SSS.6.84 - Research Supplement: Taming the MK18, Part 3 - HUXWRX vs. Otter Creek Labs vs. Surefire (Members Only)
/The HUXWRX FLOW 556k, OSS HX-QD 556, Otter Creek Labs Polonium, and Surefire SOCOM556-RC2 with 3-Prong and WARCOMP, on the MK18 5.56x45mm AR15 with 10.3-in Barrel
Four silencers evaluated by PEW Science are included in this members-only Research Supplement to examine relative First Round Pop (FRP) and overall sound signature suppression performance characteristics. The four silencers were selected for their high average sound suppression performance at the muzzle or shooter’s ear on the standard PEW Science MK18 test host weapon system described in Public Research Supplement 6.51. All four silencers induce differing hearing damage risk to the shooter and bystanders on this weapon platform, on average, in accordance with their PEW Science Suppression Rating (Figure 1).
Part 1 of this series is located in Research Supplement 6.65 (Surefire vs. OSS).
Part 2 of this series is located in Research Supplement 6.72 (Surefire vs. CGS).
Suppression Rating Rankings can be found in Section 7 of the Standard.
Fig 1. PEW Science Suppression Rating Scale
The below five silencer configurations are a small subset of those available for the MK18 weapon system on the current market. The HUXWRX FLOW 556k, HX-QD 556, Otter Creek Labs Polonium, and the Surefire SOCOM556-RC2 represent significantly different technologies in the size and weight regime of interest that possess differing suppression performance to bystanders and at the shooter’s ear on the MK18 platform. The published Sound Signature Reviews of these five silencer configurations, with supersonic ammunition on the aforementioned platform, are linked below:
Bolt-action weapons allow for the elimination of variables to study pure sound signature suppression phenomena. Other than sound transmission through the weapon system itself, there is one primary source of overpressure to atmosphere (the bare muzzle or silencer endcap, if equipped). The MK18, however, is an automatic rifle. During the firing of an automatic or semiautomatic AR15 weapon system, a second pressure pulse originates from the ejection-port of the weapon and it occurs early enough in time such that its waves coalesce with that of the muzzle signature. It is not ejection port signature, alone, that dictates the signature measured at the shooter’s head position when firing an AR15.
Given the two origins of overpressure from a suppressed automatic weapon system such as the MK18, the holistic sound signature to which the operator and bystanders are subjected is dependent upon the so-called pure suppression performance of the silencer, as well as the silencer’s flow rate. The balancing of the two performance attributes; the relationship between the system’s muzzle Suppression Rating and ear Suppression Rating, dictates overall performance.
In addition to the balance of flow rate and suppression parameters, silencer mounting schemes may significantly influence the parameters themselves. Silencer mounts may inherently change flow rate, leak gas introducing a tertiary origin of overpressure, or both. This phenomenon was observed and quantified in PEW Science testing of Surefire silencers with the WARCOMP mount in both 7.62 mm and 5.56 mm cartridge regimes, with both bolt-action and automatic rifles.
The Otter Creek Labs Polonium and the Surefire SOCOM556-RC2 both exhibit a relatively higher muzzle Suppression Rating on the MK18 with a lower ear Suppression Rating. The HUXWRX FLOW 556k and HX-QD 556 exhibit a relatively lower muzzle Suppression Rating on the MK18, but a much higher ear Suppression Rating. The published Suppression Rating data with the MK18, to date, is shown in Figure 2.
Fig 2. Suppression Rating Comparisons Of various rifle silencers , Using PEW-SOFT 5.56x45mm Supersonic Test Data
The interaction of muzzle signature and ejection port signature, as they coalesce and impact the shooter’s ear, is complex. Nonetheless, the Suppression Rating allows for the quantification of hearing damage risk to the weapon operator due to the combined signature; the quantity of origins of overpressure is inconsequential. Only the holistic signature measured during the full gunshot time regime is required.
There are other flow dynamics and frequency components of silencer sound signatures that result in varying signature severity to the human inner ear for a given suppressed system. Furthermore, certain personnel may have preexisting hearing damage or other hearing sensitivity characteristics that differ from the 95th-percentile inner ear response with which the PEW Science Suppression Rating correlates. The impact of these differences on the human perception of silencer sound suppression performance has been quantified by PEW Science.
Section 6.84.1 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.
Section 6.84.2 provides detailed comparisons of the sound signatures measured at the muzzle.
Section 6.84.3 provides detailed comparisons of the sound signature measured at the shooter’s ear.
Section 6.84.4 presents some concluding thoughts.
This research supplement is intended to provide more information to PEW Science members with regard to specific sound signature characteristics of the tested configurations in the aforementioned reviews, and to help frame objective loudness comparisons between five silencer configurations exhibiting differing sound suppression performance on the MK18 weapon system. Both the FRP and average sound signature suppression regimes are examined. This supplement is part of ongoing PEW Science small arm weapon system sound signature research.
Note that the FLOW 556k is a new iteration of the HUXWRX (OSS) flow-through design; although it is the smallest silencer in this comparison, it results in competitive performance on this platform, relative to the other silencers shown. Like the previous HX-QD technology, the FLOW technology exhibits significant flow rate. This flow rate, and the mechanism of heat transfer which significantly drives the suppression mechanism in this technology, results in distinct signature features that manifest in human inner ear response.
PEW Science has determined that the FLOW technology shares extremely similar characteristics with that of the HX-QD technology, with some key differences. This article provides a first-look at the phenomena and is part of ongoing research.
6.84.1 Overall Sound Suppression Performance Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Otter Creek Labs Polonium is postulated to sound the quietest, with the HUXWRX FLOW 556k sounding the loudest, during the first shot.
Bystanders may interpret the signature from the HUXWRX silencers as “boomy,” relative to that from the other silencers.
On average, the Otter Creek Labs is again postulated to sound the quietest to bystanders, with the FLOW 556k being the loudest on average.
After FRP, the gap between the FLOW 556k and previous generation full-size HX-QD 556 is narrower to bystanders. Again, both silencers are postulated to generate significant low-frequency inner ear response to bystanders. Relatively high flow rate typically produces relatively high low-frequency inner ear response.
Shooter Perception:
To personnel firing the weapon, the SOCOM556-RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped Surefire silencer is the loudest to the shooter. During FRP, the HUXWRX silencers may sound “boomy” and generally louder, although they are quieter than the other silencer configurations during the first shot, to the shooter, except for the SOCOM556-RC2 with the 3-prong.
To personnel firing the weapon, on average, the FLOW 556k is the quietest silencer. However, the exacerbated low-frequency response of the HUXWRX silencers remains, due to flow rate, which may again result in the “boomy” perception to the shooter. The FLOW 556k exhibits enhanced suppression in a key area of human inner ear frequency response that differentiates it from the previous generation full-size HX-QD 556.
Even with the “boomy” signature characteristics, the HUXWRX FLOW 556k produces up to 85% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped SOCOM556-RC2 and over 36% less severe hearing damage potential to the shooter than the Polonium, on this platform, on average.
On average, the WARCOMP-equipped Surefire silencer still induces the highest hearing response to the shooter. The abnormal inner-ear response curve above 8,000 Hz is maintained over the entire shot sequence. This phenomenon is indicative of the persistent mount gas leak.
Relative FRP performance correlates strongly with overall composite Suppression Rating, in general. Normalized FRP and average suppression performance is compared in Figure 3. Despite the composite Suppression Rating correlation with FRP, there are occasional outliers in the detailed Suppression Rating correlation with FRP. Note that the maximum human inner ear damage potential of the silencer with the loudest measured signature in each regime is used in each respective normalization. This allows strict relative comparison of all the silencers shown.
The data should be viewed with the following muzzle behavior notes in mind:
During FRP, and on average, the HUXWRX FLOW 556k is the loudest silencer to bystanders with its muzzle Suppression Rating of 25.8.
The Otter Creek Labs Polonium is the quietest system at the muzzle, on average, and during FRP, with its muzzle Suppression Rating of 37.6
The gas leak from the WARCOMP mount lowers the Rating of the Surefire SOCOM556-RC2 to 29.2 at the muzzle. However, the Surefire silencer with the WARCOMP mount is still quieter in muzzle signature than the HUXWRX silencers in both FRP and average signature, at the muzzle.
At the Shooter’s Ear, the following notes apply:
During FRP, the Surefire silencer with the 3-prong is the quietest silencer at the shooter’s ear. However, on average, both HUXWRX silencers are quieter at the ear than the Surefire. This trend reversal is not discernable from the average at-ear Suppression Ratings (22.2, 27.5, and 31.8, respectively).
Regardless of FRP or average shot sequences, the Surefire silencer equipped with the WARCOMP mount is significantly louder at the shooter’s ear than the same silencer with the 3-prong flash hider and the other silencers shown. The average at-ear Suppression Rating of the SOCOM556-RC2 drops from 22.2 to 13.3 when changing from the 3-prong flash hider to the WARCOMP.
The Otter Creek Labs Polonium, while quieter at the shooter’s ear than the WARCOMP-equipped SOCOM556-RC2, is still significantly louder than the HUXWRX silencers at the shooter’s ear, on average.
As noted, the relative the Muzzle and Ear FRP and average measurements shown in Figure 3 are not comparable to one another. Muzzle numbers should be compared with muzzle, ear with ear, FRP with FRP, and average with average.
Fig 3. Normalized FRP and Average Performance Summary (Supersonic 5.56x45mm Automatic Rifle - MK18)
The data shown in Figure 3 is intended to present the likely human relative perception of FRP and average signature amplitude of the silencers to both bystanders and the shooter. It is important to note that the human inner ear responds differently to certain frequencies. On average, it is postulated that the relations in Figure 3 will directly correlate to human inner ear response. However, some users may have hearing sensitivity that is compromised or different than others in certain frequency ranges. Those phenomena are considered in this article.
The following subsections of this Research Supplement present in-depth comparisons of human inner-ear modeling response to the FRP and average sound signatures.
6.84.2 Comparisons of Muzzle Waveforms Measured in the Free Field
It is not always possible to determine relative, objective loudness from only the measured average peak sound pressure amplitude and measured peak sound pressure momentum transfer potential (impulse). Therefore, the Suppression Rating also considers physical ear response to measured sound signatures. The human inner ear responds to different sound pressure frequencies with varying sensitivity. Physically, these frequencies excite different regions of the basilar membrane within the cochlea. The human ear is typically most sensitive to sounds that excite the membrane near a frequency of 4,000 Hz. However, the ear may be exercised, and therefore damaged, at different physical regions. It is postulated that this inner ear response directly correlates to the perceived loudness of suppressed small arms.
PEW Science Research Note: As stated in previous Research Supplements, it is important not misconstrue the frequency-domain data in this Research Supplement with a simple frequency analysis (Fourier transform) of the time-domain overpressure waveforms presented in the reviews. The data shown in this research supplement is the output from analytical human inner ear modeling with the measured test data used as free-field overpressure loading input.
6.84.2.1 FRP Muzzle Comparisons
Figure 4 presents the results of an inner ear analysis performed using measured sound overpressure waveforms from the first shots in the referenced tests. The curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 4a shows the response on the vertical axis with a linear scale. Fig 4b and Fig 4c show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the silencers. To personnel located 1.0 m left of the weapon muzzle, the Otter Creek Labs Polonium is postulated to sound the quietest, with the HUXWRX FLOW 556k sounding the loudest, during the first shot.
Note that in the very low frequency response regime, both HUXWRX silencer signatures are significantly more intense than that of the other silencer. This phenomenon may result in bystanders interpreting the signature from the HUXWRX silencers as “boomy,” relative to that from the other silencers.
Fig 4a. Comparison of FRP Human Inner Ear Response - 5.56 at the Muzzle (Linear Scale)
Fig 4b. Comparison of FRP Low Frequency Human Inner Ear Response - 5.56 at the Muzzle (Log Scale)
Fig 4c. Comparison of FRP High Frequency Human Inner Ear Response - 5.56 at the Muzzle (Log Scale)
PEW Science Research Note: Bystanders with hearing loss above the 3,000 Hz range may perceive the sound delta between the two mounts used with the Surefire SOCOM556-RC2 to be less severe during FRP, than those with healthy ears. They also may not be as sensitive to the loudness differences between the two HUXWRX silencers, during the first shot.
6.84.2.2 Average Muzzle Comparisons
Figure 5 presents the average results of an inner ear analysis performed using measured sound overpressure waveforms from all shots in the referenced tests. Again, the curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 5a shows the response on the vertical axis with a linear scale. Fig 5b and Fig 5c again show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the silencers. To personnel located 1.0 m left of the weapon muzzle, the Otter Creek Labs is again postulated to sound the quietest on average, with the FLOW 556k being the loudest on average.
After FRP, the gap between the FLOW 556k and previous generation full-size HX-QD 556 is narrower. Again, both silencers are postulated to generate significant low-frequency inner ear response to bystanders. Relatively high flow rate typically produces relatively high low-frequency inner ear response.
The SOCOM556-RC2, on average, produces a higher low-frequency inner ear response to bystanders than does the Otter Creek Labs Polonium. Although the signature from the two silencers are somewhat similar to each other in severity to bystanders (approximately 7%), the SOCOM556-RC2 may seem louder to bystanders due to the high frequency response below approximately 2,000 Hz.
Fig 5a. Comparison of Average Human Inner Ear Response - 5.56 at the Muzzle (Linear Scale)
Fig 5b. Comparison of Average Low Frequency Human Inner Ear Response - 5.56 at the Muzzle (Log Scale)
Fig 5c. Comparison of Average High Frequency Human Inner Ear Response - 5.56 at the Muzzle (Log Scale)
6.84.3 Comparisons of Waveforms Measured near the Shooter’s Ear
The sound signatures measured at the ear during the tests of each silencer are significantly different than those measured at the weapon muzzle and this difference is not only shown in the average peak sound pressure and impulse measurements, but also with inner ear analysis.
6.84.3.1 FRP Ear Comparisons
Figure 6 presents an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from the first shots in all tests. Fig 6a shows the response on a linear vertical scale. Fig 6b and Fig 6c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively. To personnel firing the weapon, the SOCOM556-RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped Surefire silencer is the loudest to the shooter.
Below approximately 3,500 Hz, FLOW 556k excites the human inner ear less severely than all the silencers during the first shot until a cross-over point at 2,000 Hz in which the high flow rate of the flow-through technology exaggerates the inner ear response of the shooter. This indicates that during FRP, the HUXWRX silencers may sound “boomy” and generally louder, although they are quieter than the other silencer configurations during the first shot, to the shooter, except for the SOCOM556-RC2 with the 3-prong.
When the WARCOMP is used with the Surefire silencer, the signature is severe; the inner ear of the shooter during FRP is postulated to respond with greater severity than the other silencer configurations through the entire response range. Of particular note is the inner ear response above 6,000 Hz. The WARCOMP gas leak produces severe jetting that excites the ear of the shooter significantly even to 8,000 Hz and above. This inner ear response is the result of shock loading.
Regardless of response range, the WARCOMP-equipped Surefire silencer is postulated to be the loudest to the shooter during the first shot of the weapon. The Polonium is shown to sound harsh and likely louder than all silencers except for the WARCOM-equipped Surefire silencer to the shooter, during FRP.
Fig 6a. Comparison of FRP Human Inner Ear Response - 5.56 at the Ear (Linear Scale)
Fig 6b. Comparison of FRP Low Frequency Human Inner Ear Response - 5.56 at the Ear (Log Scale)
Fig 6c. Comparison of FRP High Frequency Human Inner Ear Response - 5.56 at the Ear (Log Scale)
PEW Science Research Note: As previously discussed in Research Supplement 6.65, the significantly higher inner-ear response with the WARCOMP-equipped Surefire silencer shows notably higher hearing damage risk to the shooter. The abnormal slope of the response curve above 8,000 Hz and the shock-load measured at the shooter’s ear displayed in the published Sound Signature Review highlight this severity. PEW Science urges caution when using the WARCOMP mount due to gas leakage and increased hearing damage risk.
During the first shot, almost all shooters will observe the HUXWRX silencers to be boomy and the 3-prong-equipped Surefire silencer to be quieter. Individual hearing sensitivity differing from 95th percentile human physiology may skew the postulated perception outcomes.
6.84.3.2 Average Ear Comparisons
Fig 7a. Comparison of Average Human Inner Ear Response - 5.56 at the Ear (Linear Scale)
Figure 7 presents the average results from an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from all the shots in the referenced tests. Fig 7a shows the response on a linear vertical scale. Fig 7b and Fig 7c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively.
To personnel firing the weapon, on average, the FLOW 556k is the quietest silencer. However, the exacerbated low-frequency response of the HUXWRX silencers remains, due to flow rate, which may again result in the “boomy” perception to the shooter. Nonetheless, the increased suppression in the 2,000 Hz to 4,000 Hz over the previous generation HX-QD technology is once again noted in the average signatures, like it was during the first shot.
Even with the “boomy” signature characteristics, the HUXWRX FLOW 556k produces up to 85% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped SOCOM556-RC2 and over 36% less severe hearing damage potential to the shooter than the Polonium, on this platform, on average.
On average, the WARCOM-equipped Surefire silencer still induces the highest hearing response to the shooter. The abnormal response curve above 8,000 Hz is maintained over the entire shot sequence. This phenomenon is indicative of the persistent mount gas leak.
Fig 7b. Comparison of Average Low Frequency Human Inner Ear Response - 5.56 at the Ear (Log Scale)
Fig 7c. Comparison of Average High Frequency Human Inner Ear Response - 5.56 at the Ear (Log Scale)
PEW Science Research Note: The response curves of the HUXWRX silencers and the 3-prong equipped SOCOM556-RC2 cross at approximately 1,800 Hz. This phenomenon, coupled with the higher response of the Surefire silencer above this frequency range, on average, results in the HUXWRX silencers most likely being perceived as “boomy” but still less harsh to the shooter.
6.84.4 Research Supplement Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Otter Creek Labs Polonium is postulated to sound the quietest, with the HUXWRX FLOW 556k sounding the loudest, during the first shot.
Bystanders may interpret the signature from the HUXWRX silencers as “boomy,” relative to that from the other silencers.
On average, the Otter Creek Labs is again postulated to sound the quietest to bystanders, with the FLOW 556k being the loudest on average.
After FRP, the gap between the FLOW 556k and previous generation full-size HX-QD 556 is narrower to bystanders. Again, both silencers are postulated to generate significant low-frequency inner ear response to bystanders. Relatively high flow rate typically produces relatively high low-frequency inner ear response.
Shooter Perception:
To personnel firing the weapon, the SOCOM556-RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped Surefire silencer is the loudest to the shooter. During FRP, the HUXWRX silencers may sound “boomy” and generally louder, although they are quieter than the other silencer configurations during the first shot, to the shooter, except for the SOCOM556-RC2 with the 3-prong.
To personnel firing the weapon, on average, the FLOW 556k is the quietest silencer. However, the exacerbated low-frequency response of the HUXWRX silencers remains, due to flow rate, which may again result in the “boomy” perception to the shooter. The FLOW 556k exhibits enhanced suppression in a key area of human inner ear frequency response that differentiates it from the previous generation full-size HX-QD 556.
Even with the “boomy” signature characteristics, the HUXWRX FLOW 556k produces up to 85% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped SOCOM556-RC2 and over 36% less severe hearing damage potential to the shooter than the Polonium, on this platform, on average.
On average, the WARCOMP-equipped Surefire silencer still induces the highest hearing response to the shooter. The abnormal inner-ear response curve above 8,000 Hz is maintained over the entire shot sequence. This phenomenon is indicative of the persistent mount gas leak.
This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.
