NEMO Omen .300 Win. Mag. Review by Guns & Ammo

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by Tom Beckstrand | August 19, 2013

Few shooters will argue that the most relevant contemporary small arm is the AR-pattern rifle.

It is a wildly popular rifle that, up until recently, was readily available in everything from .22 Long Rifle to 7.62 NATO. The AR can attribute its success to its simple modular design, easy maintenance and comfortable ergonomics. The military is so enamored with it that they field numerous versions chambered in both 5.56mm and 7.62mm.

The 7.62x51mm rifles that our military uses are sniper rifles employed across both the conventional and special operations branches. The current-issued M110 weighs 10.44 pounds—that’s empty, without optics or any ancillary equipment. It has a 20-round detachable box magazine that feeds 175-grain Sierra MatchKing bullets into the chamber. They leave the muzzle at around 2,575 feet per second and, depending on which branch of service you talk to, are effective out to 800 meters (according to the U.S. Army Special Forces) or 1,000 yards (according to the Marine Corps).

If we desire more ballistic horsepower than the 7.62x51mm cartridge offers, we’re forced to abandon the semi-auto AR and grab a bolt gun. I love bolt-action rifles and appreciate the many comforts they offer, but they will always be slower-shooting rifles when compared with semi-autos. Slow is a problem for a sniper or for anyone who wants to cut down his reengagement times shot-to-shot. So if you wanted the performance of a .300 Win. Mag., you had to shoot a bolt-action rifle and just realize that time wasn’t going to be on your side. That is, until NEMO’s Omen showed up.

Collapsing Carriers
Chambering the AR in .300 Winchester Magnum brings a whole new capability to long-range shooters. It allows long-distance shooters to deliver multiple shots without having to break our position to cycle a bolt. An entire generation of riflemen has grown up with the AR and is intimately familiar with its handling characteristics. Magazine changes are quick and easy. The modularity of the design lets the user tailor the rifle to exactly what he wants and draw from several options that already exist on the commercial market. For military and LE snipers, no rifle is more night vision friendly than an AR. Last, but not least, we get the superb external and terminal ballistics of the .300 Win. Mag., a cartridge much superior to the 7.62 NATO for long-range work.

A friend of mine in the gun business once told me that building an AR chambered in 5.56mm is fall-off-a-log easy. Building one in 7.62mm was infinitely more complicated and much more difficult to actually accomplish. When I spoke with Clint Walker, NEMO’s vice president, he agreed with that statement. When I asked him if building an AR in .300 Win. Mag. was an order of magnitude more difficult than a 7.62mm, he quickly agreed.

Direct-impingement rifles have a very simple operating system. Gas from burning powder gets channeled through a port in the barrel, down a gas tube and into the upper receiver, where it pushes the bolt carrier group away from the chamber, extracting the recently fired case. As the bolt carrier group comes forward, it strips a round out of the magazine and pushes it into the chamber. This isn’t a complicated operation.

The trouble starts when we increase the size and power of the cartridge. More powerful cartridges require beefier bolts to handle the abuse the cartridge dishes out and heavier bolt carriers to manage the velocity at which the bolt carrier group travels rearward. If the bolt carrier group moves too fast, extractors cannot hold on to the case when they try to pull it from the chamber. The larger cases have more surface area and require more force to pull them out. Try to do it too quickly, and the extractor will pull right through the case rim, leaving the case stuck in the chamber.

Upon receiving the Omen, I immediately fieldstripped it to examine each component thoroughly. I noticed that the bolt carrier had a spring-loaded extension that rode in the rear of the carrier. Clint explained to me that the bolt carrier extension was a crucial part of NEMO’s recoil-reduction system. The extension allows NEMO to use a standard 7.62 lower receiver extension (buffer tube) for its .300 Win. Mag. rifle, becoming one less wheel NEMO had to reinvent.

Upon firing a cartridge, the bolt carrier group travels down the receiver extension until it makes contact with the end of the tube. The carrier extension then collapses into the bolt carrier until all rearward movement stops and the carrier group begins its journey back toward the chamber. Not only does the Omen have the AR’s standard buffer and buffer spring to help retard bolt carrier velocity at the beginning of the bolt’s cycle, it has the carrier extension further dampening recoil at the end of the bolt’s cycle. The system allows NEMO to use a large-enough bolt carrier to handle the .300 Win. Mag. pressures and still use a standard, readily available 7.62x51mm lower receiver extension. It’s a simple solution to what could have been a complicated problem.

Ports and Port Pressures
So NEMO cracked the code on the bolt carrier and lower receiver extension problem, only to be confronted with a new problem. The increased size and mass of the bolt and bolt carrier meant they needed more gas to make it move. As it stands right now, the Omen has a gas system that is approximately 14 inches long. The low-profile gas block sits just inside the forend, where it is well protected.

NEMO set the length of the rifle’s forend by mounting the longest scopes issued to our military on the Omen, then figuring out how much rail space they needed in front of these scopes to mount the most popular night vision and thermal devices. This way they had all the rail space they needed without carrying anything extra. This is an excellent approach when trying to minimize the weight of the rifle (as every manufacturer should).

It looks to me like Nemo then took the forend length they adopted and put the longest gas system they could stuff under it. Also smart methodology. The longer the gas system, the lower the gas pressure at the port. Lower port pressures mean lower bolt velocity. This makes extraction easier and also prevents premature wear on bolt lugs, extractors and magazine feed lips.

The dilemma presented by the .300 Win. Mag. is that even with a 14-inch gas system, the port pressure is still high. Likewise, the heavy bolt carrier group requires a lot of gas to get it moving, so the port has to be big to allow enough gas to cycle the gun reliably.

A large gas port and high port pressure mean that the Omen extracts aggressively. The Omen comes with a gas port optimized for 150- to 190-grain bullets. I was shooting Hornady’s 150-grain GMX Superformance loads. If the Omen was going to have a malfunction, the combination of light bullets loaded to maximum velocity should have caused it. On the contrary, the Omen ate every round I fired with no malfunctions. I did notice that some of the fired cases showed ejector marks, and I could see where the extractor was trying to pull through the case rim but couldn’t. Once again, light bullets loaded to max velocity are the most problematic loads for an AR chambered in .300 Win. Mag. Hornady also has soft brass, so a few of the cases popped the primers out while firing. While the Omen was 100 percent reliable, it was hard on Hornady’s soft brass.

Premium Components
Being the first to produce an AR in .300 Win. Mag. meant that NEMO had to build their own upper and lower receivers, bolts, bolt carriers and barrel extensions. I weighed the Omen bolt and bolt carrier to compare them with their counterparts from an AR-15. I’ve included a table that compares their weights.

.300 Win. Mag. 5.56 NATO
Bolt 2.6 ounces 1.5 ounces
Bolt Carrier 15.2 ounces 9.5 ounces

There is a noticeable difference in both size and weight between the Omen components and the traditional AR-15, as you would expect when comparing a .300 Win. Mag. with a 5.56.

A component of any AR-pattern rifle that bears special scrutiny is the bolt. The bolt has eight small lugs that pass into and out of the barrel extension with each firing. The lugs on either side of the extractor are only attached to the bolt on one side, and, when AR bolts fail, one of these two lugs is usually the culprit.

Back in 1957, Eugene Stoner chose a blend of steel known as Carpenter 158 as “the standard” material from which AR bolts would be made. Only Carpenter Steel, based in Pennsylvania, makes the steel. It is excellent steel, but there is nothing magical about its properties. Once Eugene Stoner chose Carpenter 158 as Mil-Spec, some decided that it was as if God himself declared it superior to any other material. This is not the case.

Carpenter 158 comes from a family of tool steels. Also in this family are 8620 and 9310. Because Carpenter 158 is only available from one source, the manufacturer will only sell it in very large quantities, making it difficult for smaller AR manufacturers to acquire. Most smaller manufacturers will buy the cheaper 8620, which really isn’t as good as 158. However, I think the more expensive 9310 is a better bolt material than Carpenter 158. It has a higher nickel content and is less brittle than 158. For a part that has eight small lugs that slam into the barrel extension and rotate into and out of battery every time we fire the rifle, less brittle seems like a wonderful idea.

NEMO, in their quest to bring a premium product to the market, chose to make their bolts out of 9310. They also thought it prudent to coat both the bolt and bolt carrier in nickel boron. This is an excellent choice and not a cheap one. Not only is NEMO willing to be the first to manufacture an AR in .300 Win. Mag., they choose to use only the best materials and coatings while doing so.

Experiencing the Omen
My time on the range with the rifle was considerably more pleasant than I imagined. When I received the rifle, I took it out of the case and noticed that it had a flash hider and not a muzzlebrake. I thought it a mistake not to put a muzzlebrake on a 10½-pound semi-auto .300 Win. Mag. and figured I would be paying for NEMO’s choice in the very near future.

I quickly learned that the rifle is incredibly soft-shooting, caliber notwithstanding. The stock that came on the rifle wasn’t the most comfortable (it’s easily changed out for whatever the shooter prefers), and the rifle was still pleasant for the duration of the range session.

The Omen’s accuracy was also better than I initially imagined. I saw the lightly contoured fluted barrel and thought it would have a tough time maintaining tight groups as the session wore on. The .300 Win. Mag. generates a lot of heat that murders skinny barrels. Shooting Hornady’s 150-grain GMX loads, my best five-shot group at 100 yards measured .88 inch center-to-center. The largest group was 1.4 inches, and the average was 1.2.

My range session was a bit unfair for the Omen, in that I didn’t stop for long to let the barrel cool even when it got really hot. However, I helped out the rifle by loading six rounds in the magazine for each group and fired the first shot into the backstop. That’s a little trick I learned from David Tubb. The first round chambers differently because it’s frequently loaded by releasing a bolt that’s been locked to the rear. When we fire, the rifle cycles and loads at a different bolt speed. The difference causes that first round to chamber slightly differently than the rest. Any difference, no matter how small, affects accuracy.

Overall, I’m excited to see what NEMO can accomplish with their Omen. I think it’s an excellent rifle made from quality materials. I don’t love the FAB Defense stock that came on the rifle, but it’s easily replaced. I’m also suspicious of the magazines NEMO has to manufacture. I’m not convinced they’ll handle abuse well. If you buy the Omen, get some spare mags.

The Omen is a great choice for anyone interested in long-range shooting. With the superior ballistics of the .300 Win. Mag. matched with the ergonomics of the AR, it makes for a rifle that’s fun to shoot for hours at a time. For hunters and tactical shooters alike, the Omen is an exciting development and one that I’ll watch closely.

NEMO Omen_300 Win Mag

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Look for the NEMO Omen in Book of the AR-15, a publication dedicated to all rifles, optics, and ammunition engineered for the AR-15 platform.
Order your copy at the InterMedia Outdoors Store today!

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