SSS.6.128 - Surefire SOCOM556-RC2 and the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle
/Surefire SOCOM556-RC2 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
The SOCOM556-RC2 is manufactured by Surefire. It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm NATO cartridge from barrels greater than or equal to 10 inches in length. It has a 1.5-inch diameter and is 6.4 inches long. The silencer mounts to the host firearm with a proprietary mounting system; the user may choose from various Surefire flash hider and muzzle brake mounts. The outer tube and end cap are constructed of heat treated stainless steel. The baffles are constructed of Inconel steel alloy. As tested, the silencer weighs 16.9 ounces and the 3-prong flash hider weighs 3.9 ounces, for a total system weight of 20.8 ounces. The SOCOM556-RC2 can be obtained from Silencer Shop.
This review contains results from two separate tests. PEW Science tested the SOCOM556-RC2 on the M4A1 with the SOCOM 3-Prong flash hider mount and also with the WARCOMP closed-tine flash hider mount. The SOCOM 3-Prong flash hider mount is non-ported and contains so-called “labyrinth seals.” The presence of the seal rings, and more importantly the lack of ports, results in the 3-prong flash hider system exhibiting significantly different gas dynamics than does a ported WARCOMP-equipped SOCOM556-RC2 system. Similar phenomena were measured and analyzed in previous testing as summarized in the following white papers:
Cautions:
The WARCOMP mount increases postulated hazards in all tested regimes. Personal protective equipment (PPE), including eye and ear protection, is recommended for the operation of suppressed small arms, in general.
This is not a 10.3-in barrel MK18 dataset. Any performance similarities with this silencer on the M4A1 and the MK18 platforms is coincidental and a function of the holistic suppressed weapon system characteristics (the silencer in combination with the weapon). Extrapolation of testing and analytical results to and from each weapon system may produce erroneous and potentially unconservative conclusions. Personnel hazards do not scale directly nor linearly between the two host weapon systems.
Both sets of test results in this Sound Signature Review are of the SOCOM556-RC2 on the M4A1 Mid-Gas Automatic AR15 rifle, chambered in 5.56x45mm NATO with a 14.5-inch barrel. Federal XM193 55gr ammunition was used in the tests. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127.
Section 6.128.1 contains test results and analysis using the SOCOM 3-Prong flash hider mount.
Section 6.128.2 contains test results and analysis using the WARCOMP closed-tine flash hider mount.
Section 6.128.3 contains a comparison of the sound signatures of the two mount systems, along with a detailed comparison of the performance of the SOCOM556-RC2 silencer on the M4A1 and MK18 host weapon systems (Members Only).
Section 6.128.4 contains overall gross Suppression Rating comparisons of all tested systems.
Section 6.128.5 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the Surefire SOCOM556-RC2 mounted with the SOCOM 3-Prong flash hider achieved a composite Suppression Rating™ of 35.7 in PEW Science testing. When mounted with the WARCOMP flash hider on the same host weapon and fired with the same ammunition, the SOCOM556-RC2 achieved a composite Suppression Rating of 32.8.
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Surefire SOCOM556-RC2 mounted with the SOCOM 3-Prong flash hider also achieved a composite Suppression Rating™ of 35.7 in PEW Science testing. When mounted with the WARCOMP flash hider on the same host weapon and fired with the same ammunition, the SOCOM556-RC2 achieved a composite Suppression Rating of 29.4.
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
6.128.1 SOCOM556-RC2 Sound Signature Test Results (SOCOM 3-Prong Flash Hider)
A summary of the principal Silencer Sound Standard performance metrics of the Surefire SOCOM556-RC2 with the 3-Prong Flash Hider is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. This is a members-only review and includes pressure and impulse waveforms measured at the shooter’s ear. PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
Table 1. Surefire SOCOM556-RC2 (3-Prong FH) Sound Metric Summary
6.128.1.1 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 public dataset and bolt-closing signatures. The waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science laboratory sound signature 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 laboratory testing; the recognized 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 SOCOM556-RC2 with the 3-Prong Flash Hider 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 Shot 1 to that of Shot 2 and Shot 3.
Fig 1a. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature
Figure 2a. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
“The Surefire SOCOM556-RC2 was the first silencer evaluated by PEW Science on the standard MK18 weapon system and subsequently included in the public Silencer Sound Standard research pedigree in Sound Signature Review 6.52. Since that publication, the pedigree has grown to include a significant amount of data and analysis, and as a result, the understanding of the suppressed MK18 weapon system by this laboratory, the industry, and the public, has significantly increased. The SOCOM556-RC2 was designed by Surefire to complement the MK18; to perform efficiently in the combustion environment produced by the extremely short 10.3-in 5.56x45mm gun barrel. We encourage the reader to keep this in mind when reviewing the data and analysis in this white paper. The performance of the silencer on the standard M4A1 weapon system is extremely similar to that of its performance on the MK18. In our subjective opinion, this is both a positive and a negative. For a specialized silencer to maintain performance across systems, years after its initial intended development has ceased, is notable. However, a design so dependent upon pressure input for efficacy may limit the utility of the silencer for those end-users pursuing absolute performance on multiple platforms. Furthermore, if the specialized nature of a silencer is not showcased, analyzed, understood, and disseminated to the public, the state of practice stalls. In keeping with the PEW Science mission, the prolific SOCOM556-RC2 is again showcased here in a manner never before seen, this time on the 14.5-in barrel M4A1 mid-length gas platform. As fielding of that weapon system increases, we are pleased at the prospect of the conclusions from this internally-funded research program proliferating and assisting end-users for years to come, as has been the case with our WARCOMP research.”
PEW Science Laboratory Personnel Note: The Surefire SOCOM556-RC2 was the first silencer evaluated by PEW Science on the standard MK18 weapon system and subsequently included in the public Silencer Sound Standard research pedigree in Sound Signature Review 6.52. Since that publication, the pedigree has grown to include a significant amount of data and analysis, and as a result, the understanding of the suppressed MK18 weapon system by this laboratory, the industry, and the public, has significantly increased. The SOCOM556-RC2 was designed by Surefire to complement the MK18; to perform efficiently in the combustion environment produced by the extremely short 10.3-in 5.56x45mm gun barrel. We encourage the reader to keep this in mind when reviewing the data and analysis in this white paper. The performance of the silencer on the standard M4A1 weapon system is extremely similar to that of its performance on the MK18. In our subjective opinion, this is both a positive and a negative. For a specialized silencer to maintain performance across systems, years after its initial intended development has ceased, is notable. However, a design so dependent upon pressure input for efficacy may limit the utility of the silencer for those end-users pursuing absolute performance on multiple platforms. Furthermore, if the specialized nature of a silencer is not showcased, analyzed, understood, and disseminated to the public, the state of practice stalls. In keeping with the PEW Science mission, the prolific SOCOM556-RC2 is again showcased here in a manner never before seen, this time on the 14.5-in barrel M4A1 mid-length gas platform. As fielding of that weapon system increases, we are pleased at the prospect of the conclusions from this internally-funded research program proliferating and assisting end-users for years to come, as has been the case with our WARCOMP research.
As referenced in the above note, the performance of the SOCOM556-RC2 on the M4A1 weapon system is extremely similar to that on the standard MK18. This conclusion is significant. In PEW Science internal laboratory testing, a silencer’s gross signature suppression performance typically increases proportionally to a drop in peak blast pressure input. This performance scaling is a result of proximal silencer geometry. In the case of the SOCOM556-RC2, there is a key design differentiator that prohibits the silencer from providing increased performance on a 14.5-in barrel.
PEW Science Research Note 1: The Surefire SOCOM556-RC2 possesses proximal venting adjacent to the first expansion chamber (blast chamber) that is “active” upon high pressure flow above a certain threshold. Impulse accumulation within the blast chamber is a function of the muzzle uncorking pressure, duration, and subsequent additive shock reflections. PEW Science postulates that below the threshold pressure input, pressure differentials that form ahead of the vent geometry prevent a proportion of combustion gasses from being forced into the annular cavity. As blow-down continues, more gas is forced through the primary orifice. While still active, the annulus is not utilized as effectively. The end result is external pressure output that is extremely similar on a 14.5-in barrel to a 10.3-in barrel. The overall suppression performance of the RC2 with the 3-Prong Flash Hider Mount does not appreciably increase when lengthening the barrel by 40%. It stands to reason that the performance should increase on barrels of 18-in or 20-in in length, however. Those evaluations are outside the scope of this article. Further research is needed.
PEW Science Research Note 2: The first-round-pop (FRP) signature of the silencer on the 14.5-in barrel M4A1, to bystanders, is nominally less severe than on the 10.3-in barrel MK18. This may indicate that the blast chamber pressure differential between FRP and subsequent shots is high enough to accumulate additional impulse that “activates” the annular gas path in the silencer during the first shot. More exhaustive testing is needed to verify this postulation.
PEW Science Research Note 3: The above phenomenon is not without precedent. Although somewhat rare, nonlinear pressure-input-dependent behavior has been observed by PEW Science in other silencer technologies. Surefire Total Signature Reduction Technology shares some similarities in proximal geometry with that of CGS Hyperion Technology. And, like in the case of the Surefire Technology, the CGS Technology has demonstrated pressure input-dependent behavior. This behavior is illustrated in the performance of the Helios QD across combustion regimes, as well as the Hyperion and Hyperion K family of silencers. By changing pressure input amplitude location, different portion(s) of the silencers may be utilized; a phenomenon that varies in the time domain. As silencer technology continues to advance, and high flow rate designs proliferate further, PEW Science postulates the propensity for this behavior to potentially increase.
Just like on the MK18, the Surefire SOCOM556-RC2 is not as restrictive as some other silencers, and therefore somewhat reduces the propensity for severe ejection port blast load at the operator’s head. As further research using the M4A1 14.5-in barrel host weapon system is published by PEW Science, comparisons with other silencer models will be made.
PEW Science Research Note 4: 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 5: The closing time of the AR15 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 and the alpha parameter. 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. The consistency of the waveform amplitudes highlight the silencer’s overall sound performance consistency at the muzzle after the FRP, as well as the relative consistency of the tested automatic rifle firearm configuration.
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 6: Note that the muzzle Suppression Rating of the SOCOM556-RC2 with the 3-Prong mount is 35.0 and the at-ear Suppression Rating is 25.4; different zones on the Suppression Rating Dose Chart. The back pressure of the SOCOM556-RC2 contributes to a more severe ejection port blast signature, increasing the overall severity of the signature to the shooter on the standard M4A1 weapon system. The WARCOMP mount may further increase this shooter hazard, as examined in Section 6.128.2.
The signatures measured at the shooter’s ear are presented below.
6.128.1.2 SOUND SIGNATURES AT SHOOTER’S EAR
Real sound pressure histories from the same 6-shot test acquired with PEW-SOFT at the shooter’s ear are shown below. Again, 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 primary sound signature pressure histories at the ear for all 6 shots are shown in Figure 3. The primary sound signature history is shown in Figure 3a. An annotated timescale is displayed in Figure 3b, for Shots 1 and, 2. The real sound impulse (momentum transfer potential) histories at the ear from the same 6-shot test are shown in Figure 4. Again, full and short timescales are shown.
Figure 3a. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature
Figure 3b. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Figure 4a. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature
Figure 4b. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature Peaks
There are specific differences between the 10.3-in barrel MK18 weapon platform and the 14.5-in barrel M4A1 weapon platform that may significantly influence the hazard to the weapon operator:
Barrel length.
Gas system length.
Gas port size.
The dwell time of the AR15 weapon system (the time required for the bullet to pass the gas port and reach the muzzle to uncork) is a function of factors (1) and (2). The combination of dwell time with factor (3) dictates weapon gas system impulse. Gas system impulse, in combination with barrel shock, dictates overall reciprocation behavior.
There are immediate differences apparent between the MK18 RC2 signatures and the M4A1 RC2 signatures, above. The most notable difference is the back-loaded FRP impulse shown in Figure 4b. This phenomenon is discussed in the MK18 vs. SURG tuning comparison in article 6.111 (Maxim DSX SURG). On the MK18 weapon system, the muzzle signature contribution to the gas momentum accumulation at the operator’s head occurred in a greater proportion than that of the ejection port blast. Two factors change this blast load balance at the operator’s head on the M4A1 with this silencer:
Muzzle blast standoff from the operator’s head has increased.
Ejection port blast is more severe due to longer dwell time, as discussed above.
PEW Science Research Note 7: Serendipitously, the SOCOM556-RC2 possesses a high enough gross flow rate (low enough Omega) and an efficient enough early-time blast chamber vent regime (minimizing alpha) such that the decrease in operator hazard from muzzle blast standoff outweighs the potential ejection port blast increase on this weapon system and the net result is a shooter’s ear Suppression Rating that is slightly less severe than on the MK18. As further M4A1 research is presented by PEW Science, the performance of other silencers on this weapon system will be compared.
6.128.2 SOCOM556-RC2 Sound Signature Test Results (WARCOMP Flash Hider)
A summary of the principal Silencer Sound Standard performance metrics of the SOCOM556-RC2 with the WARCOMP Closed-Tine Flash Hider is shown in Table 2. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. As stated in Section 6.128.1, this is a members-only review and includes pressure and impulse waveforms measured at the shooter’s ear. PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
Table 2. Surefire SOCOM556-RC2 (WARCOMP) Sound Metric Summary
6.128.2.1 SOUND SIGNATURES AT THE MUZZLE
Real sound pressure histories from a 5-shot test acquired with PEW-SOFT™ are shown below. 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 SOCOM556-RC2 with the WARCOMP Closed-Tine Flash Hider are shown in Figure 5a. The sound signatures of Shot 1 and Shot 2 are shown in a smaller time window in Figure 5b. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 6a. In Figure 6b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shot 2, Shot 3, and Shot 4.
Fig 5a. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature
Fig 5b. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature, Short Time Window
Fig 6a. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
Fig 6b. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature, Short Time Window
Just as was noted in PEW Science testing of the SOCOM762-RC2 on a 20-in barrel .308 bolt-action rifle with the WARCOMP mount (6.26) and testing of the SOCOM556-RC2 on a 10.3-in barrel 5.56mm MK18 with the WARCOMP mount (6.52), the M4A1 testing with the WARCOMP mount displays more severe gas momentum accumulation due to a leak out the mount-collar interface. This is visible in both pressure space (Figure 5) and impulse space (Figure 6).
Key differences between the WARCOMP mount leak on the MK18 weapon system and the M4A1 weapon system are:
The leak on the M4A1 weapon system is of lower amplitude and duration. This is due to the lower muzzle blast input pressure from the increased barrel length.
Due to the reduced leak severity of the M4A1 system, along with a greater standoff distance between the mount interface and the weapon operator, hazards to both the operator and bystanders with the WARCOMP mount are reduced on the M4A1, when compared to that on the MK18.
More detailed comparisons between 3-Prong Flash Hider mount and WARCOMP Closed-Tine Flash Hider mount performance on this weapon system, and the MK18 weapon system, are provided in Section 6.128.3.
Operator hazards are still increased with WARCOMP mount use, despite the above factors.
PEW Science Research Note 7: On the M4A1 weapon system, the muzzle sound signature of the SOCOM556-RC2 is more severe when using the WARCOMP mount than the 3-Prong mount, despite the peak pressure amplitude from the WARCOMP mount being lower. It is not only peak pressure amplitude that dictates blast hazard; it is also blast wave shape, phase, and duration. As was noted on the MK18, there is a significant change in gas dynamics with the WARCOMP mount due to early-time gas venting from the mount interface on the M4A1. Direct comparison of the WARCOMP and 3-Prong Flash Hider is provided in Section 6.128.3.
The signatures measured at the shooter’s ear are presented below.
6.128.2.2 SOUND SIGNATURES AT SHOOTER’S EAR
Real sound pressure histories from the same 6-shot test acquired with PEW-SOFT at the shooter’s ear are shown below. Again, 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 primary sound signature pressure histories at the ear for all 6 shots with the SOCOM556-RC2 with the WARCOMP Closed-Tine Flash Hider are shown in Figure 7a. A zoomed-in timescale is displayed in Figure 7b, in the region of peak sound pressure. The real sound impulse (momentum transfer potential) histories at the ear from the same 6-shot test are shown in Figure 8.
Fig 7a. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature
Fig 7b. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Fig 8a. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature
Fig 8b. Surefire SOCOM556-RC2 (WARCOMP) 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature, Short Time Window
The operator is most vulnerable to WARCOMP hazards. As previously observed in 7.62mm bolt-gun WARCOMP testing and 5.56mm MK18 WARCOMP testing, there are significant peaks in both the pressure and impulse regimes in this M4A1 test. There are blast load shock waves at approximately 29 ms (Figure 7b) occurring prior to primary muzzle blast, indicating direct gas venting from the mount area to the shooter’s head position. This gas momentum accumulates at the head as shown in Figure 8.
PEW Science Research Note 8: As discussed in the previous SOCOM762-RC2 and SOCOM556-RC2 reviews with the WARCOMP, this behavior is highly irregular and atypical. This data is a direct empirical indication of silencer mount leakage on a centerfire rifle platform; a hazardous condition for the operator. PEW Science data and analysis indicates that this behavior occurs with the WARCOMP, independent of silencer model and weapon platform. The behavior is mount (WARCOMP) dependent. This level of direct blast propagation can result in direct impingement at the operator’s head position and can subject the operator’s face to high velocity particulate ejecta, independent of the host firearm, and is not related to semi-automatic or automatic weapon system operation. PEW Science recommends PPE be used for all suppressed weapon operation.
It should be noted the increase in hazard from WARCOMP use on the M4A1 is not as severe as with WARCOMP use on the MK18. This reduction in severity increase is a function of the two differences listed in the preceding section: input pressure amplitude and standoff distance.
Detailed comparisons of the 3-prong flash hider and WARCOMP equipped systems are provided below.
6.128.3 SOCOM556-RC2 Mount and Host Weapon Detailed Comparisons
Below, direct comparisons of the measured pressure and impulse waveforms with the two different mounts and weapons used in four tests of the SOCOM556-RC2 are shown. This is a members-only analysis; PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
6.128.3.1 M4A1 and MK18 Host Comparisons
Figure 9a and Figure 9b show first and third shot muzzle overpressure comparisons, respectively, across weapon systems. These comparisons directly illustrate the similarities and differences in gas dynamics at the muzzle due to a change in host weapon with the 556-RC2 silencer mounted with the 3-Prong Flash Hider.
Fig 9a. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO FRP Weapon Pressure Comparison
Fig 9b. Surefire SOCOM556-RC2 (3-Prong FH) 5.56x45mm NATO Shot 3 Weapon Pressure Comparison
Note the extremely similar early time pressure propagation during FRP with the two weapon systems (Figure 9a). While the input pressure is lower from the longer 14.5-in barrel, the output pressure amplitude is extremely similar. This is due to the annular utilization discussed previously in Research Note 1. Note the shorter positive phase duration of the first jet, coupled with higher amplitude of the subsequent jet. The SOCOM556-RC2 is able to somewhat normalize combustion output during FRP due to the higher pressure. Therefore, during the first shot, the signatures of the two weapon systems are the most similar, even though the M4A1 has a longer barrel.
During subsequent shots, however, the annular utilization further diminishes, and the signature becomes more severe with the M4A1 than the MK18 (Figure 9b). The higher amplitude jetting begins to present earlier in time; efficiency is lost. The benefits of the 40% increase in barrel length and its resulting lower input pressure are nullified by the lack of proximal annular utilization.
These trends, in both FRP severity similarity and subsequent shot severity increase with a longer barrel system, are atypical and should not be considered applicable to the behavior of most silencers.
6.128.3.2 WARCOMP and 3-Prong Comparisons Across Hosts
The 3-Prong Flash Hider is non-ported and equipped with “labyrinth seals;” these circumferential machined ridges on the mount help to prevent gasses from escaping the mount interface. PEW Science postulates that the porting is the most significant factor influencing the difference in muzzle blast pressure propagation from the mount interface when using the 3-Prong mount or a WARCOMP mount.
The mount leakage phenomenon that occurs with the WARCOMP was observed in the previous PEW Science testing and analysis of the Surefire SOCOM762-RC2 on a bolt-action rifle, the SOCOM556-RC2 on the MK18, and now the SOCOM556-RC2 on the M4A1.
Despite the different weapons, cartridges, and barrel lengths, the testing and analysis results are consistent. The silencers possess similar locking collars, the ammunition propellant combustion occurs with sufficient pressure to induce blast waves when released to atmosphere suddenly, the secondary blast waves from unburnt propellant from the shorter barrel only contribute further to the issue, the leakage happens in early time so weapon type is inconsequential, and finally, blast waves from the mount interface expand spherically, in three dimensions.
The WARCOMP performance differential on both the MK18 and M4A1 is examined in further detail, below. The waveform differences at the shooter’s ear are extremely significant.
Figure 10a and Figure 10b show first-shot muzzle and shooter’s ear impulse comparisons, respectively. These comparisons directly illustrate the signature difference to the operator between use of the WARCOMP and the 3-prong flash hider equipped system, on both automatic rifles.
Fig 10a. Surefire SOCOM556-RC2 5.56x45mm NATO FRP Mount and Weapon Impulse Comparison
Fig 10b. Surefire SOCOM556-RC2 5.56x45mm NATO Shot 3 Mount and Weapon Impulse Comparison
During FRP, the muzzle signatures from the two weapon systems with the 3-Prong mount (the black lines in Figure 10a) are extremely similar due to the previously discussed annular utilization. And, with the WARCOMP mount (the red lines in the same figure), the gas leak builds similar gas momentum in the free field.
The signatures measured at the operator’s head show some different trends during FRP. While both weapon signatures indicate severe early-time gas momentum accumulation at the operator’s head from the WARCOMP mount leak (the red lines in Figure 10b), the phenomenon is less severe with the M4A1. This is largely due to the increased standoff between the leak location and the operator. The 40% barrel length increase provides this increased standoff.
The 3-Prong signatures at the operators head (the black lines in Figure 10b) display differences, as well. The same standoff distance increase from barrel length lowers the muzzle blast severity at the operator’s head, despite potential ejection port blast increase from longer dwell time of the M4A1 system. This balance was previously discussed in Section 6.128.1.2.
In conclusion:
The Surefire SOCOM556-RC2 does not possess an appreciable performance increase on the M4A1 over that of the MK18.
The WARCOMP mount propagates a high pressure gas leak on every tested system and the operator hazard from that blast load diminishes with greater standoff.
While the second conclusion may have been anticipated by many, the first conclusion is most likely counterintuitive. Gross hazards and behaviors are compared in the following section.
6.128.4 Suppression Rating Comparison (5.56x45mm from the M4A1 and MK18)
Figure 9 presents a comparison of the PEW Science Suppression Rating of the Surefire SOCOM556-RC2 with both the 3-Prong Flash Hider and WARCOMP Closed-Tine Flash Hider mounts on both the M4A1 and MK18 weapon systems. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Figure 11. Suppression Rating Comparisons of the Surefire SOCOM556-RC2 with different mounts and Host Weapons, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 11 presents an overall summary of the postulated hazards to the operator and bystanders when fielding a Surefire SOCOM556-RC2 on the MK18 and M4A1 weapon systems with two different muzzle devices. The Suppression Rating is a holistic parameter that captures human inner ear damage risk potential from a measured impulsive overpressure signature during the entire time regime of weapon operation, including combustion, complete blowdown, and all mechanical operation, including the carrier group returning to battery, in the true free field. The parameter may be used with the dose chart at the beginning of this report. The PEW Science Suppression Rating is a damage risk criterion (DRC), a lower Suppression Rating indicates a higher personnel hazard in the free field - it is not a subjective quantity; it is an objective quantification of hearing damage risk potential.
The following gross conclusions can be made from the above:
The overall suppression performance of the SOCOM556-RC2 with the 3-Prong Flash Hider Mount does not appreciably increase when lengthening the barrel by 40% over than of the 10.3-in MK18. The decrease in operator hazard from muzzle blast standoff outweighs the potential ejection port blast increase on this weapon system and the net result is a shooter’s ear Suppression Rating that is slightly less severe than on the MK18. As further M4A1 research is presented by PEW Science, the performance of other silencers on this weapon system will be compared.
Due to the reduced WARCOMP leak severity on the M4A1 system, along with a greater standoff distance between the mount interface and the weapon operator, hazards to both the operator and bystanders with the WARCOMP mount are reduced on the 14.5-in barrel M4A1, when compared to that on the MK18.
Furthermore, an overall conclusion should be noted: This performance trend with a longer barrel system is atypical and should not be considered applicable to the behavior of most silencers. The Surefire SOCOM556-RC2 was designed for the 10.3-in MK18 weapon system. This report illustrates the potential performance variation characteristics of such a silencer when fielded on a different weapon system. In PEW Science internal laboratory testing, a silencer’s gross signature suppression performance typically increases proportionally to a drop in peak blast pressure input. This performance scaling is a result of proximal silencer geometry. In the case of the SOCOM556-RC2, there is a key design differentiator that prohibits the silencer from providing increased performance on a 14.5-in barrel.
PEW Science Research Note 9: PEW Science postulates it is likely that anecdotal user experiences with Surefire silencers being interpreted as “louder” than competing models have been significantly influenced over the past decade by both the WARCOMP and barrel length performance variations summarized in this report. Because many silencers exhibit increased sound suppression performance on longer barrels, it is possible that the SOCOM556-RC2 may produce a more severe signature than competing models in such scenarios. This performance idiosyncrasy may color user perception, despite the silencer’s high performance on the short-barrel MK18.
As detailed in this report, the Suppression Rating at the shooter’s ear may be significantly influenced by the ejection port signature from an AR15; all other things equal. For details on performance increases that are possible when “tuning” an AR-15 weapon system for a silencer, please see Review 6.111. It is important to note that not all silencers will possess a significant increase in shooter’s ear Suppression Rating from weapon tuning. Signature at the operator’s head is a function of both muzzle and ejection port signatures from the AR-15 weapon system. Specific weapon system parameters will dictate modification efficacy.
Small arm weapon system suppression performance is a spectrum. The PEW Science Suppression Rating and the Silencer Sound Standard help quantify this spectrum for end users and industry, objectively.
6.128.5 Review Summary: Surefire SOCOM556-RC2 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the Surefire SOCOM556-RC2 mounted with the SOCOM 3-Prong flash hider achieved a composite Suppression Rating™ of 35.7 in PEW Science testing. When mounted with the WARCOMP flash hider on the same host weapon and fired with the same ammunition, the SOCOM556-RC2 achieved a composite Suppression Rating of 32.8.
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Surefire SOCOM556-RC2 mounted with the SOCOM 3-Prong flash hider also achieved a composite Suppression Rating™ of 35.7 in PEW Science testing. When mounted with the WARCOMP flash hider on the same host weapon and fired with the same ammunition, the SOCOM556-RC2 achieved a composite Suppression Rating of 29.4.
As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
PEW Science Laboratory Staff Opinion:
The Surefire SOCOM556-RC2 is a full-size 5.56mm machine gun rated rifle silencer that possesses competitive sound signature suppression performance with many silencers on the market, while possessing reduced back pressure compared to some designs. Users should note that full-size 5.56mm rifle silencers are often smaller than their full-size 7.62mm (.30) counterparts. The SOCOM556-RC2 was designed for the 10.3-in MK18 weapon system.
Two mounts (the SOCOM 3-Prong Flash Hider and WARCOMP) were used in the testing of the SOCOM556-RC2 silencer on the M4A1 rifle. Previously, PEW Science tested the same silencer on the MK18 with both mounts, as well as the SOCOM762-RC2 on a bolt action rifle with both mounts. Despite each silencer being tested on different platforms, the testing and analysis results indicate that the use of the WARCOMP is unfavorable for hazard reduction when compared with the 3-Prong Flash Hider mount, regardless of cartridge, barrel length, and silencer.
In this test program, it was concluded that the overall suppression performance of the SOCOM556-RC2 with the 3-Prong Flash Hider Mount does not appreciably increase when lengthening the barrel by 40% over than of the 10.3-in MK18. It was also concluded that due to the reduced WARCOMP leak severity on the M4A1 system, along with a greater standoff distance between the mount interface and the weapon operator, hazards to both the operator and bystanders with the WARCOMP mount are reduced on the 14.5-in barrel M4A1, when compared to that on the MK18.
PEW Science postulates that it is likely that anecdotal user experiences with Surefire silencers being interpreted as “louder” than competing models have been significantly influenced over the past decade by both the WARCOMP and barrel length performance variations summarized in this report. Because many silencers exhibit increased sound suppression performance on longer barrels, it is possible that the SOCOM556-RC2 may produce a more severe signature than competing models in such scenarios. This performance idiosyncrasy may color user perception, despite the silencer’s high performance on the short-barrel MK18.
The Surefire SOCOM556-RC2 was the first silencer evaluated by PEW Science on the standard MK18 weapon system and subsequently included in the public Silencer Sound Standard research pedigree in Sound Signature Review 6.52. Since that publication, the pedigree has grown to include a significant amount of data and analysis, and as a result, the understanding of the suppressed MK18 weapon system by this laboratory, the industry, and the public, has significantly increased. The SOCOM556-RC2 was designed by Surefire to complement the MK18; to perform efficiently in the combustion environment produced by the extremely short 10.3-in 5.56x45mm gun barrel. We encourage the reader to keep this in mind when reviewing the data and analysis in this white paper. The performance of the silencer on the standard M4A1 weapon system is extremely similar to that of its performance on the MK18. In our subjective opinion, this is both a positive and a negative. For a specialized silencer to maintain performance across systems, years after its initial intended development has ceased, is notable. However, a design so dependent upon pressure input for efficacy may limit the utility of the silencer for those end-users pursuing absolute performance on multiple platforms. Furthermore, if the specialized nature of a silencer is not showcased, analyzed, understood, and disseminated to the public, the state of practice stalls. In keeping with the PEW Science mission, the prolific SOCOM556-RC2 is again showcased here in a manner never before seen, this time on the 14.5-in barrel M4A1 mid-length gas platform. As fielding of that weapon system increases, we are pleased at the prospect of the conclusions from this internally-funded research program proliferating and assisting end-users for years to come, as has been the case with our WARCOMP research.
In this review, the Surefire SOCOM556-RC2 performance metrics depend upon suppressing a supersonic centerfire rifle cartridge on a commonly fielded 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.
