Subsonic vs. Supersonic Ammo: The Differences You Need To Know

So you just saw a box of ammo labeled “subsonic” and another one labeled “supersonic” – both claiming to be for the same firearm.

What do those words mean with regard to ammo? What makes one different from the other? You must understand these things before you can make the most effective use of your firearm.

Fortunately, it’s not all that complicated. Today, we’re discussing subsonic vs. supersonic ammo: their differences, their relative pros and cons, and which one is better for your needs. By the end of this article, you’ll know which type of ammo you should choose.

Let’s get after it.

Understanding the Speed of Sound and Its Effect on Ammunition

To understand the difference between subsonic and supersonic ammo, you must understand (A) the speed of sound and (B) how bullets are affected by it.

The speed at which sound waves travel depends on a few atmospheric variables (elevation, temperature, barometric pressure, humidity, etc.). For simplicity’s sake, it’s standard to assume the speed of sound equals 1,125 feet per second (ft/s; or 767 mph) at 68 °F. When an object exceeds the speed of sound (i.e., becomes supersonic), it breaks the sound barrier and issues a sharp cracking noise (sonic boom) as a result.

Ever been to an air show with fighter jets? Remember the awesome “ker-POW” as their engines fired off? Those were sonic booms.

What Is Supersonic Ammo?

Most modern ammo designs are supersonic by nature: i.e., loaded with bullets that exit the barrel at a velocity higher than 1,125 ft/s. Ignition of a supersonic cartridge is always accompanied by a distinctive “CRACK” – a literal sonic boom.

Supersonic bullets aren’t necessarily more powerful than subsonic alternatives (bullet weight also plays a significant role in striking energy), though they do tend to follow flatter trajectories to their targets. That facilitates aiming, as it allows the shooter to make less compensation for bullet drop (which becomes less pronounced when the bullet takes a relatively shorter amount of time to traverse a given distance).

What Is Subsonic Ammo?

Subsonic ammunition is designed to fire its projectiles at a velocity below the speed of sound (1,125 ft/s). It is typically loaded with heavier bullets than its supersonic counterparts (e.g., 300 BLK, which is supersonic at 150 grains and subsonic at 190).

Subsonic ammo’s performance is quieter than that of supersonic alternatives. It is unable to break the sound barrier, and therefore avoids producing a sonic boom on ignition.

I’ve always found subsonic ammo to have a softer report, generate less recoil, and deliver better long-distance accuracy. That third facet of performance is due to a quirk of physics. When a bullet’s velocity transitions from supersonic to subsonic, it undergoes what is known as “transonic destabilization.” This phenomenon causes the bullet to wander off of its intended trajectory — and is totally averted by a bullet that never becomes supersonic in the first place.

Subsonic vs. Supersonic Ammo

There are instances when subsonic ammo is better than supersonic ammo and vice versa. One is not inherently better than the other. To appreciate why, consider either type of cartridge’s potential benefits.

Subsonic Ammo Pros

• Reduced sound signature
• Optimal for suppressed shooting
• Improved long-range accuracy (bullet avoids picking up a wobble as a result of transonic destabilization)
• Noticeably lower recoil (if a cartridge is a subsonic variant of a normally supersonic type of ammunition, such as 30-30 Win)
• It won’t impact a shooter’s hearing as severely if fired in defense

Supersonic Ammo Pros

• Longer effective range
• Flatter trajectory (facilitates aiming by requiring less compensation for gravity; benefit is inconsequential at close range)
• Potentially higher striking energy and wounding potential

Either type of ammo also has its downsides, which can determine whether it is the worse choice for a given scenario.

Subsonic Ammo Cons

• May not reliably cycle certain semi-automatic firearms (22 LR being the prime example)
• Shorter effective range
• Potentially less powerful (although many rounds are subsonic by design, such as 45 ACP, a subsonic variant of a normally supersonic cartridge, such as 308 Win, will necessarily hit its target softer)
• Bullet exhibits more drop than a supersonic one at the same distance, which can make long-range shooting more challenging

Supersonic Ammo Cons

• Transonic destabilization causes the bullet to begin wobbling when its velocity slows to subsonic (which can take place at 50 yards or well past 1,000, depending on the cartridge type)
• Louder report (even with a suppressor)
• Potential for heavier recoil

Is Subsonic Ammo Weak?

Not necessarily. As mentioned earlier, several types of ammunition are subsonic by design. One wouldn’t call the 45 ACP, 45 Colt, or 190+ grain 300 BLK “weak” by any standard. They are all powerful enough to achieve their intended purposes. Subsonic variants of ammo that’s normally either sub- or supersonic aren’t necessarily weak, either. The 9mm is one example of a cartridge that’s commonly available in both subsonic and supersonic configurations. Its 115 grain bullets are supersonic, whereas its 147 grain projectiles are subsonic (+P ammo notwithstanding). Despite these differences, the two variants are approximately as powerful as one another.

You could objectively label subsonic ammo “anemic” if it’s significantly weaker than a supersonic alternative. This is common with cartridges that are usually supersonic by design. For example, Hornady Subsonic 30-30 has a power factor of 183.75 – less than half that of Hornady LEVERevolution.

Note that subsonic bullets are usually heavy (relative to whichever other bullets a cartridge is normally loaded with, at least). This bears on their terminal performance. Just as Newton's First Law of Motion holds that "an object in motion stays in motion,” so too does a heavier bullet tend to conserve relatively more striking energy downrange. Its higher momentum may also enable a heavyweight bullet to penetrate flesh more effectively.

Why Subsonic Ammo Pairs Well With Suppressors

Subsonic ammo is recommended (but not mandatory) for suppressors. A suppressor successfully muffles a supersonic cartridge’s report to some degree, although it cannot soften the sharp “crack” produced by a bullet breaking the sound barrier. By eliminating the supersonic crack altogether, subsonic ammo enables a suppressor to exhibit its fullest effect.

Now, I’m not the kind of guy who expects John Wick movies to be realistic. With that said, if two guys engaged in a suppressed gunfight at a crowded train station, bystanders would most certainly take note. Subsonic ammo isn’t “movie silent” when paired with a suppressor. No ammo is.

Examples of Supersonic Ammo

I’ve compiled a list providing examples of conventionally supersonic cartridges. Most modern ammo is supersonic, so this list could be much longer.

Supersonic Rifle Cartridges

• 223 Rem
• 5.56 NATO
• 243 Win
• 270 Win
• 30-06
• 308 Win
• 6.5 Creedmoor

Supersonic Handgun Cartridges

• 357 Mag
• 44 Mag
• 9mm (115 or 124 grains)
• 10mm

Examples of Subsonic Ammo

Subsonic Rifle Cartridges

• 300 BLK (190+ grains)
• 300 Whisper
• 338 Whisper

Subsonic Handgun Cartridges

• 380 ACP
• 40 S&W
• 9mm (147 grains)
• 45 ACP

Parting Shots: Subsonic vs. Supersonic Ammo

Now that you know the differences regarding subsonic vs. supersonic ammo, you’re better prepared to buy the right type of ammo.

For average hunters and target shooters, supersonic ammo should be the go-to option.

For suppressed shooting or those desiring a softer report (like during a home defense situation), subsonic ammo will perform better.

Whichever you decide to use, be sure to stock up at Ammo.com. We offer excellent prices, friendly customer service, and fast (but not quite supersonic) shipping!