Here I come again, cape a fluttering and bright red underpants over the top of my combats
Consider this an edit to my SPR post

I didn't mention motors and probably should have :-[ Anyhoo... Two of the quietest motors on the market today are..... TM EG700/1000. I personally think the EG1000 is quieter but not by alot, I tested them side by side and now an EG1000 resides in the grip of the SPR ( set the motor height tonight and it is really quiet now
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To go further into 2echos' question, I would recommend trying to source an SPR hand grip, They have about twice the thickness of plastic/nylon/resin compared to a stock grip which will insulate the sound a bit better( a word of warning though, they are right handed only, no good at all if your a lefty). Silent piston heads are crap and are only silent in name only. Your best bet is Sorbothane, a rubber compound that comes in a variety of hardness', stick to the harder compounds as the soft ones are just that

stick a layer on your piston head and a layer on your cylinder head and you have approximately what I have got just stuck to my cylinder head

The next thing to do is fill all the voids, use sponge or soft foam, in different thickness', so you can push into any gaps, the largest gap you will encounter is in the stock * and the space between the front of the gearbox and the inside of the delta ring, either side of the hop chamber, but remember not to fill any lower than the feed tube. * (If your an M16A1/M4A1 owner it will be the foregrip

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The Airbrake piston is still a viable option, and has the most dramatic effect on noise levels, it would just mean you would need to install a higher rated spring as on average you loose 20/25fps from this mod.(You must be careful though if you use full auto with an air brake as it slows the return time of the piston and could lead to premature engagement of the piston, with the resultant zip, bang ,whirrrr.....

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And finally, like everyone else has recommended, a suppressor, if your lucky enough to be able to use foam filled ones, do it

. To further improve performance make the inside of the foam as random as possible and fit baffles, like these
at random distances down the length of the silencer. The hole should be no smaller then 9mm in the baffle and you should make sure that they all run in line, easier said than done I can assure you

. The basic principle is to trap the sound wave behind the baffle and give it somewhere to expand to and die off then on to the next compartment which is slightly smaller/larger and this then dampens the sound at a different octave level and so on.... down the silencer until there is very little of the muzzle pop left with enough energy to make to much of a noise about.... did you see what I did there, I should be writing comedy scripts
Thats all I can think of at the mo that I haven't already covered in the SPR post, but if I think of anything I'll post it here.
VA
EDIT
Oh yes, Barrels, if you have a brass one, try cleaning and then and then polishing the crap out of it then send about 200 rounds down it to bed it back in. Seems to work on this 6.08 I have in the SPR, but it was windy as hell here today so quite hard to get solid results. Short of that a nice tight bore of 6.04/6.03, I got a madbull black python in the EBR and they are resonable but not the shizzle
