Suppressors reduce the sound of shot by an average of about 30 dB(decibels), but they do nothing to reduce the sonic boom that a bullet makes as it flies through the air. The only practical way to eliminate the boom is to use subsonic ammo.
When a bullet travels through the air it creates two pressure waves – one at the tip of the projectile and one at the base. The faster the bullet flies the closer these pressure waves become. When the bullet reaches the speed of sound which is around 1125 fps. at sea level (depending on conditions), the two pressure waves combine into a single shock wave that produces a booming sound when the bullet passes by. The speed of sound becomes lower as one goes up in altitude and it increases as the temperature rises. Given the effects of atmospheric conditions on the speed of sound, it would be best to use ammo that keeps muzzle velocity down to around 1,000-1100 fps. if you want to ensure your shots stay subsonic. In the world of .22’s, ELEY carries ammo for all shooting disciplines – from their force line firing at speeds of 1250 fps or their contact line going subsonic at 1090 fps.
Before the turn of the 20th Century most handgun ammunition was subsonic and quite a few rifle loads lost enough velocity that they became subsonic by the time their bullets went 50 yards. But once magnum and +P handgun cartridges became popular and high-velocity supersonic rifle ammo became the norm for hunting, personal defense, law enforcement and military applications, sonic booms were the norm when shooting a broad number of different calibers.
Very little in life comes without a cost, and subsonic ammo does have its limitations. To start with, the maximum effective range of subsonic loads is usually limited to about 100 yds. That’s because subsonic ammo’s low velocity gives it a rainbow-like trajectory and makes it very susceptible to wind drift. Low velocity also seriously limits bullet energy because bullet energy increases as the square of the velocity. Unless specifically designed to expand at subsonic velocities, bullets travelling at subsonic speeds generally don’t have enough energy to expand well, and this limits their ability to transfer energy to the target. This has the potential to seriously limit stopping power. Therefore, the best way to make a subsonic bullet effective at neutralizing a target is through precise placement and deep penetration. The need for penetration is one reason why subsonic ammo is normally loaded with bullets that are heavy for their caliber.
But low energy doesn’t mean subsonic loads are useless for personal defense, competition or hunting. For example, during a Bullseye match it can be a lot more pleasant to shoot next to a person using a subsonic load than standing beside someone shooting a supersonic load. Even with ear protection the high-pitched crack of a sonic boom can be uncomfortable at such close quarters. In addition when using a properly designed bullet, subsonic ammo can be quite effective for hunting. Elmer Keith wrote about the great lethality of his 240 gr. Semi-wadcutter pistol bullets for hunting when they were moving at subsonic speeds. The sharp-shouldered slugs cut cleanly through animal hides and penetrated deeply. Today, activities that involve suppressors like overseas special forces engagements in urban areas, designated marksman operations for SWAT teams, competitions at covered shooting ranges and nuisance animal control hunts near dwellings or on the edges of communities all can be made quieter and more effective by using subsonic ammunition. That’s because the lack of a sonic boom makes it easier to concentrate during a Bullseye match, makes it less likely to give away the shooter’s position during combat and law enforcement engagements and helps prevent the shot from spooking targets during animal control operations.
Subsonic Ammunition Today
In today’s world, subsonic ammo is used for general shooting with calibers like the .45 ACP which always were subsonic, and it’s also used for specialized applications like shooting with suppressors to provide the maximum possible noise reduction. I use my Ruger SR22 that is equipped with a suppressor and Vortex Viper red dot for pest control as well as on the range. In conjunction with ELEY contact ammo, the sound is barely noticeable for wildlife, neighbors and myself. Supersonic ammunition is certainly better for long-range shooting, but nothing beats subsonic ammo and a good suppressor for tasks that require maximum noise reduction.