subsonic load question/supressor

[2wheelwander]

I have a suppressor on a SCAR and PCC 9mm. Obviously still get the crack from normal supersonic ammo.

Looking at loading subsonic ammo. And bear with me here, as I am new to this part of the game, if I am shooting subsonic ammo, that negates the need for a suppressor, does it not?

I get shooting subsonic with a can will be incredibly quiet. But is there a middle ground to eliminate the supersonic crack while shooting suppressed, yet still retain some energy downrange? Is this asking for the best of both worlds a futile pipe dream?

I guess in other words, how far can I push a load, suppressed, before the supersonic crack appears?

Also, I understand the differences in powders and burn rates, but how does this translate to subsonic loads? What type of powder is optimum? I see Trailboss seems to be popular for .308?

I do not own a Chronograph. But I'm guessing it past time I pony up for one.

Thanks for entertaining me. I know there is a lt going on here.

[Recycled bullet]

Use heavier bullets if you want to increase power level while still remaining below the sound barrier velocity.

For 9 mm you can use 147 grain bullets for 308 you could use 225 grain bullets Etc.

The suppressor is converting the energy stored in the plume of hot expanding gases into thermal energy that becomes exchanged into the body of the suppressor. The amount of time that it takes for this process to occur allows for the velocity and temperature of the gas to go down so it eliminates much of the muzzle blast.

You can certainly shoot supersonic ammo through a suppressor it just won't be as quiet as subsonics.

Keep in mind that certain hand loading recipes may or may not function your gun adjustments may need to be made.

Most of the fast pistol powders will make subsonics for 308. Most of them will not cycle a semi-auto 308 they're designed for bolt action guns.

Go look at hodgdons online Reloading Data then come back with more questions.

[44 AMP]

if I am shooting subsonic ammo, that negates the need for a suppressor, does it not?

No, not if you want things quiet. The standard for the speed of sound is about 1125fps (this varies quite a bit due to factors such as altitude and other things affecting air density).

You don't get the supersonic "crack" if you are subsonic, but you still get all the muzzle blast, so without a suppressor, a subsonic round is still quite loud.

Think of the standard GI .45acp or standard .38 Special loads at 850ish fps. These are subsonic, but are quite loud without some kind of suppressor.

Suppressors are a fairly accurate term, as they suppress, but do not eliminate all the muzzle blast.

"Silencer" gives the impression they do, but of course they don't. The name "Silencer" was a marketing name created by Hiram Maxim for his device. It has become a generic name for the product type, the way "Kleenex" is for tissues, but "silencers" never actually silenced the gun. Don't believe Hollywood sound effects. They aren't any more real than other "special effects" in movies or tv.

[Shadow9mm]

Subsonics does NOT negate the need for a suppressor. It does make it nicer to shoot imho, no Crack with the boom. But you will still leave your ears ringing if you try to shoot subsonics unsuppressed without hearing protection. Its not a pleasant experience I assure you.

There is no middle ground. You are either supersonic or subsonic.

To retain the most energy downrange switch to 147g bullets. Given all loads being subsonic, the heaviest bullet will have and retain the most energy.

One other trick, pick a powder that uses the least powder to get that 1050fps. Less powder means less gasses, less gas means the suppressor has to do less work, quieter load.

[Ike Clanton]

As far as powder burn rates goes. I learned the hard way that a slow burning powder does not work well for suppressor use. While making 45 acp ammo for my suppressed carbine I found VV N310 was dang near twice as quiet as CFE-P. The charge weight was much less too. I recommend a fast powder that requires the least amount of powder with a heavy bullet.

[Double Naught Spy]

Just curious, Ike, what decibel meter are you running? Years ago, I looked at several, but the ones that were rigorous and fast enough for gun shots were more than I could afford.

[2wheelwander]

This is all outstanding info gentlemen. Learned more than a few things already and cleared some misconceptions up. Thank you. Will be doing some research on the Hodgdon site.

[Ike Clanton]

I’m not using any metering equipment just using my ears haha. I suppose one could use an iPhone decibel app for a rough estimate as long as there is not much background noise they seem to work decent.

[Unclenick]

"Twice as quiet" by ear is about a 3:1 drop in muzzle blast in sound pressure level. The ear hears logarithmically, and for something to sound half as loud, a 10 decibel drop is required. The number of decibels of sound pressure change is 20 times the base 10 logarithm of the actual change in pressure.

Interestingly, air pressure and density affect loudness, as the change in pressure is what sound pressure level is all about, but they have little effect on sound speed. Sound speed relies mostly on air temperature. This is because temperature is the average kinetic energy in gas molecules, so the hotter the gas is, the faster its molecules move, and thus, the faster they can bump into each other like billiard balls to pass on the momentum in a sound pressure wave. Whether two molecules bump into each other over a short distance (dense air) or over a longer distance (thin air) makes only a slight difference to the speed of the pressure wave. Relative humidity makes a larger, but still small, difference because water vapor molecules occupy the same amount of space as other air molecules, but are less dense, so they move faster at a given kinetic energy level. A speed of sound calculator that includes both temperature and relative humidity is here. Try changing the air density, relative humidity, and temperature to see the effect on sound speed.

[44 AMP]

Sound speed relies mostly on air temperature.

In a way, it does, because temperature affects the density of air, and it is the density of the material that affects the speed of sound traveling through it.

The speed of sound in air (at standard values for temp and pressure) is approximately 1,125fps.

The speed of sound in water is 5,000fps.

The speed of sound in iron is approximately 5,120 METERS per second (17,968 fps)

And the speed of sound in space is essentially nonexistent (zero) because there is no material for sound to travel through, which is why they call it "space".

[Unclenick]

I know it's mind-blowing, but go to the calculator I linked to. Enter the ICAO standard atmosphere that ballistics calculators use as a reference value for BCs these days:

101.325 kPa air pressure,
15°C temperature,
0% RH.

You get a sound speed of 340.43 m/s (1116.896 ft/s).

Now, double the air pressure to 202.650 kPa to double air density without changing anything else:

You get a sound speed of 340.47 m/s (1117.028 ft/s).

So, doubling the air density increased the sound speed by 0.01175%

Finally, put the air pressure back to 101.325 kPa, and lower the temperature to 0°C, a change of not quite 2% in absolute temperature from 288.15 K to 273.15 K to use the international standard temperature.

You get a sound speed of 331.45 m/s (1086.45 ft/s).

So, a 200% change in air density changed the speed of sound 0.012%, while a mere 5.2% change in absolute temperature changed the speed of sound by 2.71%, which is very close (within 0.3%) to the square of 273.15/288.12 times the 15° sound speed, as would be proportional to the KE relationship to velocity. The slight difference (0.27%) is due to things getting squirrely down near absolute zero, I expect.

If you go to NASA's website, you'll find that their speed of sound calculator uses temperature as the sole argument because the other effects are too small to matter to most applications, because local atmospheric variations in temperature matter about as much.

Temperature is the average heat energy (the kinetic energy in the gas molecules) in molecules, so the square of the proportional change in absolute temperature would equal the change in velocity of those molecules. The velocity of the molecules is how fast they can propagate a sound pressure wave. This is the thing that tripped up one board member in the discussion of muzzle gas velocity. That combustion gas is much hotter than the outside atmosphere, so the speed of sound within it is much higher than the speed of sound in the atmosphere, so it is not limited to the speed of sound in air.