If you’ve been curious about the all-new 6mm ARC cartridge, you’re in the right place! I’ve been having a great time getting hands-on with this new cartridge: both with my own handloads, and with factory ammunition. In this article I’ll give you an in-depth look at CMMG’s new Endeavor 300-series AR-15 chambered in 6mm ARC!

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CMMG Has Everything You Need for 6mm ARC

CMMG has made a big investment in this new cartridge from Hornady, including rifles, barrels, uppers, and combo packs. Here’s a break-down of those 6mm ARC products!

CMMG Endeavor 20″ AR-15 Chambered in 6mm ARC (subject of this article)

From the CMMG Product Page:

CMMG’s ENDEAVOR line of rifles are now available in Hornady’s new 6mm ARC (Advanced Rifle Cartridge). Designed for superior long-range accuracy, the ENDEAVOR line features a 20-inch barrel so that you can squeeze out every drop of ballistic performance from this exciting new caliber. Each rifle ships with one 10-round magazine.

TECH SPECS:
CALIBER: 6mm ARC
BARREL: 20”, 1:7.5 twist, 6mm ARC, MT 416SS, SBN
MUZZLE: MUZZLE: SV Brake, threaded 5/8-24
GAS PORT LOCATION: Rifle Length with SLR Adjustable Gas Block
RECEIVER: Forged 7075-T6 AL M4 type upper, AR15 type lower
HAND GUARD: CMMG RML15 M-Lok hand guard
FINISH: Cerakote Receivers and Hand Guard
CHARGING HANDLE: CMMG Oversized Ambi
BUTT STOCK: Magpul PRS
TRIGGER: Geissele Automatics SSA 2-Stage
TRIGGER GUARD: Magpul MOE
SAFETY SELECTOR: CMMG Ambi
MAGAZINE: 10rd
WEIGHT: 9lbs 2oz(unloaded)
LENGTH: 40.5”

CMMG Resolute 16.1″ AR-15 Chambered in 6mm ARC

From the CMMG Product Page:

Meet CMMG’s newest long-range offering. Chambered in Hornady’s new 6mm ARC (Advanced Rifle Cartridge), the CMMG’s RESOLUTE line of rifles bring this exciting caliber to the proven AR15 system for superior function and performance. Each RESOLUTE rifle chambered in 6mm ARC features a medium tapered 16-inch barrel and ship with one 10-round magazine.

TECH SPECS:
CALIBER: 6mm ARC
BARREL: 16.1″, 1:7.5 twist, 6mm ARC, MT, 416SS, SBN
MUZZLE: SV Brake, threaded 5/8-24
GAS PORT LOCATION: Rifle Length with SLR Adjustable Gas Block
RECEIVER: Forged 7075-T6 AL M4 type upper, AR15 type lower
HAND GUARD: CMMG RML15 M-Lok hand guard
FINISH: Cerakote Receivers, Hand Guard, and RipStock
CHARGING HANDLE: CMMG Oversized Ambi
PISTOL GRIP: Magpul MOE
BUTT STOCK: CMMG RipStock with 6 Position FASTBACK Receiver Extension and Ambi Sling Plate
TRIGGER: Geissele Automatics SSA 2-Stage
TRIGGER GUARD: Magpul MOE
SAFETY SELECTOR: CMMG Ambi
MAGAZINE: 10rd
WEIGHT: 6lbs 7oz(unloaded)
LENGTH: 32.8” (stock collapsed)

CMMG 6mm ARC Uppers, Barrels, Magazines, Packs

If you already have a rifle, perhaps you’ll want a barrel, upper, magazines, or a combination thereof. If that’s the case, you can see all CMMG 6mm ARC parts, accessories, and uppers HERE.

CMMG Endeavor 300 6mm ARC: What’s In the Box

The 6mm ARC Endeavor 300 comes with the following:

• Complete rifle
• 10 round 6.5 Grendel / 6mm ARC magazine

Gavin’s 6mm ARC all Tricked Out

After unboxing the Endeavor 300, I added the following:

• Nikon BLACK FX-1000 6-24x50mm FFP scope
• Nikon Black cantilever mount
• KRG Full-length ARCA rail
• Mystic Precision MPOD F-Class style bipod with custom ARCA adapter
• SilencerCo Hybrid silencer
• TriggerTech Diamond AR two-stage trigger (upgraded from Geissele SSA AR-15 trigger see below)

And that’s an awesome AR package for the 6mm ARC!

Triggers: and TriggerTech Diamond AR

TriggerScan Results: Geissele SSA AR-15 trigger

This data was collected for my review of the CMMG Mid-size 6.5 Grendel rifle, for the complete story, please click here:

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

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! However, I do all of my accuracy testing with a TriggerTech AR Diamond, so I installed that trigger in the Endeavor.

AR Diamond Trigger Scan Results

My focus scenarios for testing the AR Diamond were MIN pull weight and MAX pull weight. Here’s the results from those tests:

This trigger is advertised as a 1.5lb to 4.0lb trigger, and I noticed that you can actually change the TriggerScan results (peak force) by moving the load cell (actuator) up and down on a flat bladed trigger. So if I were to move the actuator down on the trigger, I’d be really close to the 1.5lb –  4lb peak force adjustment range. Here’s a table summarizing the results:

If you look at all of the data together (including a 3-pass test I did at near-but-not-min pull weight for the AR Diamond) you can see visually how the AR Diamond stacks up against the Geissele Automatics trigger I’ve upgraded from:

For the testing with the CMMG Endeavor 300, I used the lightest trigger pull.

Overall Performance Summary

For a full summary of load development and accuracy testing, see the following article:

6mm ARC: Fact or Fiction? Real Performance Results, From-Scratch Experimental Load Development

Here are some excerpts from that article, all using the CMMG Endeavor 6mm ARC AR-15!

Test Load #1: Hornady  108 grain ELD-M and Hodgdon Varget

I chose to start with Varget because of what I read about 6mm PPC, and I have a lot on hand! Using QuickLoad, I worked up the following load:

HOT Experimental Load Data, Do NOT USE

• Bullet: Hornady 108 grain ELD-M 6mm
• Case: Hornady 6mm ARC (new and 1x fired tested)
• Powder: 27.0 grains Hodgdon Varget
• Primer: CCI BR-4 (for 1x reloads)
• COL: 2.260″

For this load, I shot a group of 5 shots on the chronograph, and observed the following:

• Velocity: 2602 FPS average
• SD: 7.6 FPS

This load produced very mild indications of pressure on the case rim, and functioned in the rifle well. It also produced the best accuracy as seen here:

This load is a good performer, but I wanted to see if I could get more velocity from the 108 grain ELD-M bullets, so I tried a different powder!

Test Load #2: Hornady  108 grain ELD-M and H-4895

H-4895 is closer to the “6.5 Grendel” sweet spot, so I thought it would be worth a try. Again using QuickLoad, I developed the following load:

HOT Experimental Load Data, Do NOT USE

• Bullet: Hornady 108 grain ELD-M 6mm
• Case: Hornady 6mm ARC (1x fired)
• Powder: 26.6 grains Hodgdon H-4895
• Primer: CCI BR-4
• COL: 2.260″

Here I saw velocities averaging 2,631 FPS. Accuracy was good, with one group I captured on camera (see video) measuring 0.750″:

Hornady Factory Ammunition Results

It took quite a while to get a hold of the Hornady factory 6mm ARC ammunition (everyone wants it!), and once I did get it, I tested for velocity data right away with my Magnetospeed V3 chronograph.

Velocity Data: Hornady 108 ELD-M Match Ammunition

The factory Hornady 108 grain ELD-M Match ammunition definitely had better velocity and pressure numbers compared to my handloads. This ammunition showed a gain of 30 fps from the CMMG Endeavor, with less pressure signs. I’m thinking it will be interesting to break down some cartridges to see what’s inside!

Here’s the interesting data point: using QuickLoad, I show that with 2,660 FPS and a 20″ barrel, if we were to increase the barrel length to 24″, the velocity that QuickLoad estimates would be EXACTLY 2,750 fps, with an AR-15, and that’s what Hornady has published for their performance claims. Very interesting- performance confirmed again!

Velocity Data: Hornady BLACK 105 grain Ammunition

The 105 grain Hornady Black ammunition have even more velocity- with an average of 2,678 fps for 5 shots, and a lower SD of 11.4 fps.

I did not perform in-depth accuracy testing with either type of ammunition, but group sizes were larger compared to my hand loads.

Conclusion

My CMMG 6mm ARC Endeavor 300 performed quite well, both from a velocity perspective and an accuracy perspective. With CMMG also stocking magazines, barrels, uppers, and combo packs, you should definitely check out what they have to offer if you are interested in shooting 6mm ARC! I’d like to know what you think of 6mm ARC, and this CMMG Endeavor 300- please leave a comment!

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Thanks,
Gavin