by Tom Gaylord
Writing as B.B. Pelletier

Virtus AGE right
SigAir ProForce MCX Virtus AEG right side.

This report covers:

  • Spring piston
  • Battery basics
  • Avalon gearbox
  • Replacement M110 spring
  • This gun
  • Sights
  • Magazine
  • Velocity
  • Hop Up?
  • At what price?
  • Discussion
  • Summary

I did a search in the blog archives and could not find another report I had written about automatic electric airsoft guns (AEG). I have done some large articles about AEG in the past for Shotgun News and for my own newsletter. I even wrote two articles for Pyramyd Air about the basics of batteries for airsoft guns — one in 2008 and the other in 2009. Those articles are still good today — 10 and 11 years later.

Spring piston

An AEG is a spring-piston gun whose piston is retracted (cocked) and loosed by a mechanical gearbox that’s powered by a small high-torque electric motor. To power the motor a battery is contained somewhere inside the gun. There is a great animation of how an AEG works on Wiki.

Battery basics

Two things to know about AEG batteries — their milliampere-hour (mAh) rating and their voltage. The higher the milliamp-hours, the longer the battery lasts, which equates to the number of shots the gun gives on a charge. The higher the voltage, the faster the electric motor spins, which equates to rounds per second, because the principal reason for the existence of an AEG is to give full-auto capability.

The gun I am testing has a stick-type lithium polymer (lipo) battery that’s rated at 1100 mAh, which is on the low end, and 11.1Volts, which is quite high. That means a fast-firing gun that will need a recharge sooner than one that has a battery with a higher mAh rating.

Virtus AEG battery
The Virtus stick battery goes in the forearm. The yellow connector connects to the gun’s motor. The white connector is for the charger. The battery must be installed and removed again for every charge.

Stick-type batteries are designed to fit inside tight spaces within forearms. Sometimes there is enough room to stuff in an aftermarket battery with a higher mAh rating for longer operation. Sig says this 11.1V battery is the maximum allowable, but that refers to the volts, only. They don’t address the mAh. I will look into that for you. The thing you don’t want to do is use a battery with a significantly higher voltage, because the gearbox may not take the additional strain of faster operation. The thing is — this battery is already running close to the top in voltage, so you aren’t likely to do that. And then there is the gearbox.

Avalon gearbox

The MCX Virtus AEG has an Avalon gearbox with upgraded steel bearings. The gears are metal as well. I have built up airsoft gearboxes this way in the past, exchanging metal gears for plastic or Nylon, but this one comes to you ready to go.

Replacement M110 spring

The gun comes with an M120 mainspring installed and a replacement M110 spring to swap in if you like. The M110 spring will give a lower velocity (30 to 60 f.p.s. slower for a given weight BB) but put less strain on the motor and less drain on the battery. If you are doing a drill inside close quarters, the 110 spring is the one to have. It will give you longer operating time. If you are outside the M120 is the way to go. Sig has made swapping this spring very easy, and I will test the gun with both springs. I believe at this point that the M110 spring will allow the motor to run cooler longer in the full auto mode. We will see as we go.

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This gun

All right, I’m going to stop the tech discussion right there. There is a lot more to tell you, but now I want to shift your attention to the gun I am testing. The MCX Virtus AEG is a close replica of Sig’s MCX Virtus SBR firearm — their short-barreled rifle version of the Virtus. The airsoft gun’s receiver is CNC-machined metal and has M-LOK-compatible slots for accessories in the metal handguard. The metal stock telescopes to three positions and locks solidly in all three. It removes quickly to change the mainspring for power changes.

The gun weighs 6 lbs. 9 oz with a battery and an empty magazine. The length runs from 25-3/4- to 29-inches overall.

This is a select-fire airsoft gun with an ambidextrous thumb switch for Safe, Semi and Full Auto. If you are used to the M16/M4/AR-15, the switch is exactly where you expect it to be and the selection works exactly the same way. 

Sights

The MCX Virtus comes without sights. On a gun like this they would be back-up iron sights (BUIS). I will mount a dot sight for testing and, since Sig sent me the Romeo5 XDR, that’s the one I will mount. The gun has a M1913 Picatinny rail that runs 16 inches along the top of the receiver and handguard to augment the M-LOK slots on both sides and the bottom of the forearm. Mounting optics and accessories should prove no problem. Before you go crazy, though, remember that this is a close-quarters battle gun. Sights, a laser and a light are about all you want. Yes, thermal imaging, a rangerfinder and a bipod are nice options, but not when you are clearing rooms!

Magazine

The gun has a 120-round magazine that fits into the receiver just like an AR mag would. The release is in the same place and works the same so, once again, those who are familiar with the Armalite platform will be at home with the MCX Virtus.

Virtus AEG mag speedloader
Virtus magazine above and speedloader below.

Sig gives you a speedloader to fill the mag. The gun is rated for 0.20-gram BBs, and, as I have with other guns, I will test it with different BBs and different weights.

Battery box

Like most stick batteries in full-auto AEGs, the battery on the Virtus lives inside the forearm. Unlike many AEGs, the Virtus forearm slides off easily with the removal of a single captive pin. I have fought M4 handguard keepers for days, trying to install and remove batteries! There seems to be plenty of room inside the forearm of this one for larger batteries, but I have asked Sig if a higher mAh rated battery is acceptable, since they do not want you to use one with higher voltage. I understand the operational difference between volts and amperage, but I still want to hear from them.

Velocity

As it comes Sig rates the gun at up to 370 f.p.s. That would be with the M120 spring installed and using a 0.20-gram BB. Naturally I will test that with a lot of ammo, and then install the M110 spring and test it, as well. It looks like I have a lot of testing ahead of me!

Hop Up?

An airsoft gun in this price range has to have Hop Up. This one is mounted on the steel bolt. Dial the toothed wheel up or down to adjust the backspin on the BB.

And this answers another question — does the dust cover really work? Yes, it does — just like the firearm. The forward assist, however, is just for show. It is spring-loaded but is cosmetic, only. I still remember tap, tap, pull, tap as the mnemonic for a jammed M16 — because in my day they always did.

Virtus AEG receiver
The dust cover is up. At the left you can see the spring-loaded forward assist.

Virtus AEG Hop-Up
Retract the bolt to see the Hop-Up adjustment (arrow).

At what price?

On the Sig website they have the MCX Virtus AEG in stock at the full retail of $459.99. All the dealers I checked with who list them minus the battery and charger for $399.99 were sold out. Hmmm — might there be an axiom there?

Discussion

This is not a kid’s toy AEG. This one is serious, and Sig intended it to be. It’s heavy, solid and cold to the touch. The rest of what it is will have to wait for the next report.

Summary

We are starting to test a real high-end AEG here. This test will be thorough and long, for there is a lot to look at!