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

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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.

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 due to design changes are apparent and noted.  This supplement is part of ongoing PEW Science small arm weapon system sound signature research.

In the Member Version of article 6.151 examining the SOCOM556-RC3, there is also 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. The full version of this article is only available to members. You can support PEW Science testing, research, and development with a membership, here. State-of-the-art firearm sound signature testing and research conducted by PEW Science is supported by readers like you. Thank you for your support!