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.
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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
0.2gm-------2.13:1
0.23gm-----2.15:1
0.25gm-----2.18:1
0.28gm-----2.20:1
0.30gm-----2.23:1
0.32gm-----2.31:1
0.36gm-----2.43:1
0.40gm-----2.61:1
0.43gm-----2.68:1
0.45gm-----2.76:1
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): https://www.airsoftsociety.com/threads/what-barrel-length-goes-with-what-bb-weight-in-an-aeg.153191/
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:
So:
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)
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
0.2gm-------2.13:1
0.23gm-----2.15:1
0.25gm-----2.18:1
0.28gm-----2.20:1
0.30gm-----2.23:1
0.32gm-----2.31:1
0.36gm-----2.43:1
0.40gm-----2.61:1
0.43gm-----2.68:1
0.45gm-----2.76:1
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): https://www.airsoftsociety.com/threads/what-barrel-length-goes-with-what-bb-weight-in-an-aeg.153191/
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:
So:
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)
