AEG Silencing Guide

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AEG Silencing Guide

Post by surefire pigeon on Mon Jul 25, 2011 1:00 am

A.E.G. Silencing Guide

This is a how-to on how to make your electric gun much quieter. Most of the noise comes from two places - gearbox noise and barrel pop. I will be discussing both.

Gearbox Noise

Shimming – Make sure you shim according to the bevels gear interaction with the pinion. You do not want the pinion to forcing the bevel up or you will get a nasty screech regardless of motor height. When you shim, polish your gears and remove (gunk) that collects in between the teeth to prevent binding. Shim your gears tight, but not too tight, to the closest .01mm. You want to have VERY minimal play to prevent gear slapping, but want them to spin freely.
Gears – You will want to break in you gears at a slow speed. Additionally polish them as I stated before.
Motor – Breaking in your motor (if it is not stock) is also a good idea. Choose a soft pinion, like a Tokyo Marui or G&P. They will wear faster at more strenuous levels, but will decrease gear whine substantially.
Piston POP – Do not opt for a metal piston head. A polycarbonate will save a loud crack as well as save a crack in the gearbox. Using Sorbothane Padding with a buffer can absorb shock and in some cases quiet the gun. Use 70 durometer for greater than 1 joule. Using 50 durometer can have better silencing effects but should be used for gearboxes with a m90-m100 because it will change more at higher shocks.
AR Latch – If you plan on using a semi only weapon and are utilizing an active-breaking MOSFET, you CAN remove the AR latch. I DO NOT recommend it but it will prevent a fast clicking nose.
Lastly, Grease Well – I use a silicone gel with Teflon called Superlube grease. Use it for the gears, bushings, and the cylinder. Use 20-30 weight Silicone Shock oil for the tappet, and piston rails, as well as the piston and cylinder head o-rings. Greasing the gears will allow them to run smoothly and efficiently, while greasing the other parts is always a good idea.

Barrel Pop
– Most of the noise from barrel pop is a result of the air behind the bb expanding rapidly.

Barrel Extension – By using a hollow barrel extension such as a homemade PVC one, you can fill it with material to help absorb the sound. Using cotton or foam is best, as it is easy to mold and does its job well. Please be aware that if it can be at all capable of being modified of being mounted on a real gun, be it through barrel threading, friction fitting, or any other way, it is illegal if it can reduce the sound by even one decibel for one shot. So to be legal, any non-hollow barrel extensions are to be permanently affixed to the airsoft replica in question.
“Expander” - I have not tried this yet, but in theory, should work well. The concept is a barrel extension that as the farther down you get, the wider the bore will be.
This will allow the air to expand slowly, thus reducing a popping noise.

These are my suggestions, if you have any other suggestions, post a reply and I will add. Hope this benefits anyone who is trying to quiet their AEG!

surefire pigeon

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Re: AEG Silencing Guide

Post by DHM078 on Tue Jul 26, 2011 2:23 am

Thanks for posting this. But I do have a few of my own thoughts to throw out there.

I think you're over thinking shimming when you start assigning valves like within 0.01mm of play. Seriously the smallest shims sold for airsoft purposes are 0.05mm. Most shim to about 0.1mm. You can get them smaller if you know where to look, but it's really unnecessary. Just shim so the parts mesh well, there's no notable play, and it isn't so tight it adds resistance.

Breaking in the motor isn't a bad idea, but it will not make the gun any quieter. It just wears in the brushes, which has pretty much no impact on the noise the motor produces.

Another thing that goes a long way in reducing the sound of the impact is compression. The air build up in front of the piston slows it slightly. You may not think it would make a difference, but compare the sound of a gearbox with no piston head o-ring with a properly sealing one. Big difference. Heavy ammo contributes as well. Its mass allows it to stay in the chamber longer, meaning more of a pressure build up.

I strongly recommend that you do not under any circumstances remove the anti-reversal latch. The noise it produces is minimal and doesn't carry well, and the risks from removing it are substantial. Even active braking isn't enough to stop completely. ASM in general seems to be moving away from active braking due to its relative inefficacy and the stress it puts on the battery and motor.

While I do like that Superlube stuff, I still suggest white lithium grease for the gears. It's just slicker.

Silencers/suppressors are illegal and discussion of them is thus not allowed. So I have modified your post to make it legal.

Simply using foam, or another "sound-absorbing" material inside will not be as effective as you might think. That is because the low pressure air escaping is not being forced into the foam. Anything the foam accomplishes is done at the surface only. Therefore, for airsoft purposes, it is better to have more surface area, by having foam "ribs" for lack of better term. See the pic below for clarification:



Obviously, the longer the extension area, the more effective (of course, there is a point of diminishing returns).

I have my doubts as far as the "expander" you mentioned. To be fair, I have never tried anything like it though. But there really isn't enough air to warrant it, and there isn't much pressure behind it at the muzzle.

Another thing to note is that longer barrels tend to give a quieter "muzzle blast" if you will, because of the increased expansion room within the barrel. Even properly volume matched, a gun with a shorter barrel relies on using a low-volume high pressure burst of air which expands much more suddenly within the barrel. The longer barreled guns have more space to accelerate the bb, and thus the air leaving the cylinder is at a lower initial pressure and loses its pressure more gradually since it accelerates the bb over more distance.

In any case, using a cylinder that is actually under-volumed should in theory reduce that air pop significantly, although it would come with a loss of power. The difference it makes both in sound and power obviously depend on how low the cylinder volume is.
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