Boring question #78; sonics aka silencers are they that quiet really or does size matter?

The mythbusters did an episode on that recently.
“Silencers” do not make gun shots quiet. Just a bit less loud.

After the bullet leaves the barrel of a rifle or pistol, the expanding gas that pushed it out then follows it, at a pressure that may be in the order of 3000 psi. This is because the volume in the gun barrel confines it. The sound of gun shot is the same principle as the pop you hear when a cork comes out of a champaign bottle.
A silencer allows the gas to expand dramatically after it exits the barrel but before it hits the air. This decreases the psi dramatically- often to below 100 psi. Sort of like when you put a towel over the champaign bottle before you work the cork out.
The result is not no sound at all to be sure. But at a distance, it can be tough to hear. And even close up it becomes a sound that is not readily identifiable as a gun shot. It also obscures the exact location of the gunshot, which is half the battle in some cases.
The bigger the silencer, the more the gas can expand in the chamber, the lower the pressure when it hits the ambient air.

They never show these spies doing maintenance on these weapons. And boy do they require a bunch. All those gasses being temporarily bottled up is causing a lot of crap to go back inside the guns workings and they will fail sooner than the guns without the cans. Hollywood…gotta love em.

The correct term is suppresor. Silences is a misnomer as it is nearly impossible to completely silence a firearm. Even when fitted with a suppressor, the operator still typically has to wear hearing protection.