Thread: Suppressor effectiveness - Think about this!

It may be speculative, but for the moment it is all I have seen. This is why I am trying to pin down some quantifiable numbers from real professionals like yourself who have the background necessary to understand the studies. I have approached this topic in forums around the world and not one individual will say XYZ is safe levels.

At least with that report, you can take a gunshot duration of around 20ms and say that some quantifiable number of shots in an 8hr day at a given dBA rating will be "safe". Without any other data to go on, what are those of us in shooting community to do? It may not be perfect but at least it is something. I would rather get a perfect set of data that a professional will stand behind but I have to think it either is too expensive to do the testing, or liability issues prevent anyone from attempting the study.

I have an accelerometer in my sound testing kit. I just haven't set it up yet. As soon as I catch up I will see if I can provide another set of data points with a different tool for comparison of brakes and suppressors. I know suppressors reduce the perceived recoil significantly. I am just not sure how much of the perception is due to the lowered sound. I am positive that a brake will redirect gas more efficiently in a shorter period of time.

My opinion is that the gas in a can will interact for a longer period of time and smooth the impulse that is felt. Sort of like slowing down from 100k can be done by hitting a wall in 1 second or stepping on the brakes for 10 seconds. The energy goes somewhere either way.

@ODL any plans for a thread on over barrel hunting can for bolt actions? Something light & short for a .260 perhaps

The guy who did the massive muzzle brake test on precision shooting measured the forces.
This link has a summary of results, scroll down for the suppressor. Not sure if he posts the actual graph for the suppressor anywhere though.
Muzzle Brakes: Recoil Results for 308 & 300 Magnum - PrecisionRifleBlog.com

Originally Posted by gimp

@ODL any plans for a thread on over barrel hunting can for bolt actions? Something light & short for a .260 perhaps

Yes, it is soon. I am finishing off some QD jobs with one starting production and the other is close. I set the A2 aside for now.

Short is relative. The Ratchet Lock is about 190 from the shoulder and is about 138 dBA at the muzzle which would put it around 130 at the ear for a bolt gun. I am not keen on shortening it up too much and losing the sound. That is why I am very interested in this thread though and some opinions of professionals in the hearing industry.

100mm ish forward seems like a good size.

Keen to see the QD available

ODL-

There is nothing I have read to make me support a particular dose/cumulative energy approach to specifying safe exposure to impulse noise.

The mechanism of damage is mechanical trauma to the Organ of Corti. This appears, according to the literature, to occur when the sound pressure level ( read- ~ peak acceleration) exceeds a threshold of 140SPL. I couldn't support any conclusion that this can be traded off by "shorter" peaks and/or a greater number of sub-threshold exposures. The 3dB integration rule that applies to (sub-115dB(A) ) continuous noise doesn't apply here as I read it.

Originally Posted by 6x47

ODL-

There is nothing I have read to make me support a particular dose/cumulative energy approach to specifying safe exposure to impulse noise.

So to see if I understand your comment: Above 140 and you get trauma to one organ. Continuous lower level noises 115 and lower induce trauma to a different organ. There is no body of evidence to support impulse noise guidelines in the range firearms will create impulses whether suppressed or with muffs in the 115 to 140 dBA range.

This is the problem. I really do appreciate your input into this. I also understand the threshold for making a comment as a scientist. But it leaves us with either the standard quoted or nothing. Until I can get a better guideline than the one quoted earlier, I will stick with that and err on the side of caution by extending the assumed duration of the shot. The peak value will only occur for a few microseconds and then there will be a variety of other lower level noises. To be cautious I will use the duration of sound above 115.

The primary effect of any permanent noise-induced hearing loss is depopulation of outer hair cells and this is particularly true of damage from continuous noise, eg chainsaws. High energy pressure spikes , eg gunfire, have a more diffuse effect on the whole Organ Of Corti. Outer hair cells are but one part of the Organ.

I think you need to forget 115dB(A) as it's not relevant to your area of concern. You need to be concerned with limiting peak exposure at any time to under 140SPL. In practice, this level is based on the integration time of traditional peak-hold instruments. I'm not aware of what time domain parameters current digitally-based instrumentation can alter.

My gear is peak hold analog B&K. I have looked into getting a digital interface and all the controversy about sampling rates and decided the cost is not justified. Especially from what you are implying that the primary concern is the peak number.

From the digital numbers that express the shot over a time graph, it looks like unsuppressed shots will be "peakier" with little duration to the event. Suppressors at best ranges have lower numbers with a softer curve compared to poorer suppressors which will provide more of a peak and faster drop off. The implied physics of the event seem to match that since the energy needs to go somewhere and the better you suppress, the longer the event will be. In fact, the better one suppresses, I would postulate that the damage mechanism would more accurately reflect the sustained noise and less the impulse. Your view on that would be appreciated, 6x47. Obviously if one is using muffs, plugs or both on non suppressed gun, it will be a pure impulse event with whatever reduction that is provided by the hearing protection worn (if any) and how well it fits.

Using table 1-2 as a guide, and three shot duration schedules, I made a table of number of shots that will keep a person inside the "guidelines". The peak duration is GUESSED at .002, .005 and .015 seconds based on some digital shot graphs on the internet for whatever that is worth. A person can determine how conservative they want to get and select the number they want to use. I guess this is kinda like birth control where the some matron comes out and says abstinence is the best and only proven method but I ain't gonna stop shooting.

Shot numbers in 8 hour day before exceeding limit based on three different shot duration peaks.
dB(A) - .002 - .005 - .015
140 - 45 - 18 - 6
139 - 55 - 22 - 7
138 - 70 - 28 - 9
137 - 90 - 36 - 12
136 - 120 - 48 - 16
135 - 145 - 58 - 19

I have measured unsuppressed centerfire rifles at 164 to 175 dB(A) so choose your ear protection accordingly if you are subtracting db's. Also keep in mind that these are numbers that are at the shooters ear. Semi auto rifles can vary a LOT at the ear based on how well the gas system is adjusted for the gun. For bolt guns, the muzzle number can usually have 8dB(A) subtracted on standard length (20"+) barrels for a rough "at the ear" number.

Yes, this post is asking to be heavily critiqued but we have to start somewhere.

Originally Posted by ODL

I have measured unsuppressed centerfire rifles at 164 to 175 dB(A) so choose your ear protection accordingly if you are subtracting db's.

What's an appropriate db reduction range to be looking at ear-pro wise?

I can see the basis for your belief that a broader peak (more total energy) is will do more damage but as I said, I'm unaware of data to support this.
More particularly, I doubt there is any evidence to support your integration rule. You'd be a brave man standing up in court trying to defend that

As for how much peak reduction a given personal hearing protection device will give, you will be making a bit of a guess there too. The reason is that attenuation is often non-linear, in some case very definitely. As an example, I occasionally have made for clients custom moulds into which I fit a non-linear filter. This particular filter (originally designed for the Aussie Army) provides very little attenuation at low inputs but becomes progressively more effective at higher inputs. The basis for this is feeding sound through a very small aperture - "turbulence" clips the peak, the louder it is.

Originally Posted by 6x47

More particularly, I doubt there is any evidence to support your integration rule. You'd be a brave man standing up in court trying to defend that

Well judge, I stand before you today charged with attempting to make some sense from a government study on hearing protection that was peer reviewed by over 30 PHD's and MD's. I did my best to quantify and offer mitigation suggestions based on the paper. I practically begged hearing professionals in the industry to critique and correct my conclusions. They said it was wrong but offered no other solution.

6x47, I understand where you are coming from. If the science is not fully conclusive, you can't stand behind an idea as a fact. You CAN offer suggestions based on theory, or best supported practice or other such disclaimer. Most of us shooters need to have an easy to follow guideline. Something like if your 300WM is 175 db you need a minimum grade 5 ear muff that fits properly to JUST get it to 140! So now you are maybe JUST at 140, how many shots will put you over the "safe daily noise threshold?

On the other point. I am not suggesting that the broader peak will have more energy since it is at a lower level. The energy of the shot is fixed by the uncorking pressure and the quantity of powder. I am really asking if the damage mechanism / damaged organ shifts more to the continuous realm versus the impulse realm. It is more of a question with the question directed at the quantity of shots causing damage with the two different mechanisms.

Your custom hearing molds have in effect, made a suppressor for the noise without having to deal with the bullet. This is a good thing. You must be able to now tell the shooter they have a custom fitted ear protection device that is good for X number of rounds at X dBA. What do you tell them and how do you determine the quantity?

Well, I guess my answer will have to be There is no definitive answer given the knowledge base available. You may well be right in your assumptions, who knows.

Have you seen that extensive NATO publication "Damage Risk from Impulse Noise"? If not, I can email it to you

Never underestimate a man's desire to fuss with a new gadget related to his hobby, or his need to justify it to those unfashionable enough to question it.

The amount of suppressed .223's I can beat the pants off ballistically with my standard length .222 nowadays is legion. I am going to call it a ".223 Express" now.

Cripes James - I started this thread to state the obvious in a subtle way, and now you've gone and kicked it round with hobnail boots!