Suppressors and supersonic ammo

[Robinson]

I own a 300 BLK AR and I get that one of the driving things behind the cartridge is the use of subsonic ammunition in an AR-platform carbine. However, I am still on the fence about using subsonics in a defensive role. At this point there might be one or two ammo offerings out there that provide reliable expansion at subsonic velocities but choices are limited.

My question is around the combination of a suppressor and supersonic ammunition. Obviously there will be more noise with supersonics, but I have read conflicting information about just how much. Some people say just the sonic crack will register 140 dB, which is right at the OSHA-stated hearing safe threshold (and I don't consider that hearing safe, especially for people like me who have hearing damage).

I bought a SilencerCo Omega for my gun which was just recently approved by the ATF (yay!). On their web page, SilencerCo rates this suppressor at the following noise levels at the muzzle:

300 BLK -- 119.5 dB (my assumption is subsonic ammo)
5.56 -- 130.1 dB
.308 -- 133.9 dB

This suggests the noise from the bullet breaking the sound barrier may be less than some suggest. I plan to use earpro when shooting anyway, but am trying to gauge how damaging it might be if I ever have to shoot non-suppressed. I would expect suppressed 300 BLK from a 16" barrel to produce slightly less noise than 5.56 because all the powder will have burned up inside the barrel. It will still be loud because of going supersonic -- but perhaps in the upper 120 dB range? Or does the sonic crack take it well over that?

Do suppressor manufacturers noise level ratings take the sonic boom/crack into account?

Even target pullers at Camp Perry have to wear earpro when working the pits -- this makes me wonder how the sonic crack works. Does it occur just at the point the bullet breaks the sound barrier or does a supersonic projectile continue to make noise as it travels? I always assumed it just occurs once as the sound barrier is broken. I realize this part is mostly an academic question.

[joshs]

Going from 119.5 to 130-133 is a huge change. 10 dB is commonly considered to be about double the perceived sound and is several times greater power (which doubles about every 3 dB). This is due to dB being a logarithmic unit.

There are a lot of factors that control the perceived sound at the shooters ear. For example, some semi-autos do not suppress very well, so with the same suppressor/caliber in two different guns you can have a substantial difference at the shooter's ear even though they meter exactly the same in the common at the muzzle test. The same is true with a manually operated action vs. a semi-auto. Even if they meter exactly the same, there can be a substantial difference in perceived sound.

I perceive suppressed supersonic rifles as too loud to shoot without ear protection, but a suppressed subsonic Blackout doesn't even sound "loud."

[Matt O]

To add to Josh's point on subjectivity, as a lefty rifle shooter, a suppressed subsonic 300 BLk round (sample of gemtech subsonic loads) is slightly unpleasant sans ear pro.

[MistWolf]

The pressure wave from an object traveling at supersonic speeds is constant, just like the bow wave of a ship traveling through water. You will only hear the sonic crack when the wave passes over you.

You can hear the crack reflect off of objects as the bullet passes by. If a bullet were to be fired parallel to a row of telephone poles, for example, a listener would hear the sound of the sonic wave hit the poles and reflect. allowing the listener to track the path of the bullet by ear. If a sniper were to make such a shot, a listener could follow the line of the sound back to the shooter.

I don't know how many decibels the sonic crack produces. But the sound of each wave varies in tone and sound pressure according to many variables, such as velocity, size and shape of the object, humidity, pressure altitude and so on.

How much sound reduction a suppressor will give also is dependent on many variables and one of the most important, when comparing performance, is the location and type of the sensor. If the sensor is set a few feet from the muzzle at a right angle to the line of departure, the pressure wave from the sonic crack will be less than if the sensor was directly down range.

Although I find supersonic rounds out of a suppressor are still uncomfortably loud, it's much quieter than shooting without a suppressor

[Robinson]

The pressure wave from an object traveling at supersonic speeds is constant, just like the bow wave of a ship traveling through water. You will only hear the sonic crack when the wave passes over you.

Interesting. Actually I'm astonished and somewhat embarrassed that I didn't know that.

[DocGKR]

"However, I am still on the fence about using subsonics in a defensive role."

Subsonic ammo has a VERY narrow military niche and little reason for CONUS LE use. There is NO reason to be using subsonic ammo in a rifle intended for defensive use in CONUS--you just neuter the rifle and make it into a shoulder fired handgun. Might want to listen to the comments on subsonic rifle ammo here: https://www.youtube.com/watch?v=OLFEAtwNj0I

[Robinson]

DocGKR, thank you for posting that link. I listened to the first 40 minutes of it and will finish it when I have more time.

I don't think there is a good solution to the problem I am trying to solve. Which is: an effective defensive weapon easily suppressed so that even if not 100% hearing safe will greatly diminish hearing damage should it be used. Now back before I had serious hearing damage I was of the mind that should I ever need to fire a weapon without hearing protection it might cause damage to my hearing but I would still have most of my hearing intact and would be able to lead a normal life. But because I already have seriously damaged hearing and tinnitus that is challenging to live with, any gunfire I might be exposed to may affect me such that it becomes unbearable. I will make that sacrifice to protect those I care about, but probably not just for myself if it comes to it.

I selected an AR chambered in 300 BLK not because of subsonics necessarily, but since its powder will be completely burned before the bullet leaves the barrel it may be less loud than 5.56 -- especially suppressed. Enough to matter? I'm not sure. But it looks as if in order to have the performance of a rifle cartridge I need to accept that if I have to fire the weapon without hearing protection -- at all -- my hearing will be totally screwed and my tinnitus will be worse. Sobering.

Perhaps I would have been better off accepting the compromise of a handgun caliber and looked at 9mm sub guns instead of the AR. Or, I can accept things as they are and plan to always have earpro stationed near my defensive weapons and hope I have opportunity to put it on.

It's also possible I should start looking for a 5.56 barrel for my AR and switch over, if the 300 BLK won't be less ear damaging and is also less safe to fire in a residential neighborhood. I will say the 300 BLK seems quite a bit quieter when shooting at an indoor range than 5.56. When suppressed the difference is probably even greater.

[MistWolf]

Let me make a correction to my post- I wrote that the sonic crack will meter different when the sensor is 90° to the muzzle compared to playing the sensor down range. I meant to say the muzzle report will meter differently.

Robinson, while the report of a rifle firing supersonic ammo equipped with a suppressor is not entirely "hearing safe", it will be significantly less damaging to your hearing than a rifle, pistol or shotgun fired unsuppressed. A couple of shots may not have any permanent affects on your hearing at all. I have a 10.5 inch AR pistol for house defense and a suppressor for it, waiting to be released from quarantine

[MistWolf]

About the 300- it uses less powder than the 5.56 and the larger note means there is more volume per length, so pressure drops off sooner

[DocGKR]

Semi-auto pistol caliber carbines are an abortion that don't serve much purpose.

Put a suppressor on your .300 BLK, use standard supersonic 110 gr Barnes TTSX as your defensive load, keep a set of active hearing protectors (Sordin, Peltor, etc...) next to your rifle. That should work fine...