What gun cannot be silenced, due to all the noisy gasses which escape the cylinder gap at the rear of the barrel?

A suppressor, sound suppressor, sound moderator or silencer is an accessory device that is attached to or part of the muzzle of a firearm or air gun’s barrel and reduces the noise signature (muzzle report) and visible flash generated by the gun’s firing.

A revolver is a repeating handgun that has a revolving cylinder containing multiple chambers and at least one barrel for firing. Revolvers might be regarded as a type of pistol, or as a subset of handguns, distinct from pistols, which in this case are defined as handguns with a single chamber.

A suppressor can only affect the noise generated by the two primary sources – muzzle blast and sonic boom – and in most cases only the former. While subsonic ammunitions can negate the sonic boom, mechanical noise can be mitigated but is nearly impossible to eliminate. For these reasons, it is difficult to completely silence any firearm, or achieve an acceptable level of noise suppression in revolvers that function under standard operating principles due to the looser gas seal between the barrel and the cylinder.