SSS.6.152 - Research Supplement: Surefire RC2 vs. RC3 - What Changed? The Quietest 5.56 Rifle Silencers - Taming the MK18, Part 5 (Members Only)

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The Surefire SOCOM556-RC2 and RC3 with 3-Prong and WARCOMP, on the MK18 5.56x45mm AR15 with 10.3-in Barrel

Both Surefire SOCOM556-RC2 and RC3 systems are evaluated in this members-only Research Supplement to examine relative first round and overall sound signature suppression performance characteristics. These silencers were selected for comparison due to their similar mounting methods, with different design intents; the high flow rate (low back pressure) of the updated RC3 series, in contrast with the legacy RC2 design, results in different sound suppression performance at the muzzle and shooter’s ear on the standard PEW Science MK18 test host weapon system described in Public Research Supplement 6.51.

Commentary on the reason(s) for the design changes in the SOCOM556-RC3 from the SOCOM556-RC2 are provided below.  Following that commentary is technical discussion regarding the physical differences between the SOCOM556-RC2 and SOCOM556-RC3 rifle silencer systems that Surefire implemented in order to address the desired performance changes.  Portions of that technical discussion were provided in previously published article 6.151 evaluating the RC3 on the MK18.  Finally, the efficacy of the changes are discussed, followed by high fidelity signature analysis for PEW Science Members that highlights the changes in performance and resulting actionable detailed signature severity data for end users, to further complement the PEW Science Suppression Ratings, already presented.

Surefire RC2 vs. RC3 - Back to Basics - why the changes?

As tested, analyzed, studied, and presented in the PEW Science public research pedigree, the holistic sound signature of a suppressed weapon system; the overall pressure field, is dependent upon both the silencer and the host weapon.  The combination of silencer and host weapon also dictates other performance attributes such as flash signature, accuracy, “gas blowback,” and other interrelated parameters, all listed in the beginning of Section 7 of the Standard (Rankings).

As presented in PEW Science public research, it was determined that the Surefire SOCOM556-RC2 demonstrates extremely competitive signature suppression performance on the standard MK18 host weapon system (ref. 6.52).  Through the fielding of the system over a significant amount of time, in varying operational environments, and on a variety of weapon systems, end users equipped with silencers like the SOCOM556-RC2 have provided various constructive feedback on their performance.  Examples of the type of feedback received from end users, when fielding this type of silencer, include:

  1. The silencer may induce higher bolt carrier group velocity than the unsuppressed state, influencing reliability metrics.

  2. The silencer may induce earlier-time system unlock, resulting in ejection port blast being of higher amplitude and/or duration than desirable to the weapon operator and team members in close proximity to the operator.

  3. The silencer may, through a somewhat similar mechanism in (2), also induce a greater concentration of gas toxicity to the atmosphere immediately around the operator’s face, during firing.  This is referred to as gas blowback.

The above three potentially negative performance attributes of a system equipped with a rifle silencer are not unique to the Surefire SOCOM556-RC2. On the contrary, similar negative performance traits may be observed from weapon systems equipped with silencers such as the Otter Creek Labs Polonium (6.75), SilencerCo Saker (6.53), YHM Turbo T2 (6.98), and others. These types of silencers are often referred to as possessing “high back pressure.”  It is interesting to note that the Surefire SOCOM556-RC2, due its internal proximal porting arrays, exhibits a higher early-time flow rate than these silencers, and although is not considered to be “low back pressure” in the taxonomy, still possesses lower back pressure than those aforementioned silencers.  As a result, although now a legacy design, the RC2 series still may provide reduction in the above 3 negative performance traits over some systems and may be considered more advanced.  When combined with its high first-round signature suppression performance, and notable consistency on short-barrel weapons, the SOCOM556-RC2 is still considered to be a higher performing system than more simple rifle silencer designs.

Nonetheless, despite the relatively advanced performance of the Surefire SOCOM556-RC2, end user requirements discussed above are addressed in a gross system design change.  The SOCOM556-RC3 is Surefire’s first update to the RC2 rifle silencer series.  Technical design differences are discussed below.

Surefire RC2 vs. RC3 - Design Differences - What Changed?

In previous generations of Surefire silencers, combustion gasses expanding into the blast chamber from the muzzle orifice are vented into an annular cavity through proximal blast chamber port arrays.  As stagnation of the under-expanded gas propagation is somewhat delayed in time due to that venting mechanism, the RC2 series, for example, exhibits lower overall back pressure than traditional rifle silencer designs (as discussed above).  The reduction of additive blast chamber impulse, resulting in a somewhat lower alpha parameter, coupled with limited baffle porting to control the external rate of gas momentum accumulation (Omega, 6.40), defines the holistic signature characteristics of the RC2 silencer design pedigree.

In the RC3 series, a similar design is employed.  However, instead of delaying pressure stagnation within an early finite time window, the annular vent paths of the RC3, fed by both the blast chamber and baffle vents, are directly and expediently vented to atmosphere though distal ports circumferential to the primary bore end cap orifice. This distal vent array is the final stage of a secondary passive attenuator; a similar component present in silencers from CGS Group, SIG, SilencerCo, and others.  The stages and their transitions are  considerably less advanced than others, such as those from HUXWRX or stages of certain technologies from Combat Application Technologies (CAT).  For a discussion of various back pressure-reducing designs present in silencers with high early time or late time flow rates (or both), see PEW Science Member Research Supplement 6.124.  That supplement provides an overview summary of Flow-Through, Total Signature Reduction, SURGE BYPASS, and Forward Flux technologies.  Specifically, that supplement contains high fidelity response analysis in the combustion regime generated from the use of subsonic ammunition; a regime in which the efficacy of the aforementioned technologies also differs.

All silencer technologies that are intended to increase early-time, late-time, or gross flow rate, and balance signature suppression performance, possesses compromises. Due to the nature of the weapon systems, their size envelopes, and current technological limitations, it is reasonable that these compromises exist, to include more severe signature production.  However, not all silencer technologies are created equal with regard to their ability to minimize the compromises and maximize performance efficacy on certain systems.  The PEW Science laboratory continues to perform research, both public and private, to characterize the limits of such performance.  The performance of the Surefire SOCOM556-RC3, and the comparison to that of the legacy SOCOM556-RC2, provides a case study of the changes made to a design to advance and expand a performance envelope while simultaneously minimizing the traditional signature reduction compromise noted above.  To that end, the following discussion addresses the real and actionable performance changes resulting from the RC3 design.

Surefire RC2 vs. RC3 - Performance Variation - Why do The Changes Matter?

The performance of a passive blast attenuator is a function of various parameters.  In a rifle silencer, traditional attenuator designs must be modified to address early-time shock reflections that develop in close proximity to the muzzle orifice if they are to possess secondary high flow stages with holistic back pressure reducing benefits.  The design must minimize early time impulse accumulation near the orifice (alpha), while managing transition to the the secondary stage consistently (Omega control).  In the Surefire SOCOM556-RC3, this is somewhat accomplished through angle of incidence on the concave face of the blast baffle and tuned with aft vent array location.  After the first gas expansion stage is complete, the RC3 reverts to a passive vent mechanism that is similar to that implemented in vented CGS Hyperion technology, with which it shares some design similarities.  The RC3 baffle flow is transmitted to the annulus at multiple porting stages.  The annulus is directly vented to atmosphere at the distal end, at which both the annular venting and primary nozzle geometries are tuned to manage shock propagation and flash reduction.  The practical consequence of the RC3 vent design, and its second stage, is two-fold:

  1. The design may possess extreme sensitivity to initial conditions (blast chamber muzzle orifice jet input dynamics).

  2. If (1) is not properly tuned, unintended consequences may result, to include uncontrolled distal flow rate.

The two consequences above are of importance to the end-user, as (1) may dictate muzzle device preference and (2) may significantly influence both sound and flash suppression.  These consequences occur despite distal orifice geometry intended to shape exit jet dynamics.  

The design changes in the RC3 that allow the silencer to exhibit a higher gross flow rate to mitigate the negative aforementioned performance feedback, while simultaneously minimizing negative performance compromise, do have efficacy.  However, as tested and observed, there are limits to the performance efficacy and the end result of the silencer evaluation on the standard MK18 indicates that there are other systems that may potentially provide superior overall performance for the platform.  Furthermore, the design changes in the RC3 do result in a performance state that is objectively more sensitive to mount choice than observed with the RC2.  Users should note that it is not only the ported WARCOMP blast load leak phenomenology that may decrease performance of the RC3; it is also the geometry of the flash hider tines, themselves.  This independence of mount leak on system performance change, and dependence on internal expansion (blast) chamber geometry for normalizing distal flow, was presented and examined in article 6.151.

SUREFIRE RC2 VS. RC3 - actionable data and analysis for the end user

Four configurations of Surefire rifle silencers are examined in this supplement. They include the RC2 and the RC3, both with the SOCOM 3-Prong flash hider mount and the closed-tine WARCOMP flash hider mount.  The published Sound Signature Reviews of these four silencer configurations, with supersonic ammunition on the aforementioned platform, are linked below:

All four configurations induce different blast and shock dynamics, different flash signature, and different hearing damage risk to the shooter and bystanders on this weapon platform, on average, in accordance with their PEW Science Suppression Rating (Figure 1).

Similar in-depth response evaluations have been presented by PEW Science for the MK18. This article is Part 5.

Fig 1. PEW Science Suppression Rating Scale

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 early-time shock environment and overall flow rate. The balancing of these performance attributes; the relationship between the system’s muzzle Suppression Rating and ear Suppression Rating, dictates overall performance.

In addition to the balance of shock dynamics, 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  SOCOM556-RC3 testing and analysis further indicated a change in gas dynamics due to mount system, independent of gas leak.

The Surefire SOCOM556-RC3 and the Surefire SOCOM556-RC2 both exhibit a relatively higher muzzle Suppression Rating on the MK18 with a lower ear Suppression Rating.  In the case of the RC2, the design is more restrictive, and the operator Suppression Rating is reduced due to ejection port blast coalescence.  In the case of the RC3, the design exhibits a higher flow rate, but the method by which it is achieved results in muzzle blast coalescence lowering the operator Suppression Rating to similar of that generated by the RC2 on the same system.  When changing to closed-tine WARCOMP mounts, both the systems have reduced levels of protection to the operator and bystanders, but through different mechanisms.  The published Suppression Rating data with the MK18, to date, is shown in Figure 2.  Both RC2 and RC3 systems are highlighted in red.

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 6.152.1 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.

  • Section 6.152.2 provides detailed comparisons of the sound signatures measured at the muzzle.

  • Section 6.152.3 provides detailed comparisons of the sound signature measured at the shooter’s ear.

  • Section 6.152.4 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 of the Surefire SOCOM556-RC2 and SOCOM556-RC3, and to help frame objective loudness comparisons between the four silencer configurations exhibiting differing sound suppression performance on the MK18 weapon system. Both the FRP and average sound signature suppression regimes are examined. Specific signature features occurring to do design changes are apparent and noted.  This supplement is part of ongoing PEW Science small arm weapon system sound signature research.

In article 6.151 examining the SOCOM556-RC3, there is a Detailed Mount Performance Comparison Case Study presented in Section 6.151.3. The reader is encouraged to review that case study in addition to the below analysis, for a full understanding of the differences between the RC2 and RC3 system on the MK18, and how mount changes can specifically influence RC3 performance.

This article provides a first-look at a performance comparison of the two technologies, in similar fashion to previous PEW Science Research Supplements.  Thank you for your support.

6.152.1 Overall Sound Suppression Performance Summary

The RC3 design changes were implemented to address the restrictive flow rate of the RC2.  When implementing the design changes, Surefire addressed the propensity for more severe signature propagation and first-round flash with particular geometric features.  In the final RC3 product, the performance of the system achieves several design goals while compromising some performance attributes of the legacy RC2 system, an introducing some performance challenges.  There may exist other systems with high flow rate that outperform the RC3 with less compromise on the same weapon system.  PEW Science research to compare the performance of these systems, in context, is ongoing.  

The following are detailed signature analysis conclusions for both bystanders and operators using the RC3 and RC2 on a MK18 weapon system, in the free field:

Bystander Perception:

To personnel located 1.0 m left of the weapon muzzle, the RC2 with the 3-Prong flash hider is postulated to sound the quietest, with the RC3 with the closed-tine WARCOMP flash hider sounding the loudest, during the first shot.

Bystanders may interpret the first-round signature from the 3-Prong mounted RC3 silencer as “boomy,” relative to that from the other silencer configurations, and potentially even more “boomy” than a WARCOMP-equipped RC3.  This is likely due to the WARCOMP leak coalescence exacerbating higher frequency response due to the fast rise-time of the pressure release blast load shock compared to the high flow rate of the typical distal jet from the 3-Prong RC3 system.

The boominess of the WARCOMP-equipped RC2 over that of the 3-Prong mounted RC2 is due only to a mount leak, and illustrates how such a blast load leak influences severity in the absence of high distal flow.  The RC3’s boomy nature is similar to that of a high-flow silencer like a HUXWRX FLOW system.  So-called boomy signatures from an RC2 are only possible through blast load leak compromise.

Bystanders with hearing loss above the 3,000 Hz range may perceive the sound delta between the two mounts used with the RC3 to be less severe during FRP, than those with healthy ears. As noted above, a WARCOMP mounted RC2 has an FRP signature that may induce a more “boomy” impression to bystanders, but not as “boomy” as an RC3 silencer, regardless of mount used with the RC3, due to the higher predicted ear response in the lower frequencies. This phenomenon with the RC3 is not isolated to FRP.

On average, the RC2 with the 3-Prong is again postulated to sound the quietest, with the WARCOMP-equipped RC3 again being the loudest.

After FRP, the gap between the WARCOMP-equipped RC2 and the 3-Prong-equipped RC3 is narrower. Again, both silencer configurations 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 RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped RC2 silencer is the loudest to the shooter, not the WARCOMP-equipped RC3.

Below approximately 2,000 Hz, the WARCOMP-equipped RC2 excites the human inner ear less severely than the WARCOMP-equipped RC3.  This is due to higher distal flow rate from the RC3.  However, ejection port blast coalescence from the RC2 system results in more severe response above 2,000 Hz, and throughout the entire range.  This indicates that during FRP, the WARCOMP-equipped RC3 may sound boomy, but the WARCOMP-equipped RC2 will sound boomy and more harsh to most operators.

During FRP, the 3-prong-mounted RC2 is predicted to be the least severe to the operator. This is due to the silencer’s superior first-round signature suppression performance. The first-round signature of the 3-prong-mounted RC3 is more severe, both in low frequency inner ear response (below ~2,500 Hz) and in overall uncontrolled distal flow rate, resulting in the peak response shown near the 4,500 Hz region and above. 

The 3-Prong-mounted RC3 also induces exaggerated inner ear response above 4,000 Hz, but this is due to high uncontrolled distal flow rate.  This is an unusual performance attribute of the RC3.  The RC3 does not provide the first-round signature suppression capabilities of the RC2, to bystanders nor to the shooter.  It is unable to provide this to the shooter, despite its higher flow rate.  Uncontrolled distal flow is the cause of this performance detriment.

The lower ejection port blast and different mount leak dynamics result in less high frequency severity with an RC3.  During the first shot, almost all shooters will observe all the Surefire silencer configurations to be boomy, other than the 3-Prong-equipped RC2, on this weapon system.

To personnel firing the weapon, on average, the 3-Prong-equipped RC3 is the quietest silencer. However, the exacerbated low-frequency response of the two RC3 silencers configurations remain, due to flow rate, which may again result in the “boomy” perception to the shooter. This analysis further supports the conclusion that low first-round shot suppression of the RC3 is a significant performance factor.

Even with the “boomy” signature characteristics, the 3-Prong-equipped RC3 produces over 60% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped RC2 or RC3 systems, on this platform, on average.

With a standard untuned MK18, in the free field, an operator is likely to experience a more boomy signature accompanied by less gas blowback with an RC3 vs. an RC2; to most, a “more pleasant” experience in the free field will result with an RC3.  It is likely that the experience may change near reflecting surfaces.  That testing and analysis is the subject of future PEW Science research.

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:

  1. During FRP, and on average, the WARCOMP-equipped RC3 is the loudest silencer to bystanders with its muzzle Suppression Rating of 25.9.

  2. The RC2 is the quietest system at the muzzle, on average, and during FRP, with its muzzle Suppression Rating of 35.4.

  3. The gas leak from the WARCOMP mount lowers the Rating of the RC2 to 29.2 at the muzzle. However, the RC2 with the WARCOMP mount is still quieter in muzzle signature than the RC3 in both FRP and average signature, at the muzzle, regardless of mount used with the RC3.

At the Shooter’s Ear, the following notes apply:

  1. During FRP, the RC2 with the 3-prong is the quietest silencer at the shooter’s ear. However, on average, the RC3 with the 3-Prong is slightly quieter at the ear than the RC2. This trend reversal is not discernable from the average at-ear Suppression Ratings.

  2. The different between FRP severity at the shooter’s ear, between the SCI-SIX and the HUXWRX silencers, is approximately 5%. The performance gap widens on average.

  3. Regardless of FRP or average shot sequences, the RC2 equipped with the WARCOMP mount is significantly louder at the shooter’s ear than the same silencer with the 3-prong flash hider or the RC3 equipped with either mount. The average at-ear Suppression Rating of the RC2 drops from 22.2 to 13.3 when changing from the 3-prong flash hider to the WARCOMP.  The at-ear rating drops from 22.4 to 15.4 with the RC3.

  4. The shooter’s ear hazard reduction with the RC3 is, in fact, superior to that of the RC2, but not during the first shot. And, on average, it is only 1.9% less severe with the 3-Prong. With the WARCOMP, the RC3 is 19.4% less severe to the operator than a WARCOMP-equipped RC2.  This is a direct result of the lack of ejection port blast coalescence with the RC3.

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.  Compare like-colors on the chart with like-colors.

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 relative inner ear damage risk and 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.

6.152.2 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.

6.152.2.1 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 RC2 with the 3-Prong flash hider is postulated to sound the quietest, with the RC3 with the closed-tine WARCOMP flash hider sounding the loudest, during the first shot.

Note that in the lower frequency response regime, the RC3 3-Prong signature is more severe than that from the other silencers. This phenomenon may result in bystanders interpreting the signature from the 3-Prong mounted RC3 silencer as “boomy,” relative to that from the other silencers, and potentially even more “boomy” than a WARCOMP-equipped RC3, as the frequency transition of severity between the two configurations does not occur until 3,000 Hz.  This is likely due to the WARCOMP leak coalescence exacerbating higher frequency response due to the fast rise-time of the pressure release blast load shock compared to the high flow rate of the typical distal jet from the 3-Prong RC3 system.

The boominess of the WARCOMP-equipped RC2 over that of the 3-Prong mounted RC2 is due only to a mount leak, and illustrates how such a blast load leak influences severity in the absence of high distal flow.  The RC3’s boomy nature is similar to that of a high-flow silencer like a HUXWRX FLOW system.  So-called boomy signatures from an RC2 are only possible through blast load leak compromise.

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 RC3 to be less severe during FRP, than those with healthy ears. As noted above, a WARCOMP mounted RC2 has an FRP signature that may induce a more “boomy” impression to bystanders, but not as “boomy” as an RC3 silencer, regardless of mount used with the RC3, due to the higher predicted ear response in the lower frequencies. This phenomenon with the RC3 is not isolated to FRP.

6.152.2.2 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 RC2 with the 3-Prong is again postulated to sound the quietest on average, with the WARCOMP-equipped RC3 again being the loudest, on average.

After FRP, the gap between the WARCOMP-equipped RC2 and the 3-Prong-equipped RC3 is narrower. Again, both silencer configurations 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.  However, the WARCOMP mount leak with an RC2 system, on average, does not approach the type of sustained flow rate (blast load duration) of an RC3 system, regardless of mount.  It is for this reason that the inner ear response below 3,000 Hz is significantly higher with both RC3 configurations, than with either RC2 configuration (see Fig. 5b).

To bystanders, it is likely that a WARCOMP-equipped RC3 will be the loudest configuration, on average, regardless of preexisting hearing damage or mount type used with an RC2.  The higher signature severity occurs throughout the inner ear response frequency range; its “boomy” nature, on average, although mirrored with the 3-Prong-mounted RC2, occurs in addition to its harsher signature above hearing response frequencies of 4,000 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)

6.152.3 Comparisons of Waveforms Measured near the Shooter’s Ear

The sound signatures measured at the operator’s head during the tests of each silencer configuration 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.

6.152.3.1 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 RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped RC2 silencer is the loudest to the shooter, not the WARCOMP-equipped RC3.

Below approximately 2,000 Hz, the WARCOMP-equipped RC2 excites the human inner ear less severely than the WARCOMP-equipped RC3.  This is due to higher distal flow rate from the RC3.  However, ejection port blast coalescence from the RC2 system results in more severe response above 2,000 Hz, and throughout the entire range.  This indicates that during FRP, the WARCOMP-equipped RC3 may sound boomy, but the WARCOMP-equipped RC2 will sound boomy and more harsh to most operators.

Also, during FRP, the 3-prong-mounted RC2 is predicted to be the least severe to the operator. This is due to the silencer’s superior first-round signature suppression performance. The first-round signature of the 3-prong-mounted RC3 is more severe, both in low frequency inner ear response (below ~2,500 Hz) and in overall uncontrolled distal flow rate, resulting in the peak response shown near the 4,500 Hz region and above. 

When the WARCOMP is used with either Surefire silencer, the signature is severe; the inner ear of the shooter during FRP is postulated to respond with greater severity than the 3-Prong-mounted silencer configurations through almost the entire inner ear response range. The WARCOMP gas leak produces severe jetting that excites the ear of the shooter significantly even to 8,500 Hz and above. This inner ear response is the result of shock loading.  It is interesting to note that the 3-Prong-mounted RC3 also induces exaggerated inner ear response above 4,000 Hz, but again, this is due to high uncontrolled distal flow rate.  This is an unusual performance attribute of the RC3.  The RC3 does not provide the first-round signature suppression capabilities of the RC2, to bystanders nor to the shooter.  It is unable to provide this to the shooter, despite its higher flow rate.  Uncontrolled distal flow is the cause of this performance detriment.

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 other Research Supplements, the significantly higher inner-ear response with the WARCOMP-equipped Surefire silencers shows notably higher hearing damage risk to the shooter. The abnormal slope of the response curve above 6,000 Hz and the shock-load measured at the shooter’s ear displayed in the published RC2 Sound Signature Review highlight this severity. PEW Science urges caution when using the WARCOMP mount due to gas leakage and increased hearing damage risk.  It is interesting to note that because the WARCOMP-equipped RC3 signature is also driven by high distal flow rate, and low(er) ejection port blast, the damage slope above 6,000 Hz is steeper (ref. Fig. 6a, linear scale).  This is a direct visual illustration of a quantitative multi-source blast wave coalescence phenomenon: muzzle blast, mount leak, and ejection port blast of the RC2 vs. muzzle blast and mount leak of the RC3.  The lower ejection port blast and different mount leak dynamics result in less high frequency severity with an RC3.  This, again, is also reflected below 2,000 Hz.

During the first shot, almost all shooters will observe all the Surefire silencer configurations to be boomy, other than the 3-Prong-equipped RC2, on this weapon system.

6.152.3.2 Average Ear Comparisons

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, again, 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 3-Prong-equipped RC3 is the quietest silencer. However, the exacerbated low-frequency response of the two RC3 silencers configurations remain, 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 4,500 Hz over the previous generation RC2 technology is noted in the average signatures, unlike during the first shot. This analysis further supports the conclusion that low first-round shot suppression of the RC3 is a significant performance factor.

Even with the “boomy” signature characteristics, the 3-Prong-equipped RC3 produces over 60% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped RC2 or RC3 systems, on this platform, on average.

Fig 7a. Comparison of Average Human Inner Ear Response - 5.56 at the Ear (Linear Scale)

Each of the signature response comparison phenomena examined during FRP in the preceding section is consistent in the average shot string analysis plots, either with reduced intensity due to smoothing from the first shot being only one fifth of dataset, or with persistent phenomenology unaffected by FRP combustion:

  1. The exaggerated response of the WARCOMP-equipped RC3 is still present below 2,000 Hz.

  2. The exaggerated response of the 3-Prong-equipped RC3 has now shifted from below 3,000 Hz to below 2,000 Hz (it is now purely flow-rate dependent instead of uncontrolled combustion driven).

  3. High-frequency WARCOMP response remains due to the persistent mount leak, unaffected by FRP combustion gradient.

On average, the WARCOM-equipped RC2 still induces the highest hearing response to the shooter. The abnormal response curve is maintained over the entire shot sequence. This phenomenon, again, is indicative of the persistent mount gas leak coalescing with ejection port blast and muzzle blast

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 RC3 systems both show plateaus below 2,000 Hz from high distal flow rate, in this average shot analysis, which smooths the influence of the erratic first round suppression phenomenon.  Figure 7b, therefore, shows an extremely succinct summary of what an operator may experience with an RC3 vs. RC2 silencer on the standard untuned MK18, in the free field: a more boomy signature accompanied by less gas blowback; to most, a “more pleasant” experience in the free field.  It is likely that the experience may change near reflecting surfaces.  That testing and analysis is the subject of future PEW Science research.

6.152.4 Research Supplement Summary (Repeated from above)

The RC3 design changes were implemented to address the restrictive flow rate of the RC2.  When implementing the design changes, Surefire addressed the propensity for more severe signature propagation and first-round flash with particular geometric features.  In the final RC3 product, the performance of the system achieves several design goals while compromising some performance attributes of the legacy RC2 system, an introducing some performance challenges.  There may exist other systems with high flow rate that outperform the RC3 with less compromise on the same weapon system.  PEW Science research to compare the performance of these systems, in context, is ongoing.  

The following are detailed signature analysis conclusions for both bystanders and operators using the RC3 and RC2 on a MK18 weapon system, in the free field:

Bystander Perception:

To personnel located 1.0 m left of the weapon muzzle, the RC2 with the 3-Prong flash hider is postulated to sound the quietest, with the RC3 with the closed-tine WARCOMP flash hider sounding the loudest, during the first shot.

Bystanders may interpret the first-round signature from the 3-Prong mounted RC3 silencer as “boomy,” relative to that from the other silencer configurations, and potentially even more “boomy” than a WARCOMP-equipped RC3.  This is likely due to the WARCOMP leak coalescence exacerbating higher frequency response due to the fast rise-time of the pressure release blast load shock compared to the high flow rate of the typical distal jet from the 3-Prong RC3 system.

The boominess of the WARCOMP-equipped RC2 over that of the 3-Prong mounted RC2 is due only to a mount leak, and illustrates how such a blast load leak influences severity in the absence of high distal flow.  The RC3’s boomy nature is similar to that of a high-flow silencer like a HUXWRX FLOW system.  So-called boomy signatures from an RC2 are only possible through blast load leak compromise.

Bystanders with hearing loss above the 3,000 Hz range may perceive the sound delta between the two mounts used with the RC3 to be less severe during FRP, than those with healthy ears. As noted above, a WARCOMP mounted RC2 has an FRP signature that may induce a more “boomy” impression to bystanders, but not as “boomy” as an RC3 silencer, regardless of mount used with the RC3, due to the higher predicted ear response in the lower frequencies. This phenomenon with the RC3 is not isolated to FRP.

On average, the RC2 with the 3-Prong is again postulated to sound the quietest, with the WARCOMP-equipped RC3 again being the loudest.

After FRP, the gap between the WARCOMP-equipped RC2 and the 3-Prong-equipped RC3 is narrower. Again, both silencer configurations 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 RC2 with the 3-prong flash hider is the quietest silencer during the first shot. The WARCOMP-equipped RC2 silencer is the loudest to the shooter, not the WARCOMP-equipped RC3.

Below approximately 2,000 Hz, the WARCOMP-equipped RC2 excites the human inner ear less severely than the WARCOMP-equipped RC3.  This is due to higher distal flow rate from the RC3.  However, ejection port blast coalescence from the RC2 system results in more severe response above 2,000 Hz, and throughout the entire range.  This indicates that during FRP, the WARCOMP-equipped RC3 may sound boomy, but the WARCOMP-equipped RC2 will sound boomy and more harsh to most operators.

During FRP, the 3-prong-mounted RC2 is predicted to be the least severe to the operator. This is due to the silencer’s superior first-round signature suppression performance. The first-round signature of the 3-prong-mounted RC3 is more severe, both in low frequency inner ear response (below ~2,500 Hz) and in overall uncontrolled distal flow rate, resulting in the peak response shown near the 4,500 Hz region and above. 

The 3-Prong-mounted RC3 also induces exaggerated inner ear response above 4,000 Hz, but this is due to high uncontrolled distal flow rate.  This is an unusual performance attribute of the RC3.  The RC3 does not provide the first-round signature suppression capabilities of the RC2, to bystanders nor to the shooter.  It is unable to provide this to the shooter, despite its higher flow rate.  Uncontrolled distal flow is the cause of this performance detriment.

The lower ejection port blast and different mount leak dynamics result in less high frequency severity with an RC3.  During the first shot, almost all shooters will observe all the Surefire silencer configurations to be boomy, other than the 3-Prong-equipped RC2, on this weapon system.

To personnel firing the weapon, on average, the 3-Prong-equipped RC3 is the quietest silencer. However, the exacerbated low-frequency response of the two RC3 silencers configurations remain, due to flow rate, which may again result in the “boomy” perception to the shooter. This analysis further supports the conclusion that low first-round shot suppression of the RC3 is a significant performance factor.

Even with the “boomy” signature characteristics, the 3-Prong-equipped RC3 produces over 60% less severe hearing damage potential to the shooter, compared to the WARCOMP-equipped RC2 or RC3 systems, on this platform, on average.

With a standard untuned MK18, in the free field, an operator is likely to experience a more boomy signature accompanied by less gas blowback with an RC3 vs. an RC2; to most, a “more pleasant” experience in the free field will result with an RC3.  It is likely that the experience may change near reflecting surfaces.  That testing and analysis is the subject of future PEW Science research.