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Education / Training SigAir ProForce MCX Virtus AEG airsoft gun: Part 2

SigAir ProForce MCX Virtus AEG airsoft gun: Part 2

by Tom Gaylord
Writing as B.B. Pelletier

Virtus AGE right
SigAir ProForce MCX Virtus AEG right side.

Part 1

This report covers:

  • My strategy
  • Sig BBs
  • Weight
  • Getting the gun ready to fire
  • Loading the magazine
  • Use the speedloader
  • The follower needs more BBs
  • Velocity 0.20-gram Sig BBs
  • Sound and feel of the shot
  • Rock and Roll
  • More about the speedloader
  • 0.25-gram BBs
  • Full auto accuracy
  • 0.30-gram BBs
  • Trigger pull
  • Summary

Today I start reporting on the velocity of the new SigAir ProForce MCX Virtus AEG airsoft gun. I say “start” because I can’t get the full report in a single day. You will recall that Sig enclosed a 110 mainspring for me to try, as well as the 120 that’s in the gun as it comes. The 110 spring is lighter, so two things should happen. The velocity should drop a little and the rounds per minute (RPM) should increase, because the electric motor is turning the gears against less force.

My strategy

I could either replace the spring and do the second velocity test next or I could go on to the accuracy test with this spring and then do the spring swap and test everything again. I think I will do the latter for a couple reasons. It’s easier, and I am into easier. And, even if I were to do anything wrong while making the spring swap, we will at least get one complete test.

My hope today is to get the velocity for some reasonable weight BBs, and also to sample the RPM. Let’s go!

Sig BBs

Sig provided me with a sample bag of 0.20-gram BBs with the gun. I have plenty of BBs in that weight, but I thought I would use theirs, since they were handy. They even loaded the speedloader — which made it more convenient.


I don’t know what brand BB Sig sent me. They don’t currently have an airsoft BB of their own, so I assume that these are a premium BB. But I weighed them to make certain. They weighed 0.20 grams on the nose except for one that weighed 0.19 grams. I am satisfied that these are premium BBs.

Getting the gun ready to fire

The Virtus AEG is a spring-piston airgun. It just uses an electric motor to rapidly cock and release the piston to simulate full-auto fire. That motor needs electricity to run, so the battery has to be installed in the forearm before the gun will fire. This step used to be extremely hard with the AR-15 airsoft guns I have owned, because the battery has to go inside the forearm that, on an AR-15, is not easy to remove or replace. But on the Virtus it is a snap!

 Virtus and battery
That battery has to go inside the forearm.

Knock out just one pin and the forearm slides off the receiver, exposing the connection plug for the battery. Remember, only the yellow plug on the battery’s longer cable is attached to the gun. The shorter battery cable is for charging, and doesn’t plug into anything while the battery is in the gun.

Virtus forearm off
The yellowish cable connector on the longer cable of the battery connects to the gun’s white plug. The shorter battery cable with the white plug is for connecting to the charger.

I must comment on how much room there is for the battery. On the AR-15s I have owned it was a real task to get the battery to fit inside the forearm and then get the forearm back on the gun. And on one gun the battery went into the A2 butt, which was a real nightmare. I hated it, which is the big reason I got rid of those AEGs. The Virtus is a walk in the park by comparison. I could easily fit two of these batteries in the forearm — one above and the other below the barrel.

Virtus forearm on
The forearm is back on the gun and pinned in place. The battery will fit either above the barrel like it is here, or below. There is plenty of room inside this forearm.

Now that the gun is ready to fire, it’s time to load it.

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Loading the magazine

The Virtus comes with an AR-15 lookalike sheetmetal magazine, and from my past experience these mags hold several hundred BBs loosely in the bottom. They get scooped up to feed through the gun and sometimes you get misfeeds. Nobody complains, though, because AEG airsoft guns are fired full auto most of the time. However, B.B. Pelletier doesn’t do things like others do.

I wanted to load exactly 10 BBs into the mag. and shoot them through the chronograph for velocity, then change BBs to a different weight. And that was how I became familiarized with the Virtus mag.

The 120-round Virtus mag has a spring-loaded follower that pushes the BBs up and into the path of the bolt. There is no chamber full of loose BBs. To load this mag you have to hold a spring-loaded catch back for each BB while the follower tries to push the BBs that are already in the mag back out. After fiddling with it for a few minutes I had to change my loading strategy!

Use the speedloader

The speedloader is more than a convenience with the Virtus. It’s a necessary part of loading the mag. I have more to say about it, but for now that’s it.

Virtus speedloader
Stick the nozzle of the speedloader into the nozzle of the magazine and start pressing the loading button on the speedloader.

The first BB I tested was the one Sig sent with the gun. We already know that they are very consistent.

I loaded four 0.20-gram BBs (the speedloader pushes in 4 BBs each time the thumb button is pushed down) into the magazine and then attempted to see what the velocity was. I then fired the gun on semiauto and nothing came out! Oh, oh!

The follower needs more BBs

What I discovered was the Virtus is fresh off the assembly line and needed a little breaking in. I put the selector on Rock and Roll (full auto) and let the bolt cycle many times. It was fun just listening!

I then loaded about 20 BBs into the mag to fire. Once that many were in it fired perfectly every time. And later — after perhaps 50 more shots, it fired all the BBs, even when loaded with just a few. Now that she is running, let’s see what she does.

Velocity 0.20-gram Sig BBs

First up were the 0.20-gram BBs supplied by Sig. On the box the gun comes in Sig says to expect to get 370 f.p.s. from the Virtus, so I was surprised to see that average of the first string reach 410 f.p.s. The low was 407 f.p.s. and the high was 413 f.p.s., so a spread of 6 f.p.s. That’s pretty tight.

Sound and feel of the shot

I was shooting semiautomatically, so each pull of the trigger produced a single shot. There was almost no motor noise, though I could hear the pop of air from the piston. I could feel some gearbox vibration through the pistol grip, but the only real sound was the pop of compressed gas from the piston. I have shot many AEGs and this Virtus has the quietest gearbox and motor I have heard. It’s even quieter than an AR-15 whose gearbox I rebuilt with upgraded steel bearings and gears. That one still had an air-wrench sound to it.

Rock and Roll

Since I overloaded the magazine for the first test, I went outside and dumped the remainder of the BBs on full auto. That told me there is no way I will be able to give you an accurate RPM count. This Virtus sounds like the infamous German MG42 “devil’s zipper” machinegun that had a high cyclic rate. I can count AR-15 cyclic rate up to around 800 RPM. This gun is faster than that. I have read reports of 900 RPM. It’s every bit of that!

More about the speedloader

Now that I was comfortable loading the magazine with the speedloader I found it quite easy to empty the contents of the speedloader to change the BB weight for testing. Just load the mag, then open the speedloader hopper pour out all the BBs except one. Since all the BBs were white and looked identical, this was the best way to keep track of them for the test. That last BB would remain in the nose of the speedloader until I pressed it out after the next BBs were inside. You do have that kind of control over the thumb button. Then that lone BB was returned to its proper container and everything was ready for the next test.

0.25-gram BBs

Given the higher velocity of the 0.20-gram BBs, I tried 0.25-gram Open Blasters from ASG next. They averaged 365 f.p.s. with a 2 f.p.s. spread from 364 to 366 f.p.s. These are going almost as fast as the gun is rated to shoot with 0.20-gram BBs, and it will be interesting to see how accurate they are.

Full auto accuracy

Since AEGs don’t recoil I indulged myself and went full auto during this velocity test. All the BBs stayed together in a tight group, though my target was only a few feet away. I need to find a way to test full auto in the accuracy test, too!

0.30-gram BBs

I then tried some 0.30-gram Blaster Devil BBs from ASG. They averaged 333 f.p.s. with a 1 f.p.s. spread from 333 to 334 f.p.s. This average is getting pretty slow, so I stopped testing here. Obviously a heavier BB will shoot even slower, but I think we have bounded the useful range of velocity in today’s test.

Trigger pull

An AEG operates with an electric motor, so pulling the trigger doesn’t release a sear like you might think. I will call this a single stage trigger, though the pull effort does increase after a lighter initial pull. The trigger “breaks” at 2 lbs. 2 oz. on the test gun and there is no hesitation of the trigger blade to alert you to the fact the gun is about to fire.

In the manual you are advised to shoot full auto in bursts to preserve the gearbox. You are told not to empty a 120-shot magazine on a single trigger pull. You are also instructed to return the gun to semiautomatic and fire it once blank after a run of full auto. That releases the mainspring in the gearbox. That is common for all full-auto AEGs.


This Virtus is stacking up very well at this point. It is outperforming another AEG that I custom tuned several years ago, so I am impressed. I hope it turns out to be accurate, though with a full-auto gun we aren’t looking for pinpoint accuracy. That’s not the way these guns are used.

Don’t forget there will be a second velocity test and a second accuracy test with the lighter mainspring after this test is concluded. So, there is a lot more to come.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

45 thoughts on “SigAir ProForce MCX Virtus AEG airsoft gun: Part 2”

  1. “I could easily fit two of these batteries in the forearm — one above and the other below the barrel.”
    Would it be possible to wire two of those batteries in parallel to lengthen your shooting time, or do you think it would not be worth the effort?
    Looking forward to the accuracy testing,

    • Dave
      If it fits it’s worth the effort in my opinion.

      Thats what we do with some of the electric RC planes to give more flight time. We just have to watch for the extra weight added to the plane. With the airsoft gun that little extra weight of another battery won’t hurt a thing.

      • Wow, an hour’s a long time; these days, I only shoot for 5 or 10 minutes at a time without a rest…
        …yeah, I know…I’m a wuss, hahaha! =)~

        • Dave and BB
          And another reason to maybe not add the extra battery is motor heat.

          The more battery time you have the more likely you are to shoot longer. Or in my case fly the plane longer.

          I’m always checking the motor heat and battery and speed controler heat when I fly. And another thing a lipoly battery will swell when its used. You should always let the battery cool down some anyway before your next charge time.

          Once I’m done flying with a plane it gets a cool down before its next flight and that being the speed controler and the motor.

          And notice I mention speed controler for the plane. That gives a throttle for the motor. Maybe a speed controler could get wired into the full auto gun. Then you could adjust your rate of fire. That could be a good tuning trick for the full auto mode.

          • An aftermarket option to some airsoft guns, they have computer controlled motor controllers.
            You can adjust rate of fire, (it always spins the motor the same speed, it just interrupts the timing cycle between shots to control the rate of fire.

            Ideally you want the motor to turn at a certain rpm so it develops the optimum torque to cock the spring without overheating, or drawing too much amperage.

            It can also be configured to give burst fire instead of full auto. (3 shot, 6 shot or so on)
            The gearbox of an aeg uses a gear with teeth only part way around the gear that cocks the spring and piston. When the teeth run out, the piston falls, the gear continues it’s cycle and picks up the piston again after it has traveled forward and fired the projectile.

            Here is a simplified animation of how the gearbox works.


  2. B.B.,

    For the full auto burst accuracy I would put up a target at the desired distance (10 meters?) then see how tight the group would be while aiming at a standard pistol target. Would all the shots remain in the black? Since prolonged full auto is discouraged I would not try cutting out a star.


    PS Section 0.30-gram BBs First sentence:
    “I the (then) tried some 0.30-gram Blaster Devil BBs from ASG.

  3. There is a way to test the rounds per minute accurately.
    Using your Mac or Windows laptop.
    You can record a short few second audio file of the gun firing on full auto.
    Then open the file with a free program called AUDACITY, that is used to mix/edit music.
    It will show the audio file in a graphic format with the audio having peaks at every shot as the piston slams forward, and you can count the peaks in 1 second, as the program has timing marks.

    It can be done in the house, as the gun can be empty when fired.
    As the rate of fire will only change with the spring pressure, and the state of charge of the battery.

    The projectile weight (or lack of a projectile) should have little or no bearing on how fast the electric motor cocks the gearbox.


  4. BB
    Siraniko sort of mentioned my idea.

    I was going to suggest a short video next time to do the full auto accuracy test. That way we can see and hear the gun shoot.

    I was going to suggest though to use aluminum foil on a target frame at 10 meters with a paper backer. That will show the bb’s that pass through as well as the ones that don’t pass through the target. It should show dents and the bb’s bouncing off. It could be a penetration test too.

    • And thinking more.

      When they are doing their airsoft wars. How far away is their opponent? 25 yards?

      So maybe the full auto blast is suppose to represent a shot gun blast so they can get a hit.

      Just a thought. Curious to see what kind of pattern a full auto blast would look like out at longer distances. Maybe I’m off base on that thought but then again maybe not.

      • The average engagement distance depends on several things.
        The capabilities of you and your weapon, and how well you know it’s accuracy and range.
        And the terrain.
        Thick southern overgrown woods gives a shorter gameplay than open forest or grassy openings.

        Some spring powered sniper Style rifles Can go 75 yards or more easily.

        And you only have to get 1 hit anywhere on the body to be out of the game.

        But I will say I have had no issues with sending shots at 40 yards.

        Remember, you miss 100% of every shots you don’t take.

        On the receiving end you don’t hear the projectiles coming.
        As the guns firing cycle are not that loud.

        Now if someone sends a burst and the leaves on the bushes around you start to get shredded it will get your heart rate up.


        • Ian
          Yep that all makes sense.

          I know the sniper air soft rifle I had with the heavier spring did shoot good out to 35 yards at aluminum cans. I and I could hit a 1 gallon plastic milk jug at 50 yards with it.

          I like semi and full auto guns. I wanted to give a full auto air soft gun a try but just never have. I’m sure I could have fun with it.

          • GF1, Contact me by EMAIL OR PM through Gta.

            If you pay shipping, both ways, I will loan you one to try,
            It’s not an expensive one, but it’s reliable.
            And reasonably accurate out to 35 or so yards.

            It’s retail price is in the $150 range.

            I bring it out at family gatherings and let kids and grandkids burn all the ammo they want.

            While learning safe firearms handling.


            • 45 Bravo,

              Nothing like,…. “While learning safe firearms handling” and full auto being an option! 😉

              Chris (I needed a Grandpa like you growing up!) 🙂

              • I have never met ANYONE that didn’t have a HUGE Smile on their face after dumping a magazine or a part of a belt from a full auto weapon.

                It doesn’t matter if it was real, or an airgun.

                The popularity of the Umarex Legends series is testament to that.


              • Growing up, one of my dads friends had several machine guns.
                When he passed away, his son, inherited them, the transfers were easy, as his dad made sure he had been owning NFA weapons since he was legal age to do so.

                He wrote software for Atari back in its hey day, so could afford all the NFA toys.

                So in my adult life, I have been privileged to enjoy a wide range of his collection.


              • Here ya go,
                Not my photo, but it is my theory on what kids should be taught and exposed to.

                You never know what you may encounter, and need to handle it or secure it safely.

                • Ian
                  Great picture. That’s what I think too. My daughters learned too about shooting and such at a young age. Just like I was taught. Now I have my first grandson that is 5 months old at the end of this month that will be taught as well. I’m looking forward to that too. For sure.

            • Ian
              Thanks for the offer but heck for a 150 bucks I’ll buy one. And you said the two magic words reliable and accurate.

              What one is it your talking about and what weight ammo are you using in it?

        • 45Bravo,

          Ian, you don’t hear the real ones either until they already next to you, or in you, or past you! Unlike most Hollywood pictures have the sound effects timed out. I have no experience with airsoft skirmish is the ear/hearing protection the issue? Could high quality electronic 3D Mick-Mouse Ears let you hear the Pop B.B. discribes? Not being able to hear where the rounds are coming from is harder to do with firearms. In urban areas and villages with hard structures it sounds like the rounds are coming from everywhere unlike in jungles and bamboo structures which is another set of problems all together. Took a while to adjust to potential true cover vs just concealment!
          I think it would be fun to design an airsoft area with some reality built in! Shot anywhere and your dead (probably for some length of time before you regenerate)…nah! You need the added problem of your team members crying out for help!!!!! Points off for leaving them on the field….


          • On the field, there are lots of shots going on at any given time, both outgoing, and incoming.
            Differentiating between the two is often difficult.

            Fire discipline is unheard of, as most of the players figure if anything is worth shooting once, itw worth shooting 30 or 40 times.

            Most inexperienced players leave the guns on automatic, and fire a extended burst towards their target, and adjust the point of impact as they walk the stream of projectiles onto the target.

            I have used stereo phonic hearing protection before for hunting, but not in games, and i believe it would help with what direction the pop happened, if things were slow on the field.
            But I have never been in a game where things went that slow, once your side found the other side, any plan you had, went straight out the window.

            That being said, there are very serious Mil-Sim games that draw a lot of exmilitary guys that enjoy the rush, with out the potential death part getting in the way.

            Some are actually held with the support, and encouragement of local National Guard or Army assistance.

            Airsoft guns are great for force on force training, as you have the ability of actually shooting at your adversary, (and being shot at) without brining a real weapon, or a simunition weapon on the training field.

            With airsoft guns, and their power levels, by the time you get out to 50 yards, the .20gram bbs are sticking in cardboard rather penetrating it, so concealment actually becomes cover.

            I would suggest looking up a few videos on youtube, a thousand questions can be answered, and a thousand more generated.


            • 45Bravo,

              Thanks for that info Ian! Especially the “serious Mil-Sim games” ill be looking at more on that for sure. Not much more to do just now in this enforced spare time when the weather isn’t good enough to shoot or kayak…TV has never captured my interest!

              Thanks again,

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