You have two different "sound cracks" when the bullet is fired. The explosion of the bullet out of the barrel and the round cutting through the air. Speed of sound is somewhere around 760 feet per second (depending on altitude/air density), resulting on the round breaking the sound barrier during flight if above that speed. 22 ammo comes in many different velocities (check the box). Subsonic ammo usually comes in velocities around 910 fps, thus allowing the blast crack and initial round through the air crack to be captured inside the suppressor with minimal residual sound. The lower the pressure of the round also can create cycle problems if not tuned properly.