For this example use the Amphibia S as it is most notable since it is supposed to be quiet just the sound of the firing mechanism no actual firing sounds. In addition you could replicate this with a Sporter as well to verify the sound applies to all .22 ammo weapons.

1. Take weapon and load with ammo.
2. Have friend stand in front of you.
3. Aim just to the left or right of the person and fire.
4. Have friend back up and move forward various distances between magazines to note what all distances from you they hear it.
5. I suggest firing a large amount of rounds for testing 400 or more possibly 1000 as it didn't seem to always happen but more often than not. I imagine the times I didn't hear it was due to desynch or some calculation with position/distance etc.

I'll try to find the equipment to replicate this more and create a video possibly with a sporter or Trumpet as they are more readily available than a Amphibia S. I need to do additional testing with Water Bottle Supressors to see if you can still hear the crack as well with these on too.