AR15 Muzzle Brake/Flash Hider/Compensator Comparison, Part 2

Following up on the gargantuan first post of this comparison is a relatively short yet no less important portion. Especially to civilian shooters, the sound and blast of a muzzle device can be a huge turnoff. Yeah, that new brake keeps the muzzle on target, but if the noise rattles your friends every time you shoot the rifle, and other shooters on the firing line give you dirty looks and move away? Chagrin might give you second thoughts about your purchase.

For this portion of the test, a Brüel & Kjær 2209 Impulse Precision Sound Level Meter was used. Despite having been introduced in 1971 and looking quite like it could be an important quest item in Fallout 3, this is the device specified by the US Military and used by many silencer manufacturers to measure sound pressure level. The particular meter used for the test was provided by Rob Silvers of Advanced Armament Corp.

Since I forgot to take a better photo of the device, here's a cell phone pic.

Since I forgot to take a better photo of the device, here’s a cell phone pic.

As with the previous installment, scroll down to the charts if you’d just like to see the results.

Of course, all firearms are going to be loud. Even a silenced firearm with subsonic ammo makes noise. A rifle firing supersonic ammo without a silencer? Very, very loud. We are dealing with degrees of very loud here, but the difference between the loudest and quietest device (measured to the left of the muzzle) was approximately 8 decibels. Considering that a 10 decibel difference makes something sound twice as loud, these differences should not be considered entirely minor. If you would like to read some scientific papers regarding muzzle blast and gunshot acoustics, read this, this, or this.

But now, the charts.

First, using the military standard of 1 meter left of the muzzle and 1.6 meters above the ground, using Speer Gold Dot 64gr 5.56mm. These numbers represent the average of 10 shots.

spl1meter

After I had expended every round of .223 and 5.56 in my house, I used 5.45 to measure sound pressure levels at the shooter’s ear.

splear

To be entirely sure of these results, I actually shot them all twice, on four separate days.

As you can see, there is a pretty clear line between muzzle devices intended to reduce recoil and those intended to reduce flash.

29 comments

  • My basic takeaway from both of these posts? For once in history, Army Ordnance did a pretty dang good job in speccing out the A2 birdcage.

  • Given the trend represented by the graphs, would it be safe to postulate that the effectiveness of a particular recoil device has a direct and positive correlation to the db level observed perpendicular to bore ( and according to the Army, 1 meter left and 1.6 meters above ground )?

    Also, when these measurements were taken, was the rifle mechanically supported or did someone shoulder it. If the latter, does the above question correspond to a subjective opinion on recoil mitigation, based on the shooter’s experience ( if it was the same shooter for each device )?

    • 1. Not exactly
      2. It was shouldered. Objective methods were used for recoil control effectiveness

  • Way better than your previous attempts with crappy rented equipment.

  • o:
    You made a Fallout 3 reference! Squee!

    Also, yay, data! Science rules!

  • Thanks for being one of the very few sources of quality objective information in a sea of subjective testimonials.

    • … subjective testimonials with very limited experience.

      Go look at a forum, someone asks about a comparison between two competing devices. The huge majority of the replies basically say “I own one of those and like it, but I’ve never tried the other one”. Yeah, that’s helpful.

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  • Last year I used my 14.5″ barreled AR with an XTC for a javelina hunt. After firing three rounds at running javelina, my ears were ringing for about a month, and didn’t finally heal for three months. Seriously.

    • I am there right now. I was at a carbine class last september, and my muffs came loose from my ears just as another student fired a three round burst. it still sucks.

    • That stopping of the ringing wasn’t healing, it was hearing receptors dying for good. Hearing doesn’t heal; if you hear ringing, its damage that you don’t get back. How noticeable that is depends on a lot of variables, but any damage is still a loss of hearing.

  • SPL damage starts to occur = 120db
    SPL pain threshold = 130db

    Peltor Ultimate large muff attenuation = 30db

    The A2 is 157db at ear

    Even with the big Peltors you are at a resultant of 127db

    That 2X the SPL for causing hearing damage
    You are just under the pain threshold.

    That’s why I use both in-ear and large muffs.

    I don’t even want to think what I was being subjected to with a braked 308 in the adjacent lane with no panels in between last weekend.

    • You are confusing impulse noise with continuous noise.

      OSHA, for instance, limits exposure to impulse noise to 140 dB, while continuous noise is limited to 115 dB.

      • So when you’re on an indoor rifle range and surrounded by 15 other lanes going off with reverb everywhere I’ll make the supposition that that there isn’t much difference between that and continuous.

        I’m just encouraging people to take stock and evaluate what they are being subjected to and upgrade if necessary.

        • Anecdotal situations aside, you’re advocating doubling up on ear pro based on a faulty understanding of how hearing damage occurs.

          Do what you have to based on the situation, but your assertions about pain threshold and hearing damage are flat out wrong.

  • Brian Lepkowski

    Sounds stupid, but I took ear muffs with me (and put them on prior to pressing the trigger) on a coyote recently. I’m glad I did.
    Thanks for the data. Good stuff.

  • Brian Lepkowski

    *coyote hunt

  • Andrew, you’re mistaken about what 10 dB means. 2x sound pressure corresponds to a 3 dB increase, not 10. 10 db increase means 10x sound pressure.

    • Relooking at your link, I see you mean 10 db louder means subjectively “twice as loud.” Nonetheless, 3db still means 2x the energy hitting the ears.

  • Awesome review! Nice sound meter! My only suggestions is that decibels is a logarithmic unit, and the scale in the graphs is linear http://en.wikipedia.org/wiki/Logarithmic_unit#Logarithmic_unit, so the graphs should have a logarithmic scale on the axis for decibels.

  • Ok to make this a perfect series….

    devise some rig that measures XYZ forces at the muzzle and buttstock.

  • Minor note – at roughly +/- 3dB the actual sound pressure doubles or halves. A 10dB difference is a tenfold increase in peak pressure measured through the device.

    If anything, the differences are a LOT less minor – but from a couple feet back (16″ of barrel plus the 8.5″ or upper receiver, then the gap from cheekweld to ear), the apparent difference is going to be pretty close to an apparent twofold increase. So, along with all the other math nerds… just piling on.

    That said, looking forward to how you mathematically compare the impulse reduction to audible output relationship.

  • Greg in Allston

    Considering that the A2 FS is early 1960′s technology, the cost/benefit ratio is remarkably high.Kind of makes one long for the days of slide rules and draftsmen. Old school. Kink of like Apollo, the Blackbird and the Star Fighter.

  • I am glad that so much research has gone into muzzle brakes that may nearly double the already impressive bark of an AR15, while reducing its meager recoil by a relatively small percentage. #sarcasm

  • OK – so WHY is the Blackout so quiet?
    Also, is the STD roughly like a Levang Linear Compensator? Would these other types of compensators be quieter?

    Like you said, these are all going to be loud. But I’d like my rifle to be as quiet as legally possible (for me, the shooter) without spending tons of money on a suppressor.

  • Lithping Thamurai

    This is great – thanks so much for putting the time, effort, and money into this! Are you aware of, or could you create, a third section to this that explains HOW these devices do what they do, even if it is somewhat simplified? It looks to me like the majority of the devices out there have construction features that fit into a few main categories, with minor variations or even several combinations of those features in one device.

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