A practitioners guide for understanding the use of suppressors with subsonic ammunition as it relates to general shooting, and hunting small, medium and large game. This information is derived from 25 years of actual development and infield use, shooting subsonic ammunition of numerous calibers over a variety of applications. I do not consider myself an expert in the field, just a seasoned practitioner.
A suppressor is an excellent accessory for any firearm as it makes any type of ammunition hearing safe for the shooter, be it supersonic (above the speed of sound, >1135 fps at approx. 75 deg. F or 1050fps @ 0 deg. F) or subsonic ( below the speed of sound < 1135fps at approx 75 deg. F or 1050 fps @ 0 deg. F). The “speed of sound” varies with air density which changes with air temperature . A “ballistic crack”, as it is referred to in the shooting sports, is in reality a sonic boom that is generated when an object such as a bullet or a jet aircraft exceeds the speed of sound and as a result breaks the sound barrier. Shooting an unsuppressed firearm using supersonic ammunition the shooter does not fully comprehend how loud the ballistic crack is because it is effectively masked by the muzzle blast of the firearm. Shooting the same firearm with a suppressor and supersonic ammo the muzzle blast is vastly diminished and the full magnitude of the sonic boom is realized. Using high quality and very expensive decibel meters it has been proven that a ballistic crack generated by a centerfire rifle cartridge is nearly as loud as the unsuppressed muzzle blast of the firearm at 50 yards from the muzzle.
All that being said, shooting a firearm with a suppressor while using subsonic ammo (below the speed of sound) the ballistic crack is eliminated and the true effectiveness of a suppressor can be appreciated.
Let’s get down to the practical application of suppressed subsonic shooting. There are few if any downsides to using a suppressor on a firearm. However, the down-range performance of subsonic ammo often comes into question. Considering subsonic ammo is basically limited to a velocity of 1050 feet per second (so it is still subsonic @ 0 deg. F) how can you effectively use it for anything besides casual plinking? Well, as a point of reference, the original 45-70 black powder load used a 405 grain cast lead bullet moving at a velocity of 1200 feet per second, and managed to take every species of big game in North America until the advent of smokeless powder.
All that aside, the only way to improve the lethality of subsonic ammo is added projectile weight and projectile frontal area, (i.e. long flat nose/wide flat nose bullets). Muzzle energy energy is calculated as ‘projectile weight in grains’ multiplied by ‘velocity-squared’, then divided by ‘450240’ (a constant). So when velocity is capped at 1050 feet per second, increased bullet weight and diameter is all you have going for you. When you add weight to a bullet you also add length. Smaller diameter projectiles ( .30 cal and under) are constrained by overall length and therefore maximum weight due to barrel twist rates in commercially available firearms. If the projectile is too long it will not stabilize at subsonic velocities and a “baffle strike” can occur inside the suppressor and/or accuracy will be unacceptable. Larger diameter bullets (above .40 caliber) can grow substantially in weight without excessive increase in overall length and still maintain flight stability with most barrel twist rates available in modern production firearms.
Subsonic ammo is commercially available from .22 rimfire to 500 S&W magnum. So, if you are trying to decide which caliber is suitable for a particular hunting application I will relate to you my in field experience. Excluding head shots, .22 rimfire subsonic with an expanding hollow point is only effective on small game up to the size of a rock/wood chuck out to as much as a 100 yards. Even .22 through .30 cal centerfire subsonic ammunition with a non-expanding bullet & weights up to 240 grains is only consistently reliable at taking game weighing 60-80 pounds (with a well placed shot). Expanding subsonic bullets do exist, but penetration suffers on game with heavier skin & bone.
In the case of medium to large game animals such as deer, and elk, a projectile of .44 caliber or greater diameter, and weights of 400 to 600 grains with a large wide flat nose is required for one shot ethical kills. For these hunting applications bullet profile makes a major difference in terminal(down-range) performance. At subsonic velocities hydrostatic shock does not come into play like it does with high velocity ammunition, which is a major contributor to one shot drops on big game, with a well placed shot. Hydrostatic energy effectively “shocks” and temporarily shuts down an animal’s nervous system, evidenced by an animal dropping in it’s tracks. Really, blood loss and damage to vital internal organs is actually what leads to quick, clean kills. Using a large diameter flat nosed projectile (.44 cal and larger) at subsonic velocities is very effective at displacing tissue and driving deep enough through heavy hide, muscle and bone to cause rapid blood loss resulting in an ethical kill.
There are various firearm types that are compatible with suppressed fire using subsonic ammunition. Semi-automatic firearms are commonly used with suppressors, and subsonic as well as supersonic ammunition, such as AR-15 style rifles and pistol caliber carbines ranging from .22 to .50 caliber, which I own and use on a regular basis. One nuance that most people new to the sport are not aware of when shooting suppressed semi-auto firearms is ejection port noise. Due to the fact that a suppressor mounted on any firearm will cause gas pressure, in the barrel and action of a gun, to linger longer than a firearm without a suppressor attached. As a result, residual gas pressure will escape from the ejection port of a semi-automatic firearm when the bolt cycles. Depending on numerous factors this can lead to an excess of noise to the shooters ear which, at a minimum, is uncomfortable. If I am shooting a lot of subsonic ammunition in a semi-automatic rifle I will put an ear plug in my ear closest to the ejection port. It is not uncommon for other debris such as spent powder particles to escape the ejection port as well while shooting. Another consideration when shooting subsonic ammunition in a “gas gun” is cycling reliability. Direct blowback gas systems such as those used with pistol caliber firearms (ie 9mm, .40S&W, 10mm, 45ACP) are pretty forgiving when it comes to cycling reliability using subsonic ammo. Direct gas impingement systems as found in the typical AR-15 centerfire pistols and carbines (300 Blackout) often require some tuning (adding gas port regulators or changing buffer weights) to obtain reliable cycling using subsonic ammunition.
The other option for suppressed shooting is manually operated firearms, such as lever-action, pump-action, bolt-action, or single shot. The action remains fully closed and all gas pressure and particles escape through the muzzle and not back at the shooter. Typically these offer the quietest, most comfortable shooting experience, especially with subsonic ammunition. Adding a suppressor to any firearm significantly reduces recoil, whether shooting subsonic or supersonic ammo.
While this is not the last word out there regarding the use of suppressors and subsonic ammo, it is a sampling of the understanding gained from 25 years of personal experience developing subsonic ammunition, and shooting suppressed firearms, sending countless thousands of rounds downrange.
Hopefully this article shortens the learning curve for newcomers to this rapidly growing sector of the shooting sports.
Happy trails, Gary M.
