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Sound Suppressors: Hush, Puff, Shhh

By Paul Evancoe

Hollywood movies depict sound suppressors as “silencing” the report of a handgun or rifle to an almost inaudible “puff - puff’” sound. Most have no idea why or how suppressors work, why some designs work better than others, what role the choice of ammunition plays, or other critical operating dynamics that involve gun design and the unavoidable laws of physics.

Quite simply, a sound suppressor works by slowing the sonic (traveling above the speed of sound) swirling high velocity gases generated by the propellant’s burn to sub-sonic speeds as those gases leave the suppressor’s muzzle end. It took a modern scientific understanding of hydrodynamics to recognize that sound suppression pivoted upon two variables – reducing bullet velocity to less than the speed of sound (1,126 feet per second at sea level) and slowing the sonic high velocity gases generated by propellant combustion to sub-sonic velocity. This slowing of the swirling sonic velocity gases is scientifically described as disrupting the hydrodynamic axially rotating pipe flow – well; now you know.

The first condition for suppressing the firing sound (report) made by any firearm is to use sub-sonic ammunition (or porting the barrel itself to reduce the speed by reducing volume of propellant gases). Sub-sonic ammo leaves the muzzle below the speed of sound, with a velocity less than 1,126 feet per second. This is most often accomplished by “down-loading” the ammunition by either loading it with a slow burning sub-sonic propellant (smokeless powder), or using fast burning propellant ammunition in conjunction with a short-barreled gun thereby reducing propellant burn time which subsequently reduces bullet velocity.

The use of sonic rounds, especially in long guns like sniper rifles, that snap, crack and pop as they break the sound barrier in flight downrange is commonplace. The advantage of using a suppressor in conjunction with high velocity ammunition is that locating the shooter’s exact firing position is made difficult and it further reduces the requirement for ear protection by the shooter, allowing better situational awareness. Secondly, there is little loss of muzzle velocity or impact energy beyond that which would be experienced without the suppressor. Unless the gun has...


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