Odin Works 21″ 6mm ARC Complete Upper: Reviewed

When 6 ARC was announced by Hornady, I was among the many that were extremely excited and chomping at the bit to test it out for myself. My options for getting an AR15 in 6 ARC were to build one for myself with scavenged components, to buy a complete rifle, or to get a completed upper. Scrapping one together on my own comes with challenges I wasn’t looking forward to, and buying a complete rifle required a wallet that was thicker than mine. Luckily, Odin Works quickly whipped up an 18″ and a 21″ barreled completed upper option! I promptly invested in their 21″ offering because of the great experience and results I’ve had with their products in the past. Yes, that’s right, I bought this with real money.

I spent many different days at the range across a few different states with my Odin Works 6 ARC upper. Here, I’m shooting steel between 350 and 780 yards using my PhoneSkope adapter to video through my Meopta Meostar S2 spotting scope.

Build Details

The options that I went with for my complete upper are as follows: 15.5″ O2 Lite handguard, billet upper receiver, 21″ barrel with Odin’s XL Rifle gas system. The next thing I knew, the completed upper arrived at my doorstep and I had a completed rifle after I snapped the upper on my waiting lower receiver. The lower I used features a Magpul PRS Gen 3 stock, Ergo Tactical Delux vertical grip, and Timney Daniel Horner Signature 2-stage Trigger. I then topped the upper with a Leupold Mark 5HD 3.6-18×44 sitting securely in a Leupold Mark AR 35mm ring offset mount. Because the barrel is threaded 5/8×24, I also had the option of installing a suppressor on this build. During my testing, I used an AAC Jaeger 30 periodically to keep things quiet.

At this point, I sat back to admire my new masterpiece. The whole build looked sharp, but looks weren’t everything! After cleaning the barrel to remove any kind of leftover debris from the manufacturing process that most new firearms have, I took the first available opportunity to run to the range. We’ll discuss what I saw at the range in a bit, but for now, let’s talk about what I thought about the upper itself:

Odin Works’ billet upper does not feature a forward assist, but I never needed one. The O2 Lite handguard is not only functional and light but very attractive looking.

Thoughts After Range Day

As expected of Odin, I enjoyed each and every aspect of their completed upper. Thanks to the M-LOK system on the O2 Lite handguard, I was able to mount a Magpul bipod directly to it. As with any M-Lok attachment, this was a solid interface that was also very easy to use. With the Handguard being 15.5″ long, I was also able to get the bipod out pretty far to increase my stability. With the XL rifle (2″ longer than rifle) gas system, the adjustable gas block barely sticks out past the handguard. This leaves the adjustable screw exposed and very easy to adjust. This screw has a spring-loaded detent that keeps it in position without a locking screw. It also clicks when you turn the screw, giving you a convenient way to reliably change the gas system from suppressed to unsuppressed, and back.

The barrel is 21″ long with a threaded 5/8×24 TPI muzzle and 0.875″ gas block diameter. It’s constructed of 416R stainless steel with a 1:7.5 twist and comes in at a hefty 3 pounds and 9 ounces. All Odin Works barrels are hand lapped and button rifled for that extra durability and ultimate accuracy.

The adjustable gas block just barely peeks out under my 15.5″ handguard, allowing easy access for gas adjustments on the gas metering screw out front.

The billet upper receiver itself lacks a forward assist and has a fairly low-profile deflector that worked plenty well. The bolt that comes with this upper is a 6.5 grendel bolt face but the BCG is pretty much a standard full Auto BCG. The BCG lacks any kind of lightning cuts and is double vented for gas to escape through the ejection port.

Over the course of several range-day sessions, I fired several hundred rounds through my 6 ARC. I did this before writing a review for a couple of reasons: First, I want to provide a detailed, adequate review. Second, I kept hoping to see 1 hole groups at 100 yards, but I wasn’t quite. Third, I needed to know if anything would change after that “wear in” period, whether it be functionality, accuracy, or reliability.

The included BCG isn’t anything out of the ordinary, other than it features a 6.5 grendel sized bolt face to accommodate the 6 ARC.

Discussion on Accuracy

As with all new calibers, I always hope that the current one is the holy grail of ultimate accuracy and ballistics. Unfortunately, they never prove to be “the one.” My first range day consisted of firing several boxes of Hornady ammunition at range, and at the 100-yard berm. I used Hornady 108 grain ELD-M, 103 grain Hornady ELD-X and 105 grain BTHP Hornady Black ammunition. Velocities from this 21″ barrel were recorded as 2654 FPS, 2687 FPS, and 2688 FPS respectively. From day one, group one, my rifle shot the ELD-M offering best(ish)… picture below.

As you can see, the first 9 shots out of my Odin Works complete upper in 6 ARC shot about MOA. This is only a 3 shot group example because I was not considering this the final accuracy test.

These were 3 shot groups because I was not ready to call these official accuracy tests. At the time, my rifle had 9 rounds down the barrel and those are the ones you see on paper, with the flyer on the ELD-M group being the first round ever fired (what luck with the bore-sighting). After continuing to shoot this gun, I noticed a trend that made me sorta sad… 5 round groups would result in 2 separate, and small clusters of shots, with every other shot landing in the opposite cluster (check photo below to see what I’m referencing).

I lightly circled each individual group with a pencil for your reference. Below each group, you can see the group size listed in inches as well as MOA. If you look closely, you can also look at the holes in the target to find the shot number in the center in green.

I decided to give it the universal cure of time and diligence. This changed nothing. 250 rounds later, I get identical groups to what you see above. That said, as oddly shaped as it is, sub-MOA groups (with ELD-M) is good on any semi-auto platform, and I was able to get dependable performance at range. The day I wrote this review, I was absolutely pounding a 10″ circle at 770 yards, dropping 0 hits out of 20 shots taken. I even managed to fire a string of 3 off before hearing the steel report the first shot. This can be verified, of course, by all of my followers on social media since they enjoyed a short video of the event. In the end, I’m happy with this performance and I suspect that I could get even better results from this platform by handloading my own ammunition.

After doing some research to find out if anybody else experienced this type of accuracy with their 6 ARC, I stumbled across some youtube videos by Eagle Eye Shooting. He noted the exact thing that I was seeing with my 6 ARC. I recall him debating on it being an issue of bullet jump, possibly impacted by the magazine length restriction or violent nature of a semi-auto platform possibly seating the bullet deeper as it was chambered… I can’t quote exactly. If you want to know more, I urge you to find his videos because he seemed to have a wealth of knowledge on the 6 ARC specifically.

On the day of writing this review, I shot several hundred rounds in heat upward of 90 degrees. The barrel was too hot to touch most of the time and I still saw consistent performance.


  • Upper
    • 15.5″ O2 Lite M-Lok handguard
    • Odin Works Billet Upper Receiver
    • 6.5 grendel/6 ARC Type II BCG
  • Barrel
    • 21″
    • 416R stainless steel
    • XL rifle gas system
    • 0.875″ adjustable gas block
    • 5/8×24 threaded muzzle
    • 1:7.5 twist button rifled, hand lapped barrel
    • 3 pounds, 9 ounces
  • MSRP: $949.00

Final Thoughts

At first, I was disturbed by the groups that I was seeing with factory Hornady ammo. But after much research, and the finding of many reports of the same phenomenon with many different manufacturer’s products, paired with the fact that I can still observe sub MOA groups with the right ammo, I feel much better about this product. I’m convinced that this weird pairing of bullets within a group is not an Odin Works issue but is rather a 6 ARC issue. I also found the 6 ARC to be an EXTREMELY sooty round. I cleaned my barrel at one point to see if the accuracy would change, and I felt like I was sweeping a chimney. This isn’t a big issue other than it tended to gum up and gather on the BCG, in the trigger group, at the adjustable gas block screw, etc… It never impacted the performance that I observed but it was annoying nonetheless. Kudus to the Odin Works products chugging through the sludge and continuing to function properly.

Would I buy this product again? Certainly. I will definitely be buying Odin Works products in the future. If I got a redo, I would probably even buy this exact setup in 6 ARC again. As mentioned before, It’s hard to shake a stick at sub MOA performance out of a gas gun with ballistics as impressive as this moderately slow 6mm has to offer. It’s definitely a superior build to an AR10 chambered in 308, and perhaps 6.5 Creedmoor for most scenarios. As a whole, this gun weighs much less than an AR10 and it’s proved much more reliable than one of those behemoths. It’s a fact that AR10s are less reliable than an AR15 and you can’t convince me otherwise. But, I digress… this is apples to oranges in some ways. I hope this review helps you out in your never-ending search for that perfect rifle system/caliber combo.

Check out the Odin Works 6 ARC complete upper HERE!

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More Pictures:

This shows the hammer of the Daniel Horner Signature 2-stage Timney Trigger after being wiped down after use. Some stubborn soot still remained.
The charging handle is not ambidextrous, but it does have a large surface area for easy and comfortable manipulation.
The Leupold Mark 5HD I chose was a perfect match for this high-performance cartridge/system.
Even the “ugly” side of this AR15 was attractive.

About the author: Riley Baxter is an avid and experienced hunter, shooter, outdoorsman, and he’s worked in the backcountry guiding for an outfitter. He also get’s a lot of enjoyment out of building or customizing his firearms and equipment. Check out Riley’s Instagram @Shooter300

{ 5 comments… add one }
  • Ben October 12, 2021, 5:05 pm

    Check for any slop between the receivers!
    I built a 6mm Arc with a ER Shaw 22 inch barrel. I fired 6, 3 shot groups at 100 yards today that averaged .91 MOA (including pulls). I have a accuwedge at the back of the receiver and a #7 oring at the front. I’m using handloads 5 tho off the lands with Starline 6.5 Grendel brass, 27.5 gr of leverevolution and Hornady 105 bthp’s. Hope this helps.

  • Josh October 9, 2021, 4:41 pm

    I’m looking to build one jut like yours. It will be my first AR. I have been reading a lot about the 6mm arc and it’s the one I have chosen. What lower receiver did you use. Thanks for the review, very helpful.

  • Troy October 9, 2021, 3:55 pm

    I see no advantage of this to the Grendel
    With any factory loads 120-123 grain Federal and Hornady my 16” stainless light fluted barrel and a 8x Chevron will shoot .75” 5 shot groups and damn near 1” with steel Wolf
    That setup with 21” heavy bbl and the optic used should shoot lights out
    That round reminds me of the .224 Valkyrie same issues factory ammo averaged 1.5 MOA at 100
    Every article I read on that caliber they all shot over 1” with 20” bbls

  • QSYB October 4, 2021, 1:01 pm

    I’ll bet $100 it’s the pressure from the top round in the mag, that’s why the shots switch groups back and forth. The offset round is pushing the bolt left-right-left-right. Single-load them and see what happens.

    • Riley Baxter October 4, 2021, 7:05 pm

      That’s a good thought and it’s definitely worth testing! I’ll update this article with the results if anything comes of it.

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