If you are going for a silent build what other modifications are you doing?
The AUG I have with that headset is set up to be quiet. I can shoot it in the house and it can't be heard downstairs. On the battlefield, you can fire full auto and it's extremely hard to pick it out unless you are right on top of me.
The components that went into the gearbox were picked to avoid and disrupt as much noise as possible.
Single tooth plastic piston.
Brass spring guide. Single plastic spacer, no bearing. (mines a deepfire). Use the bearing on the piston head.
Greased mainspring.
Shimmed with brass shims and greased with really soft moly grease.
Full brass cylinder.
Stainless bushings.
The idea behind the build was simple enough. Use as many different materials, and get them as thick and solid as possible. Nothing should rattle or act like a tuning fork. You'll never get the gearbox silent, but you can dull the higher sounds using as much mass as possible so any vibration to sound is a lower note. Low frequency travels further, but it does so with far less energy and is far harder to pick out over background noise.
The mass of the piston head should be watched however. If it's a heavy head they have a tendency to clack. Lighter heads like the element ones have more of a wet thud, and that in combination with the extra gearbox mass is where the sound reduction is made.
A cheap foam filled moderator is also beneficial as it will disrupt the noise coming out of the barrel. A cheap unit with the spring and foam at about 100mm is more than enough to have a significant effect.
