[BlackDogAirsoft]

So based on 1tonne's post about AUG, as long as we have a gun with enough space to fill with enough foams, we can make something as quite as his AUG?

Yes, so long as you do the other stuff- spiral gears, airpad (better than sorbo) etc.
Also, surely if you desire a compact quiet sniper rifle, a mk23 based carbine would be the best option?