Round impacts. Most people don’t know that each round has three sounds each, depending on your position.
- Muzzle sound from the gas bubble behind the round hitting the atmosphere.
- Supersonic crack if the shockwave is near you as the bullet goes by
- Impact thump/whack/bang, depending on what the bullet hits
There are also reflected waves from all of these sounds if they occur near large objects, like buildings.
The audio engineer should examine footage from recent combat in Afghanistan or Iraq.
Concur.
Analysis software used by the entertainment industry should be able to functionally decompose the wave form.
It would help if the location of the recording was established.
Distance of the sound wave from the weapon to the microphone, alignment, major reflective surfaces to form echos and pitch shift. Multiple echo harmonics involved.
Ricochets, impacts, splintered bullets, varying trajectories. All contribute to the perception of multiple shooters.