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SIG Sauer’s MCX Virtus offers new take on AR platform possibilities

Like SIG’s P320 handgun, the MCX Virtus Patrol rifle can be assembled into various configurations, sizes or barrel lengths based on operational or individual needs


Taking the modularity concept to the rifle world, SIG Sauer offers the MCX Virtus Patrol.

Photo/Andrew Butts

SIG Sauer has gone all in with the idea of firearms modularity and has had great success with the P320 modular handgun.

Using a central chassis as the serial-numbered frame, the P320 can be assembled into a full-size, compact or sub-compact pistol without the need for tools or armorer-level work. This affords a police department or individual police officer the ability to configure one pistol to meet multiple roles.

Taking the modularity concept to the rifle world, SIG Sauer is producing a rifle called the MCX Virtus Patrol.

MCX rifle assembles into various configurations

Like the P320 handgun, the MCX rifle can be assembled into various configurations, sizes or barrel lengths based on operational or individual needs using just the one serial-numbered lower receiver.

The MCX’s buttstock can be easily swapped out between a folding, folding/telescoping or sliding stock with nothing more than a Torx wrench. The barrel and hand guard can be just as easily changed.

The rifle can be switched from a 16-inch barreled 223 Remington with a folding stock to a short-barreled rifle (follow applicable laws) in 300 Blackout with a telescoping stock in mere minutes with no complicated tools or dedicated work area. All that’s needed are the parts and some basic mechanical aptitude.

SIG offers several barrel, stock and hand guard options that allow the rifle to be assembled into any number of configurations. SIG is also planning to sell an MCX conversion kit that includes the complete upper and a stock assembly.

Those departments with inventories of used M16 rifles will be able to easily convert these old guns into a modern format given the fact that the MCX is designed to work on any standard AR lower.

Even though the MCX is based on the AR15, it does have some notable differences:

1. Piston operating system

Piston-operated rifles will generally run longer with less maintenance than their direction impingement cousins. This can especially be true when using a suppressor.

2. Adjustable gas system

The MCX’s gas system is adjustable and can be somewhat tailored to the ammunition or suppressor being used. This can be quite beneficial when shooting 300 AAC Blackout because this cartridge can be somewhat anemic in subsonic loadings. These light loads can negatively impact reliability with their reduced operating pressures, often requiring a larger gas port over what works well for supersonic ammo.

3. Relocation of rifle’s operating springs

Another benefit to the MCX is the relocation of the rifle’s operating springs. Gone is the tubular receiver extension and large action spring found on a traditional AR. Instead, the MCX runs with two small springs that are located alongside and above the bolt carrier. With the relocation of the action springs, the rifle can be outfitted with a folding stock for easier transport or storage.

The MCX is going to be immediately comfortable to anyone accustomed to an AR15. The design parameters are such that the rifle handles and feels familiar and should take little additional practice or training.

Shooting the MCX

On the range the MCX offered no surprises. By this I mean the rifle met my expectations. It was reliable and accurate and I had no issues whatsoever over the course of several day’s use.

I used a variety of 223 Remington ammunition including expensive “match grade” ammo, inexpensive steel-cased blasting ammo and commercial remanufactured fodder with no problems. This held true when switching barrels and running the rifle as a 300 Blackout with and without a suppressor.

All in all, the MCX Virtus is a new and interesting take on what’s possible with the AR platform. SIG has done an admirable job of tweaking an existing design and pushing it probably about as far as it can go while still maintaining the familiarity of the firearm on which it is based. So when does a rifle based on the AR15 stop being an AR and become something new and different? I think SIG Sauer has answered that.

SIG Sauer MCX Virtus Patrol Specs

Caliber: 223 Remington (also available in 300BLK)
Action Type: semi-auto
Barrel: 16” cold hammer forged 1X7 twist
Overall length: 35.5” with stock open 26.5” with stock closed
Receivers: aluminum alloy, stealth gray finish (FDE also available)
Operation: short stroke gas piston, 2 position
Weight: 7.9 pounds empty
MSRP: $2,233.00

Andrew Butts has served as a soldier in the Army National Guard and also served as a correctional officer in Montana, and is currently with a federal law enforcement agency. Butts currently holds an Expert classification in IDPA and an A classification in USPSA in both Limited and Single Stack Divisions.

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