SSS.6.101 - CGS SCI-SIX and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)
/CGS SCI-SIX on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The SCI-SIX is designed by CGS Group. It is a centerfire rifle silencer intended for use on semiautomatic and automatic 5.56x45mm host weapons, with no barrel length restrictions. The silencer mounts to the host firearm with a flash hider mount that LH threads to the silencer body. It has a 1.64-inch primary diameter and is 6.5 inches long with the mount installed. The main silencer body is constructed from 718 Inconel using additive manufacturing (DMLS 3D printing). The end cap of the silencer is removable and changeable; the tested end cap has the same aperture as the CGS Helios and Hyperion family of end caps. The silencer weighs 17 ounces and with the included flash hider mount, the total system weight is 19.6 ounces, as tested. The SCI-SIX can be obtained from Silencer Shop.
PEW Science is an independent private testing laboratory and also the world’s only publicly funded suppressed small arms research cooperative. Testing, data analysis, and reporting is generated with funding provided by PEW Science members. Any test data that is generated with any portion of private funding contains this disclosure. The testing and data production for this Sound Signature Review was funded in part by PEW Science Project PEW-CGS-052-22. Therefore, data pertaining to the SCI-SIX in this Sound Signature Review is published with the express written permission of CGS Group, LLC.
The SCI-SIX Program is a research and development (R&D) effort requested by the end-user entity SC IRREGULARS. High level summaries of the SCI-SIX Program Overview, Validation Effort, and Program Results are presented in Section 6.101.1 of this Review.
This Sound Signature Review contains single-test results using the selected variant of the CGS SCI-SIX with the flash hider mount on the MK18 Automatic AR15 rifle, chambered in 5.56x45mm NATO with a 10.3-inch barrel. Federal XM193 55gr ammunition was used in the test. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51. The Member version of this Review also contains R&D variant test results analysis. PEW Science thanks you for your support.
Section 6.101.1 contains a high level description of the SCI-SIX Program Overview, Validation Effort, and Program Results.
Section 6.101.2 contains the SCI-SIX test results and analysis for the selected variant.
Section 6.101.3 contains data on the CGS SCI-SIX Program variant selection and third-party validation (Members Only).
Section 6.101.4 contains Suppression Rating comparisons of the selected SCI-SIX with dedicated 223 and 30 caliber silencers on the current market, including the Dead Air Nomad-30, YHM Turbo T2, Dead Air Sandman-S, HUXWRX FLOW 556k, Energetic Armament ARX, KAC QDSS-NT4, Rugged Razor556, Otter Creek Labs Polonium and Polonium-K, Surefire SOCOM556-RC2, HUXWRX HX-QD 556 and HX-QD 556k, Q Trash Panda, CGS Helios QD, SilencerCo Saker 556, Rugged Razor762, and others.
Section 6.101.5 contains the review summary and PEW Science subjective opinions.
Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the CGS SCI-SIX mounted with the flash hider mount achieved a composite Suppression Rating™ of 34.7 in PEW Science testing. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
Relative Suppression Rating Performance is Summarized in SSS.7 - PEW Science Rankings
6.101.1 The CGS // SC IRREGULARS SCI-SIX Program
The following is a high level description of the administrative structure and technical validation effort of the SCI-SIX program.
6.101.1.1 Program Overview
The SCI-SIX Program is an R&D effort requested by the end-user entity SC IRREGULARS. CGS Group was solicited for the program and is the program manager. The SCI-SIX Program roles are defined below:
Solicitation Author: SC Irregulars LLC
Program Manager: CGS Group, LLC
Designer: CGS Group, LLC
End-User Field Performance Validation (Group 1): SC Irregulars LLC
End-User Field Performance Validation (Group 2): Noveske Rifleworks LLC Pizzaboiis
Test Laboratory Performance Validation (Group 3): PEW Science, LLC
Multiple SCI-SIX silencer R&D variants were designed and manufactured. The three Performance Validation Groups were tasked to independently evaluate the performance of the silencer variants, and to report their findings to the program manager. Communications between the groups and from each group to the program manager regarding the evaluations were firewalled.
6.101.1.2 Validation effort
Field Performance Validation of the SCI-SIX variants by Group 1 and Group 2 was performed using multiple 5.56x45mm weapon systems. Weapon systems included semiautomatic and automatic direct gas impingement AR15 rifles with barrel lengths primarily between 10-inches and 12-inches. The primary host weapon system used by Group 1 was an 11.5-inch barrel rifle possessing a mid-length gas system.
Test Laboratory Performance Validation of the SCI-SIX variants by Group 3 was performed only using the standard PEW Science MK18 test host weapon system described in Public Research Supplement 6.51.
6.101.1.3 Program results
The SCI-SIX Program resulted in the successful downselection of an SCI-SIX silencer variant. All three Performance Validation Groups selected a variant that exhibited the most favorable overall performance characteristics. The variant selection across groups was unanimous. The following technical notes apply to the downselection:
Performance characteristics of note, across variants, were common across Groups. For example, severe signature or restrictive flow rate, if possessed by a variant, was noted by both Field Validator experience and the Laboratory Validator test data and analysis.
Delineation of the performance gradients across variants was also common across Groups. Anecdotal and subjective user experiences from Field Validators were consistent with quantitative Laboratory Validation data. For example, variants with very similar performance characteristics exhibited similar Field Rankings and Laboratory Rankings. Engineering analysis using the Suppression Rating was performed, as using only peak pressure [dB] and impulse [dB-ms] measurements, alone, did not offer meaningful or useful performance insight across variants.
The selected SCI-SIX variant represents both a practical and technical performance design compromise for the Solicitation Author (end-user entity). At the conclusion of the program, the variant performance decision was unanimous across groups and agreed upon by the Program Manager. The variant exhibiting the highest overall performance was selected to be the production silencer by the Program Manager and the Solicitation Author.
6.101.2 CGS SCI-SIX Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the CGS SCI-SIX tested with the flash hider mount is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. The data acquired 0.15 m (6 in) right of the shooter’s ear is only available to membership supporters of PEW Science and the Silencer Sound Standard. 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.
Table 1. CGS SCI-SIX Sound Metric Summary
6.101.2.1 SOUND SIGNATURES AT THE MUZZLE
Real sound pressure histories from a 6-shot test acquired with PEW-SOFT™ are shown below. Six cartridges were loaded into the magazine, the fire control group positioned to single-shot, and the weapon was fired until the magazine was empty and the bolt locked back on the follower of the empty magazine. Only five shots are considered in the analysis. The signatures of Shot 6 are displayed in the data presentation but are not included in the analysis to maintain consistency with the overall PEW Science dataset and bolt-closing signatures. The waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science testing is 1.0 MS/s (1 MHz). The peaks, shape, and time phasing (when the peaks occur in relation to absolute time and to each other) of these raw waveforms are the most accurate of any firearm silencer testing publicly available. PEW-SOFT data is acquired by PEW Science independent testing; the industry leader in silencer sound research. For more information, please consult the Silencer Sound Standard.
The primary sound signature pressure histories for all 6 shots with the SCI-SIX are shown in Figure 1a. The sound signatures of Shot 1 and Shot 2 are shown in Figure 1b, in early time. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 2a. In Figure 2b, a shorter timescale is shown comparing the impulse of Shots 1 through 3.
Fig 1a. CGS SCI-SIX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. CGS SCI-SIX 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. CGS SCI-SIX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. CGS SCI-SIX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The CGS SCI-SIX is an evolution of the Helios family of rifle silencers and shares many design similarities. The SCI-SIX uses legacy CGS rifle silencer technology, and is intended to be adaptable with end cap changes. However, unlike the Helios family, the SCI-SIX is intended to be used exclusively with the 5.56x45mm cartridge. The primary technical differences between the Helios family and the SCI-SIX are:
The SCI-SIX is smaller in diameter.
The SCI-SIX is DMLS Inconel, whereas only the Helios QD in the Helios family is available in Inconel; the rest of the Helios variants are constructed of Grade 5 titanium.
Direct blast chamber venting and a different blast chamber / baffle configuration.
Dedicated mount threading to the silencer body, fixing the distance of the muzzle jet to the first orifice.
Other technical differences also exist in the silencer, but are beyond the scope of this article. Principally, the SCI-SIX operates as a restricted bore Helios with advanced venting; it possesses ancillary venting that occurs earlier in the geometry than a Helios DT / Hyperion K. This allows the SCI-SIX to exhibit a higher flow rate in early time than typical for its bore. The venting directs to a portion of the annulus; a common geometric feature of CGS rifle silencers, including the Hyperion family.
One consequence of the flow rate exhibited by the selected SCI-SIX variant is somewhat noticeable first round pop (FRP). However, the FRP is not severe; a key factor in the selection of the variant. The significant FRP divergence in pressure space (Figure 1b) is noted in both the positive and negative phase (rarefaction). However, the expedient rarefaction also results in significant impulse decay (Figure 2a). This impulse decay is favorable to the FRP signature; similar decay with favorable characteristics was noted in the Dead Air Nomad-30 MK18 test (Review 6.100).
PEW Science Research Note 1: The consistency of the SCI-SIX after FRP is notable; Shot 2 normalizes relatively quickly after the primary jet. The stabilized blowdown of the silencer (Figure 2a and enhanced view in Figure 2b) is extremely consistent across shots. The selected variant resulted in the most consistent signature of the variants tested in the SCI-SIX R&D program. Consistency of silencers on the MK18 in the impulse regime is relatively unusual; the Otter Creek Labs Polonium (Review 6.75) is another silencer that exhibits relatively high consistency after FRP. However, it is interesting to note that despite the Polonium exhibiting a higher overall muzzle (bystander) Suppression Rating than the SCI-SIX, the Polonium exhibits a more severe relative FRP signature to subsequent shots. That is, the difference in severity between the Polonium’s first shot and follow-up shots is more severe than that of the SCI-SIX, to bystanders, on the MK18.
PEW Science Research Note 2: As illustrated in the testing and analysis of the CGS Helios QD MK18 data (Review 6.66) and the Nomad-30 on the MK18, secondary combustion from the 10.3 inch barrel may be controlled through the use of advanced baffle elements possessing ancillary venting to annular space. As the bore is restricted and additional venting is added early in the flow field, this performance trait is further enhanced. The consistency described in Research Note 1 is a direct, objective illustration of 5.56x45mm performance optimization. Other types of optimizations have been analyzed and presented by PEW Science in previous Sound Signature Reviews, such as:
The optimization of the Rugged Razor556 (Review 6.76) for MK18 performance compared to that of the Rugged Razor762 (Review 6.58). Optimizations included removal of a baffle and varying baffle spacing in order to facilitate more efficient 5.56x45 jet expansion. End cap orifice nozzle changes were also employed. The Razor556 is, essentially, a non-modular Micro30.
The optimization of the YHM Turbo T2 (Review 6.98) in which the perforated blast baffle allows expedient jet expansion into relatively large interstitial baffle expansion regions for the total volume.
The, perhaps unintended, optimization of the Q Trash Panda (Review 6.61) in which generous expansion chamber volumes coupled with porting result in efficient 5.56x45mm jet expansion. This optimization is notable due to the design’s lack of optimization for the 7.62x51mm NATO combustion regime; a trait that results in a reversal of its performance efficiency compared to some other 30 caliber rifle silencers like the aforementioned Nomad-30 and Helios QD.
The flow rate of the CGS SCI-SIX is higher than that of many dedicated silencers for the cartridge, including the YHM Turbo T2 (Review 6.98), Otter Creek Labs Polonium (Review 6.75), Polonium-K (Review 6.95), Surefire SOCOM556-RC2 (Review 6.52), SilencerCo Saker 556 (Review 6.53), and KAC QDSS-NT4 (Review 6.78). The SCI-SIX does not possess a flow rate as high as the OSS HX-QD 556 (Review 6.54), OSS HX-QD 556k (Review 6.64), or the HUXWRX FLOW 556K (Review 6.83). Testing and analysis of different end cap geometries with the SCI-SIX is the subject of further SCI-SIX Program research.
PEW Science Research Note 3: As in all semiautomatic AR15 weapon testing, a second pressure pulse originates from the ejection-port signature of the weapon and it occurs early enough in time such that its waves coalesce with that of the muzzle signature. However, in late time (at approximately 80 ms in Figure 1a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 does not display this event due to the bolt remaining open after the sixth and final round is fired from the magazine.
PEW Science Research Note 4: The closing time of the MK18 bolt is directly related to the flow restriction of a silencer for a given weapon system. PEW Science has determined bolt closing time variation from the unsuppressed state to be a reliable indicator of silencer back pressure, with strong correlation with the PEW Science Back Pressure Metric, Omega. However, PEW Science has also determined that the indicator is unreliable upon upper receiver fouling. Sound signatures are not influenced by this fouling, as these kinematics occur in late time, after gas venting to atmosphere. Momentum transfer, weapon condition (upper receiver fouling), and other factors, can significantly influence bolt closing time. PEW Science urges the reader to exercise extreme caution if using the published bolt closing time to make determinations regarding silencer flow restriction (back pressure) or weapon system kinematics. This type of calculation may provide erroneous results, as the weapon condition at the time of each test is not published data. The time-scale duration showing bolt closing time is only published by PEW Science such that the signature data pedigree may be verified.
The shape, timing, and magnitudes of the early-time pressure pulses and overall shape of the impulse waveforms measured at the muzzle, from shot-to-shot, are relatively consistent, until the aforementioned late-time irregularities resulting from primary axial over-bore.
As typically indicated, first-round sound signatures always differ from subsequent shots, as the atmosphere within the silencer changes. The FRP phenomenon cannot always be shown by viewing only the peak sound pressure. This is one of the reasons why The Silencer Sound Standard requires examining multiple sound signature metrics. Ammunition consistency can play a role in the determination of FRP, however, the close examination of measured pressure and impulse waveforms typically excludes ammunition from the possible factors influencing true FRP, due to the relative consistency of most high quality factory ammunition.
PEW Science Research Note 5: Note that the muzzle Suppression Rating of the CGS SCI-SIX with the flash hider mount is 34.0 and the shooter’s-ear Suppression Rating is 24.5; different zones on the Suppression Rating Dose Chart. Of high performance dedicated-bore, non-flow-through 5.56x45mm silencers evaluated by PEW Science on the MK18, the CGS SCI-SIX exhibits some of the most balanced performance characteristics on the standard MK18 weapon system. Holistic suppression performance comparisons on the MK18 weapon system are examined in the section below.
6.101.4 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 6 presents a comparison of the PEW Science Suppression Rating of the selected CGS SCI-SIX variant with the flash hider mount to that of other rifle silences on the MK18 automatic AR15 rifle. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Figure 6. Suppression Rating Comparisons of the CGS SCI-SIX and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
From the above data, it can be concluded that the selected silencer variant of the SCI-SIX Program significantly outperforms many silencers on the standard MK18 weapon system, holistically. The muzzle (bystander) Suppression Rating approaches that of the Surefire SOCOM556-RC2 (Review 6.52), and it does so with a higher flow rate and significantly larger end cap orifice, while being the same length. The shooter’s ear (operator) Suppression Rating eclipses that of any non-flow through silencer shown in Figure 6. Notably, its suppression performance for the MK18 weapon operator is higher than that of the HUXWRX (OSS) HX-QD 556K (Review 6.64), as well as higher than that of the KGM R556 (Review 6.60). This is notable, given the ancillary distal venting possessed by those two silencers.
The CGS SCI-SIX possesses a Suppression Rating at the shooter’s ear that is almost half a category higher than that of the Otter Creek Labs Polonium (Review 6.75) on the standard MK18. While the Polonium does possess a less severe muzzle signature, the performance differential to the operator is more pronounced.
Readers may note the stark contrast in performance between the SCI-SIX and the Helios QD (direct thread) on the MK18, in the tested configurations. Two technical differences between the silencers are repeated here from Section 6.101.2.1, above:
The SCI-SIX possesses direct blast chamber venting and a different blast chamber / baffle configuration.
The SCI-SIX possesses dedicated mount threading to the silencer body, fixing the distance of the muzzle jet to the first orifice.
The above two technical differences between the silencers result in significant performance differential on the MK18. Note that the CGS Helios DT, Hyperion K, and Hyperion exhibit completely different early-time gas dynamics. Testing and analysis of these geometries is the subject of future PEW Science publication.
Another notable comparison is that of the CGS SCI-SIX and the Otter Creek Labs Polonium-K (Review 6.95). The SCI-SIX is quieter to bystanders than the Polonium-K, and the difference in signature severity to the operator is more pronounced. Although the SCI-SIX is approximately an inch longer, this performance differential still highlights the significant differences in the silencers’ designs and when viewed in context with that of the full-size Polonium performance on the MK18, provides the state of practice an objective look at balanced performance-based design potential.
Since the inception of the Surefire SOCOM556-RC2, balanced silencer performance on the MK18 has objectively been proven feasible. PEW Science considers the results of the CGS SCI-SIX Program to be another objective display of balanced performance on the weapon system in the same length envelope, with similar operational features. For the selected SCI-SIX variant to achieve even more balanced performance on the MK18 than the SOCOM556-RC2, with greater durability and lighter weight, is extremely notable. The independent 3-tier third party performance validation case study presented herein highlights the design efficacy.
6.101.5 Review Summary: CGS SCI-SIX on the MK18 5.56x45mm AR15 with 10.3-in Barrel
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the CGS SCI-SIX mounted with the flash hider mount achieved a composite Suppression Rating™ of 34.7 in PEW Science testing. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
PEW Science Subjective Opinion:
The CGS SCI-SIX is a is a full-size 5.56mm machine gun rated rifle silencer constructed of DMLS (3D-printed) Inconel 718. It exhibits high performance on the MK18 weapon system and is demonstrated to be one of the most balanced high performance designs on the current market, with extreme durability and lighter weight than some legacy designs. The production variant is the result of a multi-tiered third party performance evaluation process in a solicitation that was created by the end-user entity SC IRREGULARS. It is the first CGS production rifle silencer to feature a dedicated muzzle device mount.
The CGS SCI-SIX is an evolution of the Helios family of rifle silencers and shares many design similarities. The SCI-SIX uses legacy CGS rifle silencer technology, and is intended to be adaptable with end cap changes. However, unlike the Helios family, the SCI-SIX is intended to be used exclusively with the 5.56x45mm cartridge. The primary technical differences between the Helios family and the SCI-SIX are a smaller diameter, exclusively Inconel construction (no titanium model), direct blast chamber venting and different blast chamber / baffle configuration, and dedicated mount threading to the silencer body, fixing the distance of the muzzle jet to the first orifice. Other technical differences also exist in the silencer, but are beyond the scope of this article. Principally, the SCI-SIX operates as a restricted bore Helios with advanced venting; it possesses ancillary venting that occurs earlier in the geometry than a Helios DT / Hyperion K. This allows the SCI-SIX to exhibit a higher flow rate in early time than typical for its bore. The venting directs to a portion of the annulus; a common geometric feature of CGS rifle silencers, including the Hyperion family.
Since the inception of the Surefire SOCOM556-RC2, balanced silencer performance on the MK18 has objectively been proven feasible. PEW Science considers the results of the CGS SCI-SIX Program to be another objective display of balanced performance on the weapon system in the same length envelope, with similar operational features. For the selected SCI-SIX variant to achieve even more balanced performance on the MK18 than the SOCOM556-RC2, with greater durability and lighter weight, is extremely notable. The independent 3-tier third party performance validation case study presented herein highlights the design efficacy.
The silencer has changeable end-caps; evaluation of this feature is the subject of future PEW Science research. Readers should note that the tested end cap possesses an identical aperture to the Helios and Hyperion family of silencers.
Tolerance stacking with variable end-caps is sometimes an issue. However, as the SCI-SIX is 3D printed, it is possible that manufacturing tolerances of the “core” section may be controlled more easily than in traditional manufacturing; PEW Science does not anticipate any issues. The repeatability, concentricity, and general alignment of 3D printed designs and their interface with machined parts is a subject of continued research interest. As 3D-printed parts continue to be introduced into silencer component manufacturing, designs are expected to evolve.
The left-hand (LH) threaded taper mount from CGS is simple to operate. It may be installed on the weapon system with an adjustable wrench; the mount body, itself, serves as wrench-flats. The mount also possesses rear wrench flat features that may be used should the mount need to be removed from the silencer without a host weapon present. However, as the silencer is LH threaded to the mount one can tighten the entire assembly to a conventionally right-hand (RH) threaded barrel muzzle, and continued RH tightening will subsequently loosen the silencer from the mount. Although proper mount installation torque mitigates such a solution from being absolutely necessary, this mechanical feature is welcome for practicality.
The internal baffle geometry of the SCI-SIX, like the Helios QD, is patented and referred to as Hyperion Technology, present in all CGS rifle silencers. The blast chamber vents flow into two primary directions; a main axial flow path and a coaxial outer flow path. The SCI-SIX vents earlier and differently than the Helios QD. The utilization of the coaxial chamber is unique, in that main axial flow is introduced into existing coaxial flow approximately halfway forward of the blast baffle. In addition to this secondary flow introduction, the coaxial chamber may be vented to atmosphere at the forward section of the silencer by the use of a variety of end caps.
The SCI-SIX is extremely durable and has undergone a significant amount of automatic and semi-automatic sustained fire testing by SC IRREGULARS and Noveske Rifleworks, with no apparent damage. Interested parties are encouraged to contact CGS for more information on such third-party field validation. The SCI-SIX has no barrel length restrictions or firing schedule restrictions.
In this review, the SCI-SIX performance metrics depend upon suppressing a supersonic centerfire rifle cartridge on a short barrel gas-operated rifle, which is an incredibly difficult task. PEW Science encourages the reader to remain vigilant with regard to all supersonic centerfire rifle suppression claims. The gas volume and combustion products created by the firing of the supersonic 5.56x45mm cartridge are significant; the measured pressure and impulse magnitudes, and their durations, illustrate this fact. Silencer performance on automatic (reciprocating) rifles depends on many factors. Weapon configuration may significantly influence total suppressed small arm system performance.
The hearing damage potential of supersonic centerfire rifle use is significant. PEW Science encourages the reader to consider the Suppression Rating when deciding on an appropriate silencer and host weapon combination for their desired use.
