The Biggest AR Ever: NEMO OMEN .458 Winchester Magnum

It is no secret I like big-bore rifles. I also like ARs. So far, these two obsessions have been rather mutually exclusive. In an attempt to eke more horsepower out of the AR platform, I was an early adopter of the 6.8 SPC, .458 SOCOM, and the .338 Federal in my Elmer Keith-like obsession for a powerful AR. And while all of these calibers have their niches, I always lusted for more. Enter NEMO.

Known for precision, military-tough arms, NEMO rocked the shooting world two years ago by introducing the TiONE (an all titanium one-off AR designed to showcase their manufacturing capabilities) followed by a magnum-sized AR action large enough to handle the .300 Win. Mag. They fittingly named it the OMEN.

After seeing this extra-large action, my wheels began to turn. So when I met Clint Walker, NEMO's cofounder, I posed the question that had been bouncing around my cluttered brain: "Why not use an OMEN action to build a .458 Win. Mag.?"

Unlike my fantasy approach to firearm manufacturing, NEMO bases its product development decisions on a rifle's usefulness for military operators.

Clint's simple and very valid response was, "Why?"

"Why? Why not? Who wouldn't want a 10-shot semiauto .458 Win. Mag?" I asked. "Hell, man, every red-blooded Texan would buy at least two — one for his pickup and one for his wife's SUV."

I joked, but at the same time was more than half serious. If I wanted one, there had to be some other crazy rednecks who would feel the same.

In all seriousness, a .458 Win. Mag. AR would have some serious advantages in the hunting world. The NEMO offers a capacity of more than twice its nearest bolt-action competitor, piston-driven reliability, reduced gas-operated recoil, and durability that could stand up to the harshest hunting conditions.

Bear, moose, and nilgai hunters would swoon. Alaskan guides who want the ultimate brown bear backup rifle would welcome the offering. While unconventional for an African safari, I can't think of a more effective Cape buffalo rifle, though getting a semiauto into most African countries can run the gamut from problematic to impossible.

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After thinking it over, Walker put me in touch with Josh Sonju, NEMO's cofounder and vice president of research and development.

"Yes, I think we could do that," he said. "I hunt with ARs all the time and built an OMEN in .338 Win. Mag., so a .458 Win. Mag. shouldn't be a problem."

Several months later, I received the gun. I would like to say it's a one-off, but Josh was bitten by the big-bore bug (I knew there were other like-minded rednecks out there) and built a second for himself.

The Specs

Tipping the scales at 12.4 pounds, this is no small rifle. Then again, when shot-putting 500-grain slugs downrange at 2,090 fps, I am not a fan of light rifles anyway. More importantly, this rifle balances well. Even with a magazine loaded with 10 rounds of Federal 500- grain Fusion and an Aimpoint PRO atop for a total combined weight of 14.5 pounds, it still balances comfortably and directly in the hands.

The 18.5-inch 416 stainless barrel with its black Cerakote is impervious to harsh conditions. The upper and lower receivers are both hard anodized tan with black accents.

Shooting The Beast

The rifle was even more impressive on the range. Most onlookers said, "I bet this will knock your fillings out," but most of those guys have never shot a true big-bore rifle. I have shot a ton of .458 ammo through a lot of different rifles, and this one is easily the most comfortable. There are three main reasons: the large brake on the muzzle, the gas system, and the physical weight.

Conclusion

Overall, the NEMO was no surprise in the construction department. I have shot several NEMO rifles in the past, and all of them have been consistently well made. The caliber itself was a surprise. Getting a straight-walled case with pretty blunt bullets to feed in a semiauto is no easy task, but Josh modified their standard magazine followers and got it to work well.

In our tests, we had minimal failure, with both Federal Fusions and Federal Premium Hydro Solids. With a little breaking in, load experimentation, and fine tuning the gas system, I believe this rifle would be as reliable as most other dangerous game offerings.

What's next? The doors are literally wide open for NEMO and hunting ARs. Obviously, the long-range big-game crowd is covered with NEMO's flagship .300 Win. Mag. Creating a .338 Win. Mag. is no problem, and as we have just discovered, the biggest of the Winchester Magnum family is also within the realm of possibility.

While .375 H&H is out due to its overall length, at first glance it appears that the .375 Ruger and .416 Ruger would fit inside a NEMO magazine and work within the pressure parameters just fine. Josh seems to agree, so who knows, there may be another big-game NEMO offering just over the horizon.