I have a foam filled supressor on my Echo 1 P90, and it actually muffles the report significantly. It comes equipped with an aluminum piston head, and has a very loud crack. With the supressor, the muzzle report is deadened significantly making the motor / gears really the only thing you can hear at a distance. This has been witnessed by many surprised observers at the Mill on my 2 occasions there, and again this past weekend at a game where I compared it to a couple of TM P90s. The supressor makes a huge difference. It certainly won't make one stealthy, as the motor sound will give away the fact someone is shooting, but will kill muzzle report.