How to make the quietest AEG ever

Discussion in 'Gun Building, Modifications & Repairs' started by 1tonne, Sep 4, 2018.

  1. 1tonne

    1tonne Well-Known Member

    New Zealand
    After years of trying to make the quietest AEG ever, I now have the knowledge to make the quietest AEG ever. This rifle will be quieter than the Mk23 Socom pistol which is renowned for stealth.

    There are 5 areas of sound that you want to lessen. First the sound signature of the rifle (Length of sound). Next is the squelching sound (Gearbox Noise). You also want to get rid of the spring sound (Twang). Stock vibration also and lastly is the muzzle sound (piston slap noise exiting barrel).
    Of these 5 areas, the hardest one to eliminate is the squelching sound from the gearbox. Gearbox's that have a motor cage are the easiest to reduce the squelching sound as the motor should be trapped in the correct position all the time. Gearbox's like in the M4 are a lot harder to reduce sound as the motor can move a little off alignment.

    To make the quietest AEG there are 22 points you will need to work on. Here they are

    1. Air seal - When you have a good air seal you can use a weaker spring because you do not have as much waisted gas. The areas to check are O-ring seal, Cylinder to cylinder head, air nozzle to cylinder nozzle, air nozzle to hopup bucking and lastly, hopup bucking to barrel. Most of these can be fixed rather simply. The hardest is the seal between the air nozzle and the bucking. To seal between the air nozzle and the bucking properly, check out number 13 further down the list.

    2. Spring- Thread on little bits of heat shrink about 10mm long to your spring at each third and shrink them. This will help stop vibration and get rid of some of the twang sound.

    3. Barrel Bore size- The tighter the bore, the easier to get higher fps which means you can use a weaker spring. This means less stress in the gearbox.

    4. High Speed Ratio Gears- The quicker the sound is the less your ear will be able to register it. So if you use a high speed gear ratio of at least 14:1 or less (I used 13:1) the rifle will be very snappy. Also these types of ratios have less squelching sound. (High torque motors go well with high speed gears)

    5. Use a LONEX Spiral Bevel & Pinion Gear Set- These gears have curved teeth that allow for better meshing of the pinion to bevel gears if your motor is slightly at the wrong angle. This is common in V2 gearboxes as the motor is not in a motor cage.

    6. Piston Weight- Make your piston as light as possible by drilling holes in it (this is called Swiss Cheezing your piston). This will make it easier for the sector gear to pull it back meaning less squelching.

    7. Cylinder head cushion- Use Sorbathane as a dampener on your cylinder head. This will lessen the piston slapping sound.

    8. Choose a cylinder that is smooth on the inside- Some cylinders have ridges that are designed to help keep the cylinder lubricated. The issue with these ridges is that they create more noise as the O-ring goes over them.

    9. Use extra thick lubricant on gears- Thicker means it stays on- Less friction which means less squelching noise.

    10. Use bearings- Bearings make for an easier cycle. The easier the cycle the less squelching noise from your gearbox.

    11. Use gears that have in built bearings- Makes for easier cycle

    12. Shim correctly- Lessens the gearbox squelch sound

    13. Use an air nozzle that is about 1mm longer than normal or sand the front of the tappet plate so that the air nozzle moves further forward than normal.
    NOTE: Sometimes this can cause feeding issue. Retro Arms put out adjustable air nozzles that can help.

    14. Use the biggest battery possible- Lessens gearbox sound signature. You do need to be careful though as sometimes this can create more high pitch squelching

    15. Use the correct cylinder to barrel ratio- This is one of the most important, if not the most important thing to do when making your rifle quiet. If you use the correct ratio, then you are making your rifle the most efficient that it can be which means you do not need such a large spring to get your desired fps. Also, there will be no extra air being pushed out of the barrel that carries the sound of the piston slapping.

    Here are the correct Ratios to make your rifle quiet: (Ratios for a 6.03mm)
    BB weight--- Ratio
    NOTE: If using a 6.01mm, then you can use a barrel up to 25% longer as there is not so much air lost around the bb.

    For all the information you need to know about cylinder to barrel ratios, read this thread that I wrote (It is a must read):

    16. The longer the inner barrel the quieter- A longer barrel will produce higher fps so you can use a weaker spring (Less gearbox stress). The disadvantage is that it can make the rifle too long. A bullpup can be good in this instance as the inner barrel can run from the back of the rifle where the magazine is to the front.

    17. Use a silencer- This captures the excess sound that is travelling behind the bb. Without a silencer your rifle will be a lot louder. This is expected though as the perfect ratio will have just enough air to push the bb out of the inner barrel. Even though the bb is out of the barrel and there is no excess air pushing the sound out of the barrel, there is still has a negative pressure at the rear of the bb. This negative pressure may drag the excess sound behind it. This excess sound can easily be captured by a silencer. So an airsoft silencer can really work if done correctly.

    18. Silencer Length- Different silencer lengths can have different effects on the sound that comes out of the end. A silencer can be too short or even too long. So experiment with different silencer lengths or use a shorter outer barrel so that the inner barrel sticks into the silencer more. This will have the same effect as using a short silencer.
    I originally used a silencer that was long (243mm long) and it made the rifle louder and so now my quietest AEG has a silencer that is only 173mm long.

    19. Silencer Muzzle Hole Diameter- A normal airsoft silencer muzzle hole is about 12mm in diameter. If you put washers that have an 8mm hole between each piece of foam, the muzzle sound should be more trapped inside the silencer in each little compartment. You do need to be careful that the bb does not skim one of the washers as make the gun inaccurate.
    But be careful as you will need to experiment. On the odd occasion, modifying a silencer like this can increase the sound.

    20. Try different materials in the silencer- Different materials will reduced the sound waves differently. Also try the material compressed into the silencer and then not compressed. Different rifle setups will produce different sound waves. So experimenting is key here.
    In my AUG, I used a white fluffy material that is used for sound deadening in buildings. I rolled is up around a spring to keep the fluff away from the bb.

    21. Use Dynamat Sound Deadening- Put Dynamat sound deadening in as many places as possible. In an M4, there is not many places to use it as the M4 has very limited space. On an AUG, you can wrap the gearbox in it and put it on the inside walls of the stock.

    22. Fill empty spaces- Fill any spaces in the rifle, especially the receiver with sound deadening foam or fluff. In an M4, there is not many places to use it as the M4 has very limited space. On an AUG, you put it between the gearbox and the stock walls.

    23. Semi Auto- Use semi auto as it gives a shorter sound signature than full auto

    24. Motors can also add a lot to noise. A motor with an unbalanced armature or a slight bend in the shaft will vibrate more. This will make noise between the pinion and bevel gear as it will not have a consistent meshing

    Here is what my rifle has:
    -Army Armament Styre AUG
    -SHS Ultra high Torque motor
    -Super Shooter 13:1 gears
    -M100 Spring (Producing 350fps) (Heat shrinked)
    -Full Cylinder: Ratio = 2.18:1 for 0.25gm bb's
    -Barrel: Action Army 510mm x 6.01mm
    -Air Nozzle =Stock (24.75mm)
    -G&G Green bucking
    -Sorbathane on cylinder head
    -Piston: G&G Polycarbonate with a single metal tooth (Swiss cheesed)
    -Piston head: G&G Plastic
    -Bearings: Can’t remember the brand
    -Silencer: 173mm x 40mm with foam inside (Round washers with 8mm hole inside)
    -11.1v Lipo
    -Dynamat on gearbox and inner stock

    NOTE: To test if the sound is coming from your muzzle, put the receiver between 2 pillows with the muzzle sticking out and fire it with the desired bb weight. If you want to test the gearbox noise, just put a thick rag over the end of the muzzle and then cover the muzzle with the pillows and fire with the desired weight.

    NOTE 2: I tested the sound in a similar way to how a lot of other rifles are tested. This is with the decibel meter 1 meter to the left of the barrel, at a height of 1.6m (standing shot) and the microphone pointed straight up at 90 degrees to the direction of travel of the bullet (to eliminate projectile pressure).

    So I measured the sound of my quiet rifle and I also measured a couple of other rifles too. A G&G CM16 and also a short barrel Ares Amoeba. This is a short stubby loud gun.

    Check out this video:

    Quiet AUG = 72.93dB (78.2dB without silencer)
    Quiet M4 = 78.53dB
    Mk23 Socom = 79.43dB
    G&G CM16 = 85.2dB
    Short Ares Amoeba = 87dB
    .177 air rifle = 88-90dB (Taken off another website)
    Last edited: Aug 4, 2019
  2. link0

    link0 Well-Known Member

    SF Bay Area
    I would like to add that full cylinders + long barrel is ideal for reducing noise. The reasoning is that the BB is gradually accelerated along the entire piston travel on a full cylinder. All of the energy from the piston is transferred into the BB rather than being wasted through the port.
    BOA_SP3CT3R, -Spitfire- and 1tonne like this.

  3. 1tonne

    1tonne Well-Known Member

    New Zealand
    That is correct. So you do not need such a big spring to get the desired fps. So less gearbox stress and noise.
    Though, long barrels can be a pain. The rifle I made can be used in a green role type of game and is also short enough that it could be used in CQB effectively.
  4. Lefse

    Lefse Well-Known Member Supporting Member

    Not quite, the energy from the spring is "stored" in the piston as kinetic energy and isn't necessarily wasted through the port. My AK-104 with a 247mm barrel is getting close to the same compression efficiency as my AK-74 with a 455mm barrel, this would be impossible if any energy was wasted through the port.

    They both have the same spring and the piston assembly weighs the same. If I adjusted the porting of the cylinder in the shorter barreled AK it would have the same compression efficiency as the longer barreled one. We're talking about a difference of maybe a few percent as it is though.

    It's true that shorter barreled AEG's tend to be slightly louder though, my G&G M4 with a 170mm barrel is extremely loud.
    1tonne likes this.
  5. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

    And longer is not always better.

    Issue is these are blow guns not firearms.

    Long barrel and weak spring = low fps.

    The Only reason why it's quieter is that the bb is decelerating in a barrel that is to long for the pressure wave generated by the piston in the cylinder.
  6. Jeranhound

    Jeranhound Active Member

    I believe that he means that, for silence, it's better to use a longer barrel at the same energy so that you can use a softer spring and take advantage of the greater barrel volume. The idea being that you're not applying extra brute force to make up for any inefficiency. He's not saying the longer barrel performs any better, just that an ideally volumed system can be quieter than an overvolumed one.
    1tonne likes this.
  7. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

    Okay...true on the last part.

    If you really want to make your gun quiet...port the barrel.

    And I use old school paintball as an example. Ported barrels are much quieter than unported barrels.
  8. the airsoft scientist

    the airsoft scientist Active Member

    Just like to ad that you shouldn't be too generous with lube since over living can cause leaks in the cylinder. It's happend to me a lot when I first started teching
  9. the airsoft scientist

    the airsoft scientist Active Member

    Where do I port it? I have a 380mm x 6.03mm
  10. BOA_SP3CT3R

    BOA_SP3CT3R Moderator Staff Member Moderator Supporting Member

    Bull Shoals
    The very end. Look at the ported EdGI barrels.

    To add to the original post:
    Not only low ratio gears but a motor with the correct TPA. My SCAR uses 15:1(13:1+9 tooth bevel) gears and a Tienly 16tpa motor, there's almost no noise coming from the gearbox. That's mostly due to the shimming, gear meshing, ZCi enhanced bushings, Airpad and short stroking(8 teeth!). Better quality bushings like ZCi enhanced or FLT have very little room for the axles to wobble and can be just about as quiet as bearings.

    Sorbothane wears out too easily, though it should be ok with that weak of a spring. Airpads are very durable and give a low pitched sound. They also reset instantly after being compressed while sorbothane takes 2 seconds.

    Another thing I've been seeing lately is the Lonex spiral pinion and bevel sets. They apparently make very little noise.

    But thanks for some of those tips! I might build a gun solely for the purpose of being silent and accurate.
  11. link0

    link0 Well-Known Member

    SF Bay Area
    I agree that only a very small amount of energy is wasted through the port (the piston picks up most of that energy in gathered momentum until it reaches the port end.
    kazuchan and 1tonne like this.
  12. 1tonne

    1tonne Well-Known Member

    New Zealand
    That is one thing I really wanted to do but the cost of a freight for an Edgi barrel to get to NZ is ridiculous. The idea being that any excess gas would be directed through the ports and into the silencer. In saying this, it probably does not need the ported barrel as there is nearly no muzzle sound anyway. I also wonder if it would work in a rifle that is correctly matched cylinder ratio as the idea with the porting is to release any extra gas up through the ports but with a correctly matched ratio there is no excess gas to be pushed through the port. Also, once the piston has completed it's cycle, there is no extra air to push the sound out of the barrel so my presumption is that the negative pressure behind the bb is dragging some sound out of the barrel. This negative pressure would not push sound out of the port but suck air into the barrel through the port from the silencer.
    On a paintball gun it would work though as they are not 100% matched with the gas ratio. The excess gas would go out of the ports.
  13. 1tonne

    1tonne Well-Known Member

    New Zealand
    Just added a note as the bottom of the original post:
    NOTE: To test if the sound is coming from your muzzle, put the receiver of the rifle between 2 pillows with the muzzle sticking out and fire it with the desired bb weight. If you want to test the gearbox noise, just put a thick rag over the end of the muzzle and then cover it with the pillows and fire with the desired weight.
  14. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

    You are misunderstanding the role of the port.

    The Port mitigates gas pressure so the rapport is reduced from the muzzle.

    And your analysis of an Airsoft bb as it travels through the barrel is too simplistic. You are using an on and off model when in fact it is a system of dynamic pressure waves that start increasing from the pistons initial movement and stops after the piston head bottoms out. That movement creates a pressure wave inside the barrel that will exspell a bb out front for the barrel. Light spring slower longer wave. Heavy spring faster shorter wave.

    The point you are missing is the Movement of air transfer from the cylinder to the barrel. Having an equally matched volume to barrel ration means this does not Stop the movement of air in the form of a pressure wave from the cylinder to the barrel, you are still creating a wave.

    The only way the AEG will make no sound from a bb leaving the barrel is when you have barely sufficient pressure to clear the bb from the barrel and that would mean having practically no air in the cylinder when it bottoms out.

    Plus there is no barrel suck, the system is not closed and unidirectional piston heads mitigates air draw from behind the barrel to put back into the cylinder.

    Try this. Fire a bb out the barrel and notice the sound volume is lower than the same AEG dry firing. This is how experienced players know when to move from under fire...when the sound of an empty AEG is being made (louder) they know it's safe to move.
    Last edited: Sep 4, 2018
  15. 1tonne

    1tonne Well-Known Member

    New Zealand
    I understand that the ports let out excess gas

    Understand that too. That is how I look at the pressure in the system with different springs. The perfect ratio is when the bb leaves the barrel with the most energy. This may have some excess gas still left in the barrel. This excess gas is captured by the silencer. The silencer is one of the key things here.

    From what I see, I do understand the movement of air from the cylinder to the barrel. I may not have explained myself enough though.
    Piston starts to move - Pressure builds up - Piston finishes cycle - there is still pressure in the barrel once the piston has finished moving. This pressure then expands back to normal as the bb is pushed through the barrel.
    As the bb leaves the barrel, the high pressure gas should be mostly used up if the ratio is correct. Leaving very little excess gas. This is where we need a silencer as there may be a little bit of excess gas but very little.

    The perfect ratio gets you the most energy. This does not mean it uses all the gas. There may be a little gas left.
    If it bottoms out, and you were to go over the perfect ratio, it does not matter because there is no suck back effect. The perfect ratio just gets you the most energy for that bb. Once you go over that ratio the energy will be lessen. (The pressure will be decreasing as the pressure in the barrel evens out. This is what is caught in the silencer.)

    I agree that there is no suck back effect. Though once you go past the optimum ratio, you do start to lose a little energy as there is nothing to propel the bb forward. There is also a lower pressure behind the bb than what there is in front. Even as the bb goes through the air, there is a higher pressure at the front.

    Firing an AEG with no bb in it is similar to an over ratioed system. So it will be noisy.
  16. link0

    link0 Well-Known Member

    SF Bay Area
    This thread needs way more videos. I want to hear how quiet these AEGs are back-to-back with standard stock AEGs like a CM16.

    My AEG's are generally pretty decently quiet without a silencer. Most of my noise is coming from the piston slamming into the cylinder head (I use a Danco hard rubber faucet washer + a slightly softer neoprene washer on my cylinder head for AOE correction).

    I suspect it would be very hard to hear my AEG from past 150 feet.
    1tonne, Chow and papasmurf08886 like this.
  17. cetane

    cetane Well-Known Member

    Markham & Stouffville, Ontario, Canada
    Funny to see that posted. I’ve got a set on route. I’m thinking in my ump with a 16:1 step & dsg. 8 motor rotations per shot not too bad... going to “shoot” for a goal of 330-350 fps at whatever rof ends up with a 24-27tpa motor on 11.1
    1tonne and BOA_SP3CT3R like this.
  18. 1tonne

    1tonne Well-Known Member

    New Zealand
    150 feet is very good. Similar to when I shot beside my son and he did not notice until the 4th or 5th shot.

    If I get time I will post up a video. I have previously done one a couple of years ago where I made an SR25 very quiet. It registered on the decibel meter as only 88dB. Check out 1Tonne Airsoft on YouTube (There is only a few vids)

    I find the hardest part to make quiet is the gearbox and motor. The muzzle sound is easy. Just match the ratio and use a silencer.
    link0 likes this.
  19. link0

    link0 Well-Known Member

    SF Bay Area
    Found it:

    1tonne likes this.
  20. 1tonne

    1tonne Well-Known Member

    New Zealand
    I just did one more alteration that has brought the muzzle volume down 1dB. So it is now around 87dB. All I did was make up a washer to fit in the silencer that has only an 8mm opening for the bb to pass through. (I will add this mod to the first post. PS I know this is nothing new but it helps).
    I also did a side be side listening test of the Mk23 Socom and the quiet M4. The result when listening to the 2 guns is that the Socom still sounds a little quieter even though it is registering about 5-6dB more on the decibel meter. I presume the reason for this is that the sound coming from the Socom is a deeper sound than the M4. Lower frequency noises from what I have been told are harder to hear or distinguish while the M4 gearbox has a higher frequency.
    Now the Socom also does not have a gearbox and so the only noise is the muzzle sound. I just tested the Socom muzzle sound on the dB meter came out as 92-93dB at 20cm away.
    Since there are 2 areas that make noise on the M4 I decided to test both the muzzle sound and then the gearbox sound. With the muzzle 20cm away from the dB meter, it registered at 87dB. I then held the receiver over the dB meter about 20cm away and it registered at 91dB. So both the muzzle and gearbox sound register quieter than the Socom.
    So even though the M4 is registering as a quieter rifle, the Socom is the harder one to hear. In game both guns will be very stealthy though and should be a lot of fun. I can hardly wait until the next game.
    adas1223 and BOA_SP3CT3R like this.