Nemo Omen: 300 Win Mag AR (Yes, Really) By: Kat Ainsworth


If you’re a fan of semi-automatic rifles, odds are you’ve gone looking for larger caliber models. But the bigger the caliber, the less likely you are to find a big-bore semi-auto. Bolts are far more commonplace. Nemo Arms is changing that up with their OMEN Watchman, a 300 Winchester Magnum semi-auto capable of impressive precision. A 1 MOA AR platform rifle in 300 Win Mag? Yes, please.

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the OMEN Watchman 300 Win Mag semi-auto platform
According to the manufacturer, the OMEN Watchman is the world’s first viable, reliable, and accurate 300 Win Mag semi-auto platform. (Photo credit: Nemo Arms)

Nemo Arms provides details of the rifle:

The OMEN Watchman is the worlds first viable, reliable, and accurate 300 WM semi-auto platform. Built for ultra long-range applications, the Watchman makes precision shooting at extended ranges a breeze. At the Watchman’s core is a 24” Proof Research carbon fiber barrel, which is chambered in NEMO’s facility to ensure optimal accuracy performance. Extremely low recoil comes thanks to our own patented recoil reduction system which you won’t find anywhere else. This, combined with comfortable ergonomics gives the shooter confidence to shoot better than ever before. You must shoot it to believe it. The Watchman provides and exceptional shooting experience, allowing the shooter to perform at levels never before imagined.

Nemo Arms Omen rifle
The rifle has a NEMO upper and lower receiver set billet 7075-T6 that is hard anodized with tiger stripes. (Photo credit: Nemo Arms)

Features of the rifle include:

  • NEMO upper and lower receiver set billet 7076-T6 Hard Anodize tiger stripe
  • 15” 6061 M-LOK modular rail 1.83” internal diameter steel QD mounts rotation limited
  • Lightweight heat-dissipating barrel nut 7075-T6
  • 7075-T6 7 rifle length “Carrier Cradle” anti-tilt receiver extension Nickel Boron coated
  • Tuned steel-faced buffer system
  • Chrome silicon recoil spring
  • PROOF Research 24” Carbon fiber wrapped barrel 1:8 twist .300 win-mag chamber
  • NEMO dual chamber compact muzzle brake 6AL-4V titanium
  • 4-position adjustable gas system for suppressed and un-suppressed use
  • Severe duty threaded stainless gas tube extended length gas system
  • PATENTED recoil reduction carrier 8620 heat treated Nickel Boron coated
  • High-Pressure bolt 9310 heat-treated Cryo’d shot peened MPI Nickel Boron coated
  • Tool steel extractor heat treated IONBOND coated
  • Titanium through drilled takedown and pivot pins
  • Ambidextrous safety selector
  • Tool steel side charging handle Ionbond coated
  • Geissele Super semi-automatic enhanced (SSA-E) two-stage trigger First 2.3lbs Second 1.2lbs
  • MAGPUL MIAD grip
  • MAGPUL PRS adjustable rifle stock
  • NEMO 14-round magazine with aluminum follower
300 win mag rifle
The OMEN Watchman is designed specifically for long-range use. (Photo credit: Nemo Arms)


  • Caliber: 300 Win Mag
  • Barrel Length: 24 inches
  • Overall Length: 45.5 inches
  • Weight: 10.2 pounds, empty
  • Capacity: 10 rounds or 14 rounds depending on the magazine
  • Stock: Magpul PRS, adjustable
  • Pistol grip: Miad
  • Bolt: 9310 heat-treated Cryo’d shot peened MPI
  • Trigger: Geissele Super semi-automatic enhanced (SSA-E) two-stage trigger
  • Barrel: 24-inch Proof carbon fiber with a 1:8 twist rate
  • Handguard: 15-inch 6061 M-LOK modular rail
Nemo Omen Watchman rifle
The OMEN Watchman has a 24-inch Proof Research carbon fiber barrel. (Photo credit: Nemo Arms)

It’s nice to see a semi-auto in this caliber on the market, and Nemo has a solid reputation to back its quality and performance. Reports are this is a 1 MOA rifle as long as the shooter brings the skills to the shooting bench.

MSRP for the Nemo OMEN Watchman in 300 Win Mag is $6200.00.