Home Forums Hunting & Shooting Hunter's Campfire dB test with brakes

Today, 12/13/14, I took the Savage with a Midway fluted 24" barrel chambered in .257 Weatherby to the range for recoil and dB testing. With no scope it weighs 6 lbs 5.5 oz. The load was Barnes TTSX 80 grain bullets pushed by 73.0 grains of IMR7828. The primer was a Federal 215 Magnum. The temperature was about 45 degrees. I fired three shots of each test. Instead of resetting the rifle back to the start after each shot I decided to fire each subsequent shot where it stopped to get a total distance for the three shots fired.

I used the new brake which has four .800" slots .100" apart that were cut with a 5/16" endmill angled 20 degrees to see if it was noticeably better than the one with four .750" slots .125" apart cut with a 1/4" endmill and angled 15 degrees.

I placed the smart phone with the dB app about where one's face would be on the stock when I squeezed the trigger. Being under a roof may have influenced the db readings. to protect what little hearing I have left I used ear plugs and ear muffs.

With no brake the total travel in the free recoil slide was 39 5/16". All three dB readings were 86.

With the slots facing forward the total for the three shots was 11 1/2". Two of the dB readings showed 86 while one was 87.

The professionally made shark gill brake allowed the rifle to move a total of 5 7/16". All three shots generated 88 dB.

With the slots facing rearward the rifle moved a total of 4 9/16". All three dB readings were 88.

Conclusion: Guns are loud! And rearward facing slots are way better than forward facing slots.

Fun and interesting experiments.

Interesting experiment.

If I were you, I wouldn't put too much faith in your SPL readings, for four reasons.

First, that microphone is most likely severely band-limited. Telephone audio is run through a fairly aggressive band-pass filter that strips it down to, if I remember correctly, 300Hz-3000Hz, because A) that's the region of maximum intelligibility for the human voice, and B) a narrower band means less data and more simultaneous conversations per network fiber. Anything outside the narrow band will be thrown away by the telephone network anyway, narrow-band microphones are cheaper, and smartphone manufacturers are all about price. A significant amount of the energy in the gunshot signature--maybe the majority of it--will be outside that band.

Second, it absolutely will not have a dynamic range capable of handling a nearby gunshot. Whatever its top SPL limit is, every sound louder than that will be clipped down to the limit. That's one of the reasons your numbers are all so close together.

Third, the software hasn't been calibrated against sound sources of known intensity--unless you've done that yourself, which I'll bet you haven't. (If you had a calibrated SPL meter to align your phone with, you would presumably have used that instead of your phone.)

Fourth, the software isn't going to be any good at measuring short impulse peaks like a gunshot. The metering program will run in a loop, where each time through it samples a few milliseconds of audio from the mic, runs it through a DSP algorithm to extract the average amplitude, and calculates SPL for that audio packet from the result. Your gunshot, or at least the peak impulse of it, will probably be overcome by the ambient noise in its packet of audio: if the gunshot peak is 2ms long and the packet is 50ms long, it'll be buried by a factor of 25.

Probably what you're actually measuring is the early reflections from the roof, the floor, the bench, the supporting posts, and so on. That's certainly not a completely useless measurement, but the impulse peak itself would be much more instructive.

If you feel like trying it again, you might move the phone back and back and back until you start seeing the dB readout drop away from the clip point--for example, move it back until you see your gunshot register 80dB. Then leave it there and make your test shots. Your absolute values will still not mean much, but you might get some use out of their relationship to each other--for example, maybe putting the brake on backwards quiets the gun by a certain amount, but putting it on forwards makes the gun louder by three times that amount.

An easy comparison as to why the measurements are suspect is with a loudspeaker.

87 dB is a typical number for what a speaker will do at a distance of one meter, given one watt of input. A gunshot is a lot louder than that.

Yea, your dB meter app isn't working. There's no way those numbers are accurate. I think you're facing the limitations of the smartphone, it's not a good tool for that.

You can get a real sound meter off of ebay or amazon for less than $30. If you want decent data on this experiment then that would be the way to go.

Crow hunter,



I didn't believe the dB numbers because I tested some of the sounds where I work. One machine gave a continuous reading of 90. There is no way a wide belt sander, even though it has five belts, is as loud as a gun shot. I posted the results because I had them.

Often I post that ignorance is my strong suite. The db app was new to me and a little fun. The "real sound meter off of ebay or amazon for less than $30" gets me in direction I never gave a thought. Thanks for the info. I will get one on the way and do this test again.

Now, gentlemen, let's have some input on your opinions about the no brake/ brake results.

I'm still most interested in the difference between ports facing forward vs backward. No doubt the ports facing back works better, but it looks to me like it still works very well facing forward, and if noise was significantly reduced by facing the ports forward, I'd gladly give up some recoil reduction. I've never had a ported rifle, but have shot a couple. Although they definitely worked very well, I'm not sure they would be worth it for me due to the ear-splitting blast. If that could be reduced considerably, it would make more sense for me. That said, I don't have any bench guns, if I did then it would probably make sense to have one on it.

You are definitely pushing the app beyond what it can do. At one meter, rifle reports are around 150 dB.

There are a couple of ways to compensate.

If you are shooting outdoors, you can simply put some distance between you and and the rifle. Or you can build a thick walled box that provides about 60-80 dB (that's a LOT) of attenuation, and put the phone in that.

xxclaro,

To brake or not to brake is not the question. Firing any firearm is damaging to hearing. You should get some quality hunting muffs and use them while hunting. When at the range use them in conjunction with ear plugs.

I will get off my soap box and encourage you with my most recent purchase. A dB meter is on the way.

denton,

I ordered a meter this morning. Next time I go to the range I will place it several feet behind the rifle and several feet to the sides for testing. The meter goes only to 130 so I will go far enough away trying to get a reading of maybe 125 with the brake facing rearward. Theoretically the forward facing slots and no brake should generate less dB at the same location. We will see. Or hear. Or at least read about it here.

You are correct, and I plan to get some decent hunting muffs this year. I suppose if I had those, the additional noise wouldn't be an issue anymore. Any recommendations on an affordable set?

Interesting results. The brake sure reduced recoil regardless of orientation. As xxclaro says, if the noise level turns out to significantly less facing forward, you are still getting about a 70% reduction in recoil, I'd take that route too.

If you've got 150 dB at 1 meter, then at 10 meters you should have 1/100th of the SPL. A factor of 100 is 20 dB. Rifles with muzzle brakes exceed the typical 150 dB level.

If your pickup mike is small, you might tape a pair of shooting muffs around it. Harbor Freight sells some 33 dB muffs for $10-16 depending on sales, though I would not rely too heavily on their published rating as a measurement standard.

Hope that helps some. Let us know what you find.