Suppressor sound testing

Hi All,

We have started to do a few suppressor sound tests this week with the proper sound equipment (B&K 2209 with 4136 mic) using a factory Rem 700 308 sps, 24” with factory Winchester 150gr power point.

Our standard over barrel suppressor with four baffles gives an average sound reduction of 21.92db Additional baffles give 1 to 2db sound reduction each, we tested up to 9 baffles that gave us an average reduction of 31.20db

One of the test we thought would be fun was to try something we read in the book by Al Paulson: Suppressors ,history and performances volume one, on how to rig a suppressor test by using a liquid medium inside the suppressor to absorb some of the energy of the shot. (this reduced the first shot by nearly 8db more than a dry suppressor)

Video bellow.

https://www.youtube.com/watch?v=XkE8...ature=youtu.be

Why not make using a liquid medium a "feature". If it works, it works. Are there any detrimental effects to consider?

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Robbie Tiffen told me years ago that you could reduce the decibels by spraying CRC inside a suppressor but I never tried it.

Interesting. I wonder what effect if any it would have on accuracy.

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Would be interesting to see what other energy absorbing media can achieve - eg a silicon strip or washer on the face of each baffle, or even a suppressor design that was packed like a motorcycle muffler with fibrous material.

@DPT I thought the suppressor would have more reduction of db than that. It sure seems like it when using one. Why a 24" barrel?? not many people would be using a barrel this long. Great to see you doing the sound test:thumbsup:

The Decibel scale is not linear its logarithmic so 101 db is 10 times louder than 100db if my maths is right. So the unsupressed rifle is 130% louder. A pretty impressive sound reduction.

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Originally Posted by bigbear

@DPT I thought the suppressor would have more reduction of db than that. It sure seems like it when using one. Why a 24" barrel?? not many people would be using a barrel this long. Great to see you doing the sound test:thumbsup:

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@bigbear

every 3dB reduction is a halving of the sound energy.

Every 10dB reduction a ten fold reduction in sound intensity.

So a 21dB reduction via the DPT supressor is quite a significant reduction

Cheers
Pete

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Originally Posted by Marty Henry

The Decibel scale is not linear its logarithmic so 101 db is 10 times louder than 100db if my maths is right. So the unsupressed rifle is 130% louder. A pretty impressive sound reduction.

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And Sound level reduces by -6bB every time the distance doubles, so reduction at point of firing pays dividends at distance.

The first shot is loudest because of the oxygen in the suppressor, subsequent shots are quieter because the gas from the previous shot has displaced the oxygen. Similarly oil, CRC etc. achieves a similar result except the subsequent shots are quieter because of the firing gases mixed with oil fumes/smoke. That effect wears off after 4-5 shots and you get back to the normal repeat shot level. Sound absorbing materials, packing etc. reduce the effectiveness of any suppressor by reducing the volume needed to trap the gases. The most efficient units are filled with inert gas and sealed with thin plastic baffles. Such things are used by special forces but are only effective for the first couple of shots, and are not practical for normal use. 30 decibels of suppression is about the practical limit, and most suppressors are in the low to mid 20's which is fine for normal use, giving effective ear protection and confusing game.

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Originally Posted by gundoc

The first shot is loudest because of the oxygen in the suppressor, subsequent shots are quieter because the gas from the previous shot has displaced the oxygen. Similarly oil, CRC etc. achieves a similar result except the subsequent shots are quieter because of the firing gases mixed with oil fumes/smoke. That effect wears off after 4-5 shots and you get back to the normal repeat shot level. Sound absorbing materials, packing etc. reduce the effectiveness of any suppressor by reducing the volume needed to trap the gases. The most efficient units are filled with inert gas and sealed with thin plastic baffles. Such things are used by special forces but are only effective for the first couple of shots, and are not practical for normal use. 30 decibels of suppression is about the practical limit, and most suppressors are in the low to mid 20's which is fine for normal use, giving effective ear protection and confusing game.

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So if you sprayed a heap of argon say into your suppressor before firing you would have a better result?

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Originally Posted by Nibblet

So if you sprayed a heap of argon say into your suppressor before firing you would have a better result?

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Absolutely!

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Originally Posted by berg243

i can just picture you carting a bottle of argon up the hill with a tube from it into your suppressor to keep the noise level down.

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I've always considered carrying a can around for those people who can't take hints and keep banging on, spray some argon at them for sound insulation so I can't hear them anymore, now I have two reasons it's a real possibility [emoji6]

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I think covers are just to reduce noise if the can brushes against scrub. They would have a negative effect on the ability of the supressor to radiate heat, and as thats one way the sound is reduced would make the less effective after a couple of shots.

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Originally Posted by Nibblet

I've always considered carrying a can around for those people who can't take hints and keep banging on, spray some argon at them for sound insulation so I can't hear them anymore, now I have two reasons it's a real possibility [emoji6]

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Stick the hose down their throat and they'll be quiet forever

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Originally Posted by bigbear

@DPT I thought the suppressor would have more reduction of db than that. It sure seems like it when using one. Why a 24" barrel?? not many people would be using a barrel this long. Great to see you doing the sound test:thumbsup:

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That's what we had available in 308.
db figures are meaningless to most people as 20db what does that really mean? every 9db reduction in sound is perceived half the volume, so if you go from 100db to 109db it will sound twice as loud. Every time you double the energy you gain 3db, the 308 we shot un suppressed is 167.9db, if we were to get another 308 and shoot them side by side at the same time, the volume would only go up by 3db, you would need four 308s side by side to sound twice as loud as just one.

DPT

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Originally Posted by stretch

Why not make using a liquid medium a "feature". If it works, it works. Are there any detrimental effects to consider?

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I don't see it being very practical and could lead to issues if someone was to put too much oil in their suppressor and it drained into the barrel.

the dB scale was a result of alexander graham bell, the inventor of the telephone. a doubling of volume was a "bell" but it was a huge measurement so it was reduced to a deci-bell. in other words a 10th of a bell.
personally i think tesla was far more of a genius and edison was somewhat a wanker

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Originally Posted by berg243

would something like a felt washer glued to the baffles reduce noise or would it just reduce space thinking they could be sprayed with something like wd40 or crc and retain the liquid rather than it draining off into the lowest point of the suppressor .

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Probably but that would be a rather high maintenance suppressor

How about "at shooters ear" position?

Still over the 140dB "impulse hearing safe" or whatever level...? but good to see an NZ suppressor manufacturer actually doing some testing and releasing numbers.

Any plans to use the equipment for some more focussed R&D to bring it down?

The covers you see on suppressors are to reduce the heat mirage rising off the hot suppressor, especially important if varmint shooting.

The neoprene covers of most of the usual NZ brands are more for removing the distinctive metalic " ting" noises than reducing mirage.
If shooting varmints in great numbers those covers would melt pretty quickly.
As to the advanced "tactical " covers, they do reduce the heat mirage in front of the scope but would be cooking most aluminium cans fast. They are probably more suited to steel or titanium surppressors.

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Originally Posted by gimp

How about "at shooters ear" position?

Still over the 140dB "impulse hearing safe" or whatever level...? but good to see an NZ suppressor manufacturer actually doing some testing and releasing numbers.

Any plans to use the equipment for some more focussed R&D to bring it down?

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Yes, and we did just that the other day, had a few different baffle designs that we tried.

Is it possible to measure the volume of the sonic crack alone ? Maybe shooting over the mic at long range? Id be interested to see what the hypothetical levels might be with complete powder burn suppression.

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Originally Posted by berg243

has anyone tried extra baffles to see if different poi between more or less baffles.just asking as I have a set of 7mm baffles and wondered about adding them in for use on the range but removing them for hunting to keep my rifle nice and compact.

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Adding 2-3 baffles makes no difference to my 308 bushpig poi .

To sneeze: when I stand in the but for marking targets at my local range, I prefer to ear the gentle bark of a 223 or 6 mmbr bullet than the one of a fast 30 cal or 338!
So the size of the projectile and its moving speed has definitely an influence on the noise it produces when moving through the air.

To advman: I went from 6 baffles to 10 baffles on my 17" 308 once just to test and I had no change of the poi, but i can't guaranty that on rifles with longer barrel. There is only one way to really know for sure I guess.

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Originally Posted by Friwi

To sneeze: when I stand in the but for marking targets at my local range, I prefer to ear the gentle bark of a 223 or 6 mmbr bullet than the one of a fast 30 cal or 338!
So the size of the projectile and its moving speed has definitely an influence on the noise it produces when moving through the air.
.

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The noise level is largely proportional to the amount of powder burned, not what's coming out the barrel. A good comparison is a .223 v .22-250. That's why I got rid of the latter.

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Originally Posted by Friwi

To sneeze: when I stand in the but for marking targets at my local range, I prefer to ear the gentle bark of a 223 or 6 mmbr bullet than the one of a fast 30 cal or 338!
So the size of the projectile and its moving speed has definitely an influence on the noise it produces when moving through the air.
.

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Yes it it does, in this case DPT is using a 150gr from a 308. It would be interesting to know how much of the sound is from bullet vs powder for this particular test. That would in turn show us how much sound is able to be suppressed ( noise form powder burn from a 308 shooting a 150gr) and in turn what percentage of that the suppressor is achieving.

A bit of a belated thank you to Bert at ODL for his time and use of his testing gear, and his advice and experience on the use of liquid medium in sound suppression.

Darren
Does a reduced load i.e. Trailboss bring the sound down? We just use an extra baffle currently on the 223. Very quiet.

I summarised this from an article on supressors which I found interesting. Someone will no doubt put me right if bits are wrong. It certainly helped me understand how they work.
Approximately half the energy developed by the propellent when a cartridge is fired goes to make the bullet go forward the rest is shared between recoil, gas pressure energy, gas thermal energy and gas kinetic energy.
At exit, gas pressure in the barrel is around 10_15,000 psi with a temperature of about 1000 degrees c and its travelling at supersonic speed.
The energy in the gas is divided up roughly as heat 96% pressure 3.5% and kinetic the balance so getting rid of heat and pressure are key.
As the volume doubles the pressure halves so big volume in a supressor is good, also as the temperature halves the pressure drops a corresponding amount. Baffles increase the surface area cooling the gas more quickly and also kill off kinetic energy by creating turbulence.
The ultimate aim is to have bought the propellent gas speed down below the sound barrier and to have reduced the volume as much as possible by cooling so it escapes to atmosphere quietly leaving the sonic boom of the bullets flight as the only sound

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Originally Posted by R93

Robbie Tiffen told me years ago that you could reduce the decibels by spraying CRC inside a suppressor but I never tried it.

Interesting. I wonder what effect if any it would have on accuracy.

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grabbed one these today to throw in the range bag . . . certainly small enough to carry up the hill if it works . . cheers for the idea

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