular chambering for the AR-15. By necking down the 7.62x39mm to 6.5mm, more velocity is attained from a similar powder charge.


Designed in 2003, he 6.5mm Grendel is a relatively new cartridge. The “short and compact” form factor is the result of the need for more powder capacity (compared with 5.56 NATO or .223 Remington) and to allow “room” for long slender high-BC bullet profiles. At the same time, the cartridge needs to fit into AR-15 length magazines. It’s a game of trade-offs, but the 6.5mm Grendel manages these trade-offs very well.

One Big Issue: The AR-15 Bolt

When you convert an AR-15 over to 6.5 Grendel, you need to change the bolt (utilizes the same bolt face as 7.62x39mm), the barrel, the magazines, and in some cases you’ll want a different gas system length, and even an adjustable gas block. The main problem with a typical AR-15 6.5 Grendel setup like this is the thin walls of the bolt after being “bored out” in diameter to accommodate the 6.5 Grendel case rim as shown in this picture:

PowerBolt To the Rescue

CMMG started work on the PowerBolt to solve similar thin-wall bolt issues for AR type rifles chambered in 7.62x39mm. The result was the MK-47 Mutant rifle which was designed on a “mid size” (between AR-15 and AR-10 length upper/lower receiver length) CMMG platform. This rifle was also designed to use AK-47 magazines without modification:

PowerBolt is a design whereby the bolt and bolt carrier are essentially the same as an AR-10 except about 3/4″ shorter. This results in a rifle with the bolt strength of an AR-10 with an overall length that’s significantly shorter than an AR-10. This is an ideal solution for cartridges that are too powerful for the weak thin-wall bolts resultant in AR-15 adaptations without the unnecessary bulk or weight of an AR-10 type rifle. Here’s a picture of PowerBolt next to an AR-15 bolt for 6.5 Grendel or 7.62x39mm:

You can see here how much stronger the PowerBolt is compared to the equivelent AR-15 bolt.

Here’s a picture showing a 223/5.56 bolt/carrier (top), CMMG’s PowerBolt for 6.5 Grendel (middle), and an AR-10 bolt/carrier (bottom): (click/tap to enlarge)

Gavin’s Resolute 6.5 Grendel Rifle

For my content covering 6.5 Grendel, I decided I wanted to compare and contrast an AR type rifle, and a bolt-action rifle. Unlike what I did for 224 Valkyrie (AR and bolt gun with same barrel specs) for 6.5 Grendel I decide to take two different approaches for rifles. The AR would be compact and ideally suited for hiking and things like target shooting or Coyote hunting. The bolt gun would be more focused on long-range shooting and testing ballistic capabilities for 6.5 Grendel (longer barrel, etc). So for the 6.5 Grendel AR, the decision was easy, go for the CMMG 300-series Resolute mid-size AR chambered in 6.5 Grendel. This rifle is top-quality, compact, and I hoped it would be accurate as well.

Here’s what’s shown in the unboxing photo above (included with rifle):

  • Box
  • Rifle
  • 10 round AR-15 compatible 6.5 Grendel magazine (1)
  • Sample bottle of Slip 2000 EWL
  • Instruction booklet
  • CMMG sticker

Above: the CMMG Resolute 300 6.5 Grendel setup for long-range shooting with:

  1. Athlon Midas TAC 6-24x50mm first focal plane scope
  2. Harris S-BRM 6-9″ bipod

Info and Specs

From the CMMG product page:

CMMG’s RESOLUTE lineup is engineered with purpose for those who refuse to compromise on quality. Each RESOLUTE rifle comes with a 16-inch barrel and is designed for balance, accuracy and maneuverability. The RESOLUTE lineup is available in three tiers —RESOLUTE 100, RESOLUTE 200 and RESOLUTE 300 — that cater to your intended needs and customization. Whether you’re defending your family or looking to bring out your best at the range, the RESOLUTE keeps going when you need it most. NOTE: The CMMG Mid-sized receivers for the “Mk47” and “MkW” firearms, uppers, and lowers are a hybrid AR platform. The CMMG Mid-sized receivers are NOT compatible with standard AR-15 (CMMG Mk4) or .308 WIN (CMMG Mk3) platforms.

CALIBER: 6.5 Grendel
BARREL: 16.1″, 1:8 twist, Medium Taper, 416SS, SBN
MUZZLE: CMMG SV Brake, threaded 5/8-24
RECEIVER: Billet 7075-T6 AL Mid Size upper, Billet 7075-T6 AL Lower
HAND GUARD: CMMG RML15 M-Lok hand guard
FINISH: Cerakote Receivers and Hand Guard
BUTT STOCK: CMMG RipStock with 6 Position Enhanced Receiver Extension and Ambi Sling Plate
TRIGGER: Geissele Automatics SSA 2-Stage
TRIGGER GUARD: Integrated Into Lower
MAGAZINE: 10rd 6.5 Grendel Magazine
WEIGHT: 8lbs 4oz(unloaded)
LENGTH: 33.3″(stock collapsed)

A Look Down the Bore

When I used my Lyman Borecam Borescope to look down my Resolute’s bore, I was surprised! CMMG does not list the Resolute as having a match-grade barrel, but from the inside, mine looks very much like one. This is great becase all else being equal, the rifle should shoot better. It also should require less cleaning compared to a rifle with a less-smooth bore. After several hundred rounds through the rifle and two cleanings, I can say this rifle seems to collect very little carbon or copper. For accuracy results, keep reading.

TriggerScan Results

The DVORAK TriggerScan TS-11 is a device that profiles any firearm’s trigger by creating a force-distance graph. The TriggerScan software also performs calculations for things like take-up, creep, travel to actuate, and peak force. Here’s the TriggerScan graph for the CMMG Resolute 6.5 Grendel with Geissele SSA AR-15 trigger: (click/tap to enlarge)

Here are the results from this testing (three passes averaged):

Peak force 4.278″
Travel to actuate 0.091″
Takeup 0.070″
Overtravel 0.047″

You can see from the TriggerScan graph that this trigger has a very consistent trigger pull, and the break is well-suited for general use, and long-range shooting if you are practiced up with it. A very clean two-stage trigger!

First 6.5 Grendel Loads

To start with, I decided to try a load that seems to work great for other handloaders: 123 – 130 grain 6.5mm bullets with IMR 8208-XBR powder.

I started with Hornady 130 grain ELD-M 6.5mm bullets, because I’ve had great luck withthe ELD-M lineup:

Here’s the rest of the components:

Load specifics:

  1. Starline 6.5 Grendel cases (new)
  2. Hornady 130 grain ELD-M 6.5mm bullet
  3. 25.8 grains IMR 8208-XBR powder
  4. Federal 205 Primer
  5. 2.245″ COL

Use load data at your own risk. Ultimate Reloader is not responsible for errors in load data on this website. Always cross-reference load data with manufacturer’s published data.

100 Yard Range Results

At 100 Yards, I tested the CMMG Resolute in 6.5 Grendel with two different buttstock configurations, with the Ripstock, and with a Magpul MOE fixed buttstock. While the MOE was easier to use, I shot my best group with the Ripstock! Here are the groups:

5 Shots at 100 Yards, Magpul MOE

This is a great group for an AR, but things got better with Ripstock!

5 Shots at 100 Yards, CMMG Ripstock

I just goes to show what’s possible with this rifle (the borecam test was a foreshadowing) when you are focused on precision AR shooting techniques!

Close-Quarters Shooting

After shooting prone at 100 yards (and some 400 yard steel shooting) I decided to put this carbine into “carbine mode” with a SightMark reflex sight. This proved to be a lot of fun. I felt quite confident in hitting targets, and it totally changed the personality of this rifle. Recoil was noticeable (especially compared to a 223/5.56 AR-15) but quite manageable with the CMMG SV muzzle brake attached.

This is when I started to think about how versatile the CMMG Resolute in 6.5 Grendel is…

An All-Rounder AR

This CMMG Resolute Mid-Size AR in 6.5 Grendel has turned out to be surprisingly versatile. Here are some uses I see for this rifle in my own personal scenarios:

Target Shooting

Everything from close-quarters shooting to 100, 300, 600, even 800 yards.


Deer hunting, coyote hunting, rock chuck hunting, and perhaps even black bear hunting. More compact than other long-range capable ARs I own.

Home Defense

This would make a great rifle for home defense after determining the appropriate load, and perhaps with a reflex sight mounted.

A “Truck Gun”

With Ripstock, this rifle can be quite compact, and with a bipod attached, I could envision a versatile truck gun for defense and protection from animals (Ex: cougar that live in my hills).

For each of these scenarios there may be a better rifle in my safe (Example: 1000 yards shooting) but there aren’t too many ARs our there with the versatility that this rifle offers. That’s why I would reccomend this specific rifle as a great “all rounder”.

I consider this the “start of my journey” with this rifle- I’ll have more stories where I feature this rifle shooting/loading 6.5 Grendel, and comparing it to my Uintah Precision 6.5 Grendel upper (more on that shortly). I’m off to go shooting!

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5 thoughts on “TESTED: CMMG Resolute 6.5 Grendel Mid-Size AR with PowerBolt”

  1. Can you just change the bolt and use the regular ar 15 bolt carrier. I don’t want to buy another whole rifle.

    1. No,it will not fit. The bolt face is too wide and the bolt too long (look at the picture: far longer than the AR-15 bolt}. I agree with you: I am not paying to $1k plus for a one-off, one-caliber platform. I will run 6.5 Grendel in an AR-15 for a lot less cost with similar performance thanks.

  2. Gavin, this is why i watch your videos, you leave nothing to wonder about the product you are showing us. That looks like a really nice weapon and it was presented very well. Even when you take the weapon down and show us what you find and changes you can make to make it even better.
    Thanks Gavin.

  3. I had wondered many times why no one had ever manufactured a new sized bolt for the Grendel instead of milling out the 5.56 bolt face, making it too thin.

    My question: has CMMG or anyone else solved the magazine and mag well C.O.A.L. (2.34” absolute max, currently) for this fine cartridge?

    SO MUCH MORE PERFORMANCE is left on the table, because the ideal bullets have to be seated too deeply.

    It would seem that the Mutant mid size receiver is begging for a longer magazine, allowing a COL of 2.5” or so. This would accommodate the PPC’s, BR, Tubbs cartridges, and more.

  4. CMMG said the 6.5 grendel upper will fit on the MK47(7.62×39) lower.
    Grendels fit fine in AK mags.

    Any reasons this wouldn’t work? CMMG said it will not function but I can’t see why. Maybe the feeding angle? Any ideas?

    Thanks in advance!

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