First-Round Pop

First-round pop is the audibly sharper report you hear on the opening shot through a cold suppressor, then notice fading on every shot after it. The accepted explanation is that the can holds a charge of fresh oxygen between strings of fire, and the hot, fuel-rich muzzle gas ignites that oxygen in a small secondary combustion, adding to the sound of the shot.

Once the first round has burned off the available oxygen and filled the can with inert gas, the following shots settle into the suppressor’s true sound signature. The effect shows up on any silencer, including an integral suppressor, and it is most obvious with a subsonic load where the muzzle blast, rather than the bullet’s flight, dominates what you hear. Like first-round pop, every muzzle device changes the acoustic character of a shot.