Muzzle Brakes: Sound Test

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I thought about these muzzle brake tests for over a year before I started this field test. We all know one of the biggest downsides of a muzzle brake is how loud they are. If you’ve shot more than a couple of these, you know some are much louder than others. So I naturally wanted to quantify how loud each model was, but it turns out that is much more complex than it may seem. Steve Adelmann (one of my favorite gun writers) explains the issues involved in quantifying the sound signature of a firearm:

“When you compare decibel measurements from different sources, do so with no more confidence than you’d have of a politician keeping their word. Sound meters suitable for measuring firearm SPLs are expensive and hard to find. Since most of us can’t afford to hire an independent test lab, we’re left with our ears, published figures, and the scant independent studies made available to the public. Unfortunately many available figures result from sound meters designed for OSHA-type workplace measurements, which mischaracterize noise impulses from firearms. Beware the snake-oil salesmen on this point, the suppressor world is full of them, and the game they’re dealing has lethal implications for professionals.” – Steve Aldelmann, Shooting Illustrated

After reading statements like that from multiple sources, and talking to a few people who’d done this kind of sound testing … I was discouraged. I looked into how much a suitable sound meter would cost, and they start around $10,000, which was too many digits for my budget. So, I completely abandoned the idea of a sound test. Ultimately, I’d prefer to not publish anything on a topic, rather than publish something I think might be misleading.

But … one of the guys I called to be part of this test was Zak Smith at Thunder Beast Arms Corp (TBAC). They specialize in precision rifle suppressors, and offer models with Thread-Over-Muzzle-Brake (TOMB) mounts. I’ve always wondered how effective those kinds of muzzle brakes were compared to stand-alone brakes, so I asked if they wanted to include the TBAC 30 Caliber Compact Brake in my field test. After some conversation about all the tests I planned to run, Zak asked if he could bring down his new Ultra series of suppressors to test on my recoil system (view my post on the TBAC Ultra Suppressors). He was interested in gathering some hard data on their recoil reduction, and even plans to create a similar recoil test system to help with future product development. He was so excited about it, he drove several hours to come spend a long day gathering data at my range in Texas.

Of course, since Zak specializes in high-end suppressors … he owns a great sound meter. And now you’re thinking exactly what I was! So I asked Zak to throw in his sound meter when he headed down, and we spent a full morning measuring the sound signatures of all the different models. In return, I bought Zak a steak and measured the recoil reduction of all his new suppressors. But I can’t thank him enough for letting me borrow his nice sound meter, showing me the proper way to set up and run all the equipment, and helping me run through all the muzzle brakes. It’d have been a shame to not include anything on this aspect of muzzle brakes, and without his help … I wouldn’t have. So from me and all my readers: Zak, we really appreciate your help!

The Equipment & Setup

On this test, the equipment was pretty straight-forward. We used a calibrated, military-approved Bruel & Kjaer 2209 Impulse Precision Sound Level Meter equipped with a highly sensitive, precision microphone. This particular model sound meter is described by the American Shooting Journal as the “industry standard” for sound measurement.

We used the same tripods and other equipment that TBAC uses to test their suppressors. There seemed to be a lot of potential gotchas when measuring sound, so I was happy to have an experienced sound technician helping ensure we got it right. I normally encourage readers to run the same kind of field tests I do on their own rifles, but this test is an exception to that. As Steve Aldelmann said, this is a specialized science that requires advanced equipment and meticulous attention to detail. I’m obviously a detailed (borderline OCD) guy, but I couldn’t have done this without the help of a pro.

For these tests, we primarily used a 308 Win with a 20” barrel firing Federal Premium 168gr Sierra MatchKing Gold Medal factory ammo. A 308 Win seems to be what I see people typically use for sound measurements. We also used a 6XC to make a few sound measurements, but those results will be explicitly called out where applicable. These were all the same rifle and ammo combinations as we used in the recoil tests. We recorded the sound level for at least 3 shots with each muzzle brake, and calculated the average for each brake.

SilencerTalk.com offers a great overview of their testing method using the same equipment, along with a disclaimer that is good to keep in mind for my test as well:

While this data is captured in good faith and without bias under controlled circumstances, it is not always comparable to other environments or test equipment. An effort was made to have the data be reproducible and correlate with what a human observer would agree with, but your results may vary. This data must be interpreted with knowledge of how environmental factors such as temperature, humidity, and location effect the results. We do try to compare related products in the same session to make this data as comparable as possible.

All of this data was collected in the same session, and here are the environmental details for the morning we gathered the data: Temperature = 70°, Relative Humidity = 82%, Barometric Pressure = 26.72, Elevation = 3200 ft.

A Brief Primer in Sound

Before I dive into the sound data, let me explain some basics behind the science of sound:

“The decibel (dB) is the unit used to measure the intensity of a sound. The decibel scale is a little odd because the human ear is incredibly sensitive. Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound. That’s a big difference!” – HowStuffWorks.com

When it comes to sound, there are two key concepts we need to understand: Sound Intensity and Perceived Loudness.

Sound Intensity (Measured Sound Level)

Because the range of possible sounds is so huge, the decibel scale is different from most. Its logarithmic, which most of us aren’t familiar with. A difference of 10 dB means the sound is 10 times more intense, in terms of acoustic energy. Every 10 dB is an order of magnitude. If there is a 20 dB difference, that means its 100 times more powerful (10×10), and a difference of 30 dB would be 1,000 times more intense (10×10×10)! To help you understand the decibel scale, here are some common sounds along with some visualizations of their relative magnitude (graphic courtesy of  olegvolk.net)

Notice on the chart our baseline is normal speech at 60 dB (1x), then a dishwasher at 63 dB is twice as much (2x), and a vacuum cleaner at 70 dB is ten times as powerful (10x) as normal speech. So a difference of 3 dB can be thought of as twice as intense in terms of acoustic energy, and a difference of 10 dB is ten times as intense.

Perceived Loudness

But, that doesn’t mean 10 dB is 10 times louder. When we switch from talking about sound intensity to perceived loudness, we end up in a strange mix of science and psychology, because loudness is a subjective feeling and can be perceived differently by individuals. For that reason, we actually can’t measure perceived loudness directly. But psychoacousticians have done enough studies to know in general when the sound level increases by 10 dB a sound is perceived as twice as loud (source). Similarly, a 20 dB increase in the sound level is perceived as four times as loud by the normal human ear (2×2).

Clear as mud?! Here is a table showing how changes in measured sound level would apply to both measurements:

Sound Level Change	Perceived Loudness	Sound Intensity
+10 dB	2x (double)	10x
+6 dB	1.52x	4x
+3 dB	1.23x	2x (double)
0 db	1x	1x
-3 dB	0.82x	0.5x (half)
-6 dB	0.66x	0.25x
-10 dB	0.5x (half)	0.1x
-20 dB	0.25x	0.01x
-30 dB	0.13x	0.001x

A difference of 1 dB is the just-noticeable difference (JND) for the normal human ear (source), although that may be imperceptible by some people. A difference of 5 dB is clearly noticeable.

Both OSHA and MIL-STD-1474E require hearing protection if sound pressure levels are 140 dB or more (for “impulse” noises like gunfire). However, hearing loss can occur from sounds as low as 85 decibels with long or repeated exposure. Noise-induced hearing loss is cumulative and permanent. Ear protection typically reduces noise by 16-30 dB, which you can find by looking at their Noise Reduction Rating (NRR). For example, the popular Howard Leight ear muffs have an NRR of 22 dB. That may not get you below that 140 mark without “doubling-up” by wearing ear plugs in addition to the muffs. If you’re using a brake, please protect your ears, and pass that message on to your shooting buddies.

The Results

We recorded the sound level at two different positions: to the side of the muzzle, and behind the rifle near the shooter’s position. The sound meter was 1.6 meters above dirt/grass at both positions, in accordance with mil-spec standards.

The B&K 2209 sound meter has a max sound level of 170 dB. So the distances were picked to keep us under that max. Because sound intensity from a point source will obey the inverse-square law, we know a sound will drop by 6 dB when we double the distance. The total sound intensity at the source doesn’t change, but the energy is being spread over a larger area the farther you get from the source. “It’s like spreading a fixed amount of butter on two slices of bread. If one slice is larger than the other, the butter on it will be thinner,” explains NH Crowhurst.

So you can theoretically use the inverse-square law to scale the sound measurements to whatever distance you’re interested in. In fact, there are calculators designed to do just that. For example, mil-spec testing is typically done 1 meter to the side of the muzzle, but our sound meter was 1.524 meters to the side of the muzzle (to keep from pegging the 170 dB max). We measured the sound level of a bare muzzle to be 163 dB at 1.524 meters, so the inverse-square law predicts that to be a sound level of 167 dB at 1 meter … which is precisely what we measured for 3 bare muzzle shots we fired at that distance.

Without further ado, here is the data we recorded to the side of the 308 Win:

We also did a few measurements with the 6XC with a 24” barrel. For that rifle, we found the average sound level with a bare muzzle to be 163.4 dB, which is less than 1 dB difference from the 308 and therefore not a perceptible difference to the human ear. I also measured the Tubb Precision Muzzle Brake to the side of the 6XC, and it metered at 165.7 dB, which is 2.3 dB more intense than the bare muzzle.

Honestly, I had a case-head separation in my 6XC that knocked it out of commissioned for the rest of the day. So unfortunately, since I only had access to the sound meter that one day, I wasn’t able to meter the JEC Customs Recoil Reduction Muzzle Brake. I also wasn’t able to meter the Tubb Precision Muzzle Brake from behind the rifle. Sorry, guys!

Most sound measurements are taken from the side of the rifle, in accordance with the military specifications. But I also measured the sound levels from behind the rifle, closer to the shooter’s position. That is far more interesting to me, and seems more applicable for judging how loud a muzzle brake is. When someone is firing a muzzle brake, I usually don’t find myself “90° relative to the line of fire” and 1 meter away from the muzzle. Even if I did … I certainly wouldn’t still be there when they fired the second shot. 😉

Here are the average sound levels we metered behind the rifle, near the shooter’s position:

What’s interesting here, is the order of the muzzle brakes is much different than it was to the side of the muzzle. A big reason for that is because some of these brakes have angled baffles that direct more of the blast rearward. So when you meter those brakes from the side, you aren’t picking up all the pressure being sent back toward the shooter. But, when we metered the sound level from the second location, we come closer to capturing the effect a shooter or spotter would feel behind the rifle. That resulted in almost all the brakes with angled baffles metering louder than those with straight baffles.

When we measured the sound level from the side, there was only a difference of less than 2 dB from the quietest brake to the loudest. But from behind the rifle, that range jumped to 9 dB! That means from behind the rifle, there were some brakes that sounded about twice as loud as other muzzle brakes.

Now, remember that I didn’t have a chance to measure the 6mm brakes from behind the rifle, but when I metered the Tubb Precision Muzzle Brake from the side, it was almost identical to another 4-port brake with a 90° baffle design, the CSR Blast Tamer Muzzle Brake. So the Tubb brake may be similar to the Blast Tamer behind the rifle as well. Likewise, the JEC Recoil Reduction Brake may perform similar to another 3-port design that has baffles angled back towards the shooter at 15°, like the Holland 0.985” Radial Quick Discharge Muzzle Brake. That would actually put both of those brakes side-by-side at around 161 dB. That is just my rough estimates of where those brakes may have ended up based on the designs. Ultimately, I wish I could have metered them, but unfortunately, I only had access to the sound meter that one day and wasn’t able to get it done.

As I mentioned earlier, most of us aren’t used to working with logarithmic scales, and we may not realize how big of a difference there is between these numbers. So I translated those measured sound levels to the difference in perceived loudness compared to a bare muzzle, using a calculator intended for that purpose. The chart below shows how much louder each brake was compared to the bare muzzle.

If we just start at the top, you can see the OPS muzzle brake was the “quietest” of the batch. It says “+ 41%”, which means it’s still 41% louder than the same rifle without a brake (i.e. 1.41 times as loud). If you’ll remember, the OPS brake was also the worst performer when it came to recoil reduction … so I’m glad to see it wasn’t both ineffective and loud. 😉

Most brakes hovered around 100%, which means they sound twice as loud as the rifle with a bare muzzle.

Finally, we have some brakes that were more than twice as loud. We see some familiar names at the bottom of this chart: APA Fat B* and Little B* Brakes, the Alamo Four Star Muzzle Brake, the Holland Radial Quick Discharge Muzzle Brake, and the Impact Precision Muzzle Brake. If you’ll remember, those were some of the best performers when it came to recoil reduction.

There seems to be a correlation between how loud a brake is, and how well it reduces recoil. Most “quieter” brakes aren’t good at reducing recoil, and most of the brakes that are great at reducing recoil are very loud.

Like the other tests, I assigned a rating to each of the brakes in terms of how loud they were. My rating system worked like this: If a brake was only 20% louder than a bare muzzle, it would receive a full 10 rating. If a brake was 150% louder than the bare muzzle (which would be 2.5 times as loud), it would receive a rating of 0. The ratings were based on the measurements we made from behind the rifle.

Here are the loudness ratings, and I included the recoil reduction ratings for each brake as well in a semi-transparent color to show the side-by-side comparison.

The brakes are ordered by their loudness rating, but you can see most of the low recoil reduction ratings are towards the top and most of the high ones are towards the bottom. That is that correlation I was alluding to earlier. But you can also see that the order isn’t perfect, so there are some brakes that provide more recoil reduction compared to the increased loudness you have to endure … and there are some that go the other way (they’re unusually loud and don’t reduce recoil much).

A few noteworthy performers are the Badger Ordnance FTE Muzzle Brake and Seekins Precision ATC Muzzle Brake, which weren’t as loud as most of the brakes and they provided decent recoil reduction as well. Both the JP Recoil Eliminator and JP Compensator muzzle brakes also seemed to have good recoil reduction compared to how loud they are from the shooter’s position. The Center Shot Rifles Blast Tamer and Holland Radial Quick Discharge Muzzle Brake were good at recoil reduction, and not the worse in terms of loudness. And finally, the Alamo Four Star Cowl Induction Brake was one of the top performers in terms of recoil reduction, and it actually didn’t end up being the loudest.

Some of these brakes are clearly louder than others, but make no mistake … they’re all very loud. Here’s my analogy: If you got hit by a vehicle at 70 mph, it is going to hurt … regardless of whether it was a compact Kia or a big truck. Neither would be pleasant! Likewise, none of these brakes are pleasant. I’ve seen guys online looking for the “quietest muzzle brake,” and that is like looking for the tallest Leprechaun. You’ll likely be disappointed at the end of your hunt.

How Suppressors Compare

I’ve shown how suppressors compare in the recoil test and the ability to stay on target, so it’s only fair to show how they compare here. We all knew it would be a huge difference, but brace yourself. It’s a huge margin.

I tested all 3 of the new Ultra series of suppressors from Thunder Beast Arms Corp (TBAC), and they were all stellar at reducing sound. The Ultra 9 is their 9” suppressor, Ultra 7 is the 7”, and the Ultra 5 is the 5” model.

You can see there is a 43 dB difference from the quietest suppressor to the loudest muzzle brake. To the human ear that would likely sound 16 times quieter! Remember, psychoacousticians tell us 10 dB is usually perceived to the human ear as twice as loud. So a difference of 40 is 4 sets of 10, which is 4 doublings … 2×2×2×2 = 16.

If noise level is one of the big things you’re concerned about, the suppressor is clearly the way to go. If you’re trying to balance recoil reduction, ability to stay on target, noise level, and muzzle blast … you found the right field test! I’ll look at muzzle blast next … so stay tuned!

Other Post in this Series

This is just one of a whole series of posts related to this muzzle brake field test. Here are links to the others:

1. Field Test Overview & Line-Up: Overview of how the tests, what brakes were included, and which were caliber-specific.
2. Recoil Reduction Results: Let’s get right to the meat!
   1. Recoil Primer, Test Equipment & Rifles: Explains how I tested, and what equipment and rifles were used.
   2. Results for 6XC and 6.5 Creedmoor: Recoil results for the mid-sized 6mm and 6.5mm rifles.
   3. Results for 308 Win and 300 Norma Mag: Recoil results for the mid-sized 30 caliber and large magnum 300 rifles.
   4. Summary: Overview of recoil results from all rifles, and overall ratings of each muzzle brake.
3. Ability to Stay on Target: Lasers and high-speed cameras were used to objectively quantify how well each muzzle brake helps you stay on target through a shot.
4. Sound Test: A high-end sound meter was used to measure how loud each brake was to the side of the rifle and at the shooter’s position behind the rifle.
5. Muzzle Blast & Ground Signature: High-speed videos were shot of each brake to show the direction of the muzzle blast, and the impact that could have on the shooter.
6. Overall Summary: Putting all the results together in a summary that is easy to take in, and do side-by-side comparison, allowing you to draw your own conclusions on what muzzle brake is best for your situation.