Muzzle blast

However, when the projectile exits the barrel, this functional seal is removed and the highly energetic bore gases are suddenly free to exit the muzzle and rapidly expand in the form of a supersonic shockwave (which can often be fast enough to momentarily overtake the projectile and affect its flight dynamics), thus creating the muzzle blast.

sound of the gunshot, and is important because it can cause significant hearing loss to surrounding personnel and also give away the gun's position.

The audible sound of a gun discharging, also known as the muzzle report or gunfire, may have two sources: the muzzle blast itself, which manifests as a loud and brief "pop" or "bang", and any sonic boom produced by a transonic or supersonic projectile, which manifest as a sharp whip-like crack that persists a bit longer.

The muzzle blast is by far the main component of a gunfire, due to the intensity of sound energy released and the proximity to the shooter and bystanders.

Muzzle blasts can easily exceed sound pressure levels of 140 decibels, which can rupture eardrums and cause permanent sensorineural hearing loss even with brief and infrequent exposure.

For small arms, suppressors help to reduce the muzzle report of firearms by providing a larger area for the propellant gas to expand, decelerate and cool before releasing sound energy into the surrounding.

[5] Other muzzle devices such as blast shields can also protect hearing by deflecting the pressure wave forward and away from the shooter and bystanders.

[7] It is thus important for the gun crew and any nearby friendly troops to stay clear of the potential directions of blast vectors, in order to avoid unnecessary collateral damages.

The overall recoil applied to the firearm is thus equal and opposite to the total forward momentum of not only the projectile, but also the ejected gas.

By using internal baffles, the gas is made to travel through a convoluted path before eventually released outside at the front of the suppressor, thus dissipating its energy over a larger area and a longer time.

This reduces both the intensity of the blast (thus lower loudness) and the recoil generated (as for the same impulse, force is inversely proportional to time).

These are commercially available, and have been installed by law enforcement agencies as remote sensors in many high-crime rate areas of urban centers.