SSS.6.213 - Otter Creek Labs OCM5 and OCM6 and the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle (Free Version)

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Otter Creek Labs OCM5 and OCM6 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel

The OCM family of centerfire rifle silencers are designed by Otter Creek Labs and include the OCM5 (5.56 mm standard model) and OCM6 (6 mm higher flow model).  Both OCM silencers are externally similar, aesthetically, to the legacy OPS INC 12th Model silencer and the Allen Engineering AEM5, originally designed by Phil Seberger and manufactured by Ron Allen.  In addition to exterior similarities, both OCM silencers are reflex designs, in that they may be attached to host rifles over-the-barrel using the originally specified thread and taper collar system.  These are the only similarities between the OCM silencers and the legacy OPS INC models.  Technical differences are highlighted below, and in the report body in more detail.

OCM5

The OCM5 is intended for use with the 5.56x45mm NATO cartridge, has a 1.5-inch diameter, and the length of the silencer body is 8.8 inches. The length increases to 9.16 inches when installed on a first-generation OCL OTB muzzle device adapter (duplicating the OPS INC thread and taper interface).  When installed on the host weapon, the resulting silencer length from the barrel shoulder is approximately 6.91 inches.  Therefore, that is the length recorded in the Silencer Sound Standard Rankings database.  The internal design of the OCM5 shares some similarities with an SWR Omega hybrid design baffle array, though it uses straight-cones; a significant departure from the OPS INC dished baffle design later used in Surefire rifle silencers.  The baffle stack is constructed of heat treated stainless steel.  The OCM5 weighs 16 ounces and the first-generation OCL OTB muzzle device weighs 2.5 ounces for a total system weight of 18.5 ounces, as tested.

OCM6

The OCM6 is intended for use with 5.56 NATO, as well as with 6 mm cartridges such as 6 ARC.  The silencer is identical, externally, to the OCM5 other than in its distal vent array and larger exit bore aperture.  The weight of the OCM6 is 16.4 ounces, for a total system weight of 18.9 ounces, as tested.  The internal design of the OCM6 uses a modified multistage hybrid design core derivative of an OCL Infinity baffle array constructed from Inconel alloy; again, a significant departure from the OPS INC design, as well as from the original OCM5. The OCM6 possesses a higher early- and late-time flow rate than the OCM5.

Both the Otter Creek Labs OCM5 and OCM6 can be obtained from Silencer Shop.

The OCM5 may be “upgraded” to the OCM6 by Otter Creek Labs.

Silencer Hazard Maps:

The predicted personnel hazards generated by the tested weapon systems in this report, in the free field, are shown in the adjacent Silencer Hazard Maps. Click or tap the Maps to enlarge. Please reference Silencer Hazard Map Brief 8.1.10 for further details.  The PEW-SOFT HD Blast Hazard Prediction Tool and Hazard Mapper is presented in Report 8.1.1.

Otter Creek Labs OCM5 14.5-in M4A1 AR-15 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data

Otter Creek Labs OCM6 14.5-in M4A1 AR-15 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data

User Caution

As the OCM family of silencers are reflex designs, they occupy length aft of the barrel shoulder when installed. The user is encouraged to exercise due diligence when planning to install an OCM silencer on a host weapon as AR-system handguards and other accessories, such as gas blocks, may interfere. For example, this test program required removing the Daniel Defense handguard from the standard M4A1RIII test host to facilitate installation of the OCM silencer test specimens.  Users are encouraged to contact the silencer manufacturer for exact system component dimensions.

The original OPS INC 12th Model was intended for use on 16-in and 18-in MK12 rifle variants. This test program evaluates the 14.5-in barrel M4 performance of the OCM family for consistency with the existing research pedigree. It is postulated that the testing and analysis results in this program may be somewhat conservative when compared to the performance of the silencer(s) on the MK12 rifle.

PEW Science is an independent private testing laboratory and also hosts the world’s only independent public 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 analysis production for this Sound Signature Review was funded in part by PEW Science Project PEW-OCL-132-001-25. Therefore, data pertaining to the OCM5 and OCM6 in this Sound Signature Review is published with the express written permission of Otter Creek Labs, LLC

The testing and analysis presented in this Sound Signature Review are of the Otter Creek Labs OCM5 and OCM6 on the M4A1 Mid-Gas Automatic AR-15 rifle, chambered in 5.56x45mm NATO with a 14.5-inch barrel with the handguard removed to accommodate installation of the reflex design silencers on the first generation OTB mount. 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.

Report Table of Contents:

  • Section 6.213.1 contains an abbreviated overall summary of Otter Creek Labs OCM rifle silencer performance on the 14.5-in M4.

  • Section 6.213.2 contains OCM5 test results and analysis.

  • Section 6.213.3 contains OCM6 test results and analysis.

  • Section 6.213.4 contains overall Suppression Rating comparisons of the Otter Creek Labs OCM5 and OCM6 with other rifle silencers on the current market on the M4A1 Mid-Gas Rifle, including various configurations of the Whiskey Quebec 5.56 Purged and Non-Purged, Wolfpack Armory Disruptor 556, Otter Creek Labs Infinity, Dillon DRC556, CAT TSWIF, Sylvan Arms SA223TIS, BOE Mod 1, Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, CAT/WB/A1, and Surefire SOCOM556-RC2.

  • Section 6.213.5 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 mounted to the first generation OTB adapter, the the Otter Creek Labs OCM5 achieved a Suppression Rating™ of 42.6 in PEW Science testing.  In the same configuration, the Otter Creek Labs OCM6 achieved a Suppression Rating of 34.1.  

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.

6.213.1 Otter Creek Labs OCM Family 5.56 Automatic Rifle Performance Summary

The PEW Science Silencer Sound Standard includes the 5.56x45mm NATO evaluation of several rifle silencers designed and manufactured by Otter Creek Labs.  Comprehensive performance Rankings are tabulated in Section 7 of the Standard.  This report examines the performance of the specialized reflex models: the OCM5 and OCM6.  The scope of this report contains standard 14.5-in M4A1 weapon system combustion suppression analysis of both silencers installed on the original generation Otter Creek Labs over-the-barrel (OTB) mount which allows the specialized OPS INC-compatible thread and taper interface to be used with standard AR-15 barrels threaded 1/2-28 tpi, given adequate clearance aft of the barrel shoulder.

Figure 1 presents a gross performance comparison of the two silencers on the M4A1 with the unsuppressed case.

Figure 1. Suppression Rating Comparisons of Otter Creek Labs OCM5 and OCM6 Silencers Using PEW-SOFT 5.56x45mm Supersonic M4A1 Test Data and PEW Science Analysis

From the above semiautomatic short-barrel AR-15 rifle performance metrics, it can be concluded that signature suppression levels may increase or decrease in accordance with not only distal blast momentum propagation rate, but also in accordance with other signature components that vary based on silencer internal design.  Furthermore, it is extremely important to note that the early-time flow rate of a silencer may also influence performance, independent of late-time distal momentum control. 

Both the OCM5 and OCM6 are hybrid designs as classified in the research taxonomy. The OCM5, utilizing a straight-cone Omega baffle hybrid derivative, possesses extremely efficient stagnation relief in the tested combustion regime and exhibits significant gross suppression performance, with relatively high back pressure that increases ejection port blast hazards on the standard untuned test host weapon. The OCM6, utilizing an Infinity staged hybrid baffle system derivative, possesses significant early and late time blast load vent paths that reduce system back pressure and lower the ejection port blast hazards to which the operator is subjected.  Forward field gross suppression performance is reduced (ref. Fig. 1, the above Hazard Maps, and 8.1.10).

The detailed 5.56x45mm NATO 14.5-in M4A1 evaluations of the Otter Creek Labs OCM5 and OCM6 silencers follow.

6.213.2 Otter Creek Labs OCM5 Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Otter Creek Labs OCM5 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 public PEW Science testing, research, and development with a membership, here. State-of-the-art public firearm sound signature testing and research conducted by PEW Science is supported by readers like you.

 

Table 1. Otter Creek Labs OCM5 Sound Metric Summary

 

6.213.2.1 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 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 Otter Creek Labs OCM5 are shown in Figure 2a. 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 3a. In Figure 3b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shots 2 and 3.

Fig 2a. Otter Creek Labs OCM5 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature

Fig 2b. Otter Creek Labs OCM5 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature

Figure 3a. Otter Creek Labs OCM5 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature

Figure 3b. Otter Creek Labs OCM5 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature

Historical Technology Note:  The Otter Creek Labs OCM5 is a highly efficient reflex rifle silencer in overall suppression performance.  As discussed in the preceding summary, the OCM5 can be grossly characterized as a straight-cone Omega baffle array derivative, though there are distinct differences between the two technologies, namely the porting structure, baffle throat shapes (not progressive), and and first reflector (blast baffle) geometry.  Regardless of the design differences, it is important to note that the basic premise of the two designs is similar; stagnation relief provided by the vent arrays to annular spaces significantly increases high pressure suppression efficiency.  Furthermore, in both cases, system back pressure is elevated.  This is a well known and recognized performance compromise in Omega baffle array derivatives, historically.  These geometries characterize some of the highest proliferating and highest performing hybrid designs in silencer history, along with the unrelated original OPS INC dished baffle hybrid technologies designed by the late Phil Seberger which were later adopted and incorporated into Surefire rifle silencers.

The OCM5 possesses a robust convex blast baffle and relatively featureless reflex expansion chamber that protrudes aft of the barrel shoulder when installed on the host weapon. This differs from the original OPS INC technology that separates blast loads through early venting into a rear anulus, in somewhat similar fashion to its later non-reflex mount children in the Surefire RC rifle silencer family.  It is likely that some of the first-round-pop (FRP) divergence measured in the above test data results from the OCM5’s first expansion chamber design, though there are additional factors that influence this behavior. Observations from the above test data include the following:

  1. Blast load amplitude is significantly suppressed with relatively long blowdown duration (Fig. 2a).

  2. Bolt carrier group (BCG) return to battery occurs more expediently than typical (Fig. 2a).

  3. Initial internal combustion, precursors, and initial coupled jetting signatures are extremely consistent, shot to shot (Fig. 2b).

  4. Blast load jetting is highly controlled, though elevated during FRP. Post-FRP momentum transfer consistency is strong (Fig. 3).

The observations in (1), (2), and (3) are consistent with high back pressure silencer behavior, in general. The observation in (4) is notable and highlights the high performance potential of the OCM5, FRP notwithstanding.  The high and consistent pure suppression performance of the OCM5 silencer is significant.

PEW Science Research Note 1: It is important to note that not all hybrid designs are “low back pressure.”   Hybrid design silencers are those in which elements of both conventional and high flow rate silencers are used, coupled with other technology variations and staged elements to provide parametrically varied performance attributes.  Although contrasted with so-called Flow-Through technologies in the research taxonomy, hybrid designs predate OSS (HUXWRX) designs.  When stagnation relief is used after primary blast ingress, hybrid design efficiencies are still realized in gross suppression performance, but blast load reflections in early time may greatly elevate the resultant additive blast impulse in close proximity to the barrel muzzle with propagation to the weapon chamber. This is one design attribute that causes the “high back pressure” behavior observed in this subset of hybrid designs.  Hybrid designs span a large range of the market in both brand and performance in different combustion regimes.  There also exist subcategories of this class of silencers that have been shown to demonstrate efficacy in multiple flow regimes.  Discussion of these subcategories is outside the scope of this report.  Other hybrid designs and staged hybrids include those from PTR, CAT, CGS, SilencerCo, Surefire, and others.  For an overview of the three primary classes of rifle silencer designs, the reader is encouraged to review PEW Science Research Supplement 6.169. The Otter Creek Labs OCM6, evaluated in Section 6.213.3 of this report, is a staged hybrid and shares almost no internal design similarities with the OCM5.  It is also a 6 mm silencer, whereas the OCM5 is a dedicated 5.56 mm silencer.

PEW Science Research Note 2: The blast load venting from the OCM5 is extremely controlled. FRP severity may be approximately 60 percent more severe than in subsequent shots, on average, to bystanders adjacent to the weapon system.  It is important to note that the FRP signature severity of the OCM5, though elevated above that in subsequent shots, is still less severe than the average severity from several other competing models.  It is also important to note that the “equivalent” length of the OCM5 silencer is 6.9 inches; the user is encouraged to be mindful of this practical length past the barrel shoulder when comparing performance across silencer models. The visualization tool scatter plot in the Member Rankings Section may assist the reader with such comparisons.

PEW Science Research Note 3: As discussed in the historical technology note above, as presented in the above Hazard Maps, and demonstrated in the calculated shooter’s ear (operator) Suppression Rating, the back pressure generated by the Otter Creek Labs OCM5 is high. The ejection port blast hazards that result from this system back pressure, particularly on the somewhat “over-gassed” standard M4A1RIII test host weapon, may be severe. The user is encouraged to remain mindful of all blast overpressure sources from small arm weapon systems and note both the muzzle and ear Suppression Ratings reported in each analytical test report and the Rankings section of the Silencer Sound Standard. Weapon system tuning may significantly reduce ejection port blast hazards and subsequently increase the effective shooter’s ear Suppression Rating of a high back pressure system. Further examination of the blast load measurements at the operator’s head is provided in Section 6.213.2.2 of this report for PEW Science Members.

PEW Science Research Note 4:  It is extremely important for the reader to understand the Suppression Ratings are computed with free field test data, and are therefore universal when translating the weapon and operator to different environments without reflections.  However, when the environment becomes complex with many reflecting surfaces, performance translation of different systems is not yet possible; sound field shapes and particle velocities result in varied blast wave time-of-arrivals, as well as changes of blast load angles of incidence; these variations change amplitude and phase waveform components.  As a result of these inevitable environmental complexities, user impressions will vary, as both the shooter and bystander.  Nonetheless, hazard reduction efficacy in the free field, as characterized by the Suppression Rating, holds.  The Suppression Rating comparisons are the current state-of-the-art, and the most “apples to apples” sound suppression performance comparisons that currently exist.  Further research is ongoing.

PEW Science Research Note 5: 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 78 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 6: 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 may be 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 entire signatures are used in analysis and Suppression Rating calculations.

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 7: Note that the muzzle Suppression Rating of the Otter Creek Labs OCM5 is 42.5 and the at-ear Suppression Rating is 17.5; different zones on the Suppression Rating Dose Chart. The higher back pressure of the OCM5 contributes to severe ejection port blast signature when compared to lower back pressure silencers on the standard untuned M4A1 weapon system. System tuning (adjustable gas block or heavier buffer mass) may be required to optimized the user’s particular weapon system.  Weapon tuning may influence hazard reduction efficacy, and is outside the scope of this study.

The signatures measured at the shooter’s ear with the OCM5 are presented and analyzed in the full member version of this report.

The evaluation in this section covered the performance of the OCM5 silencer that has low early-time flow rate and restricted / low late-time flow rate. By redesigning the silencer’s core and slightly increasing the bore size to accommodate 6 mm projectiles, Otter Creek Labs created the OCM6 silencer that possesses elevated early and late-time flow rate; the blast load is able vent from the blast chamber and progressively in different stages of the core to annular space, with some paths that terminate in a distal vent array. Test results and analysis of the OCM6 on the same weapon system are presented in the following section.

6.213.3 Otter Creek Labs OCM6 Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Otter Creek Labs OCM6 is shown in Table 2. 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 public PEW Science testing, research, and development with a membership, here. State-of-the-art public firearm sound signature testing and research conducted by PEW Science is supported by readers like you.

 

Table 2. Otter Creek Labs OCM6 Sound Metric Summary

 

6.213.3.1 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 Otter Creek Labs Infinity with vented 5.56 end cap are shown in Figure 6a. The sound signatures of Shot 1 and Shot 2 are shown in Figure 6b, in early time. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 7a. In Figure 7b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shots 2 and 3.

Fig 6a. Otter Creek Labs OCM6 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature

Fig 6b. Otter Creek Labs OCM6 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature

Fig 7a. Otter Creek Labs OCM6 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature

Fig 7b. Otter Creek Labs OCM6 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature

Unlike the OCM5, the OCM6 is a 6 mm silencer and utilizes a modified multi-stage Infinity baffle core intended to increase early- and late-time flow rate of the system to reduce back pressure and therefore reduce adverse ejection port blast hazards to the weapon operator. Another feature of the OCM6 design, contrasted with the previously evaluated OCM5, is a distal vent array.  The OCM6 possesses eight distal vents in a radial pattern around the exit aperture of the silencer end cap. These vents relieve pressure from the core annulus.

The same exterior dimensions and mounting system are used with both OCM5 and OCM6 silencers. However, the core change in the OCM6 results in significant behavioral changes in weapon dynamics, blast load propagation, and personnel hazard reduction throughout the pressure field.  The following major differences are noted when examining the above test data:

  1. Higher free field blast overpressure amplitude is noted with lower BCG velocity (Fig. 6a).

  2. Early precursor and coupled jet consistency remains, but initial primary jetting is accompanied by a pronounced increase in positive phase duration (Fig. 6b).  Latent jetting remains controlled.

  3. FRP divergence occurs but relative severity compared with that of subsequent shots is significantly reduced (Fig. 7) compared to the previously evaluated OCM5. Post-FRP throttle is consistent and controlled.

  4. Gross momentum transfer is elevated in both accumulate rate and amplitude (Fig. 7).

As observed in (1), (2), and (4), the OCM6 exhibits completely different behavior than the OCM5; the OCM6 has a higher flow rate (lower back pressure), vents more expediently to atmosphere, and the hazard field to bystanders is higher risk.  This is reflected in the muzzle (bystander) Suppression Rating of the silencer dropping from 42.5 (OCM5) to 33.5 (OCM6).  This is almost a full category drop in bystander protection and should be considered significant.  As observed in (3), post-FRP relative performance consistency is  largely maintained.

PEW Science Research Note 9: Though the bystander hazard reduction of the OCM6 is less robust than with the OCM5, the operator hazard reduction is improved. This specific performance increase results directly from the increased early- and late-time flow rate in the OCM6 core, which reduces system backpressure and therefore reduces the severity of blast overpressure venting from the weapon breech and gas tube orifice at the time of bolt unlocking.  It is likely that the nominal amount of overbore also contributes to these benefits on this weapon system.  This phenomenon is discussed further in Section 6.213.3.2.

PEW Science Research Note 10: Though the OCM6 silencer produces a more severe forward hazard field than the OCM5, the FRP severity of the OCM6, relative to that of subsequent shots, is reduced. This phenomenon is partially due to the increased hazard field, but is also driven by the significantly more advanced core geometry of the OCM6.  It is important to note that even though the OCM6 has lower relative FRP than the OCM5, the OCM6 will produce a more severe bystander signature than the OCM5 regardless of the shot sequence, when compared in absolute terms. The OCM6 is unable to reach the muzzle suppression performance of the OCM5, in general.  In practical terms, this means that OCM5 users will most likely discern FRP differential, but the FRP will be less severe than any shot fired from an OCM6, all other things equal, on this weapon system.

By utilizing an Infinity core derivative, the OCM6 is most likely the most advanced hybrid design version of the OPS INC “military clone” family of rifle silencers. The suppression performance on a standard untuned weapon system is more “balanced” with the OCM6 than it is with the OCM5 silencer.

PEW Science Research Note 11: To accompany the information in Research Note 1 of this report, in the context of both the OCM5 and OCM6, it is worth listing various other technologies in the hybrid design taxonomy. Differential flow rates in early and late-time are common characteristics of advanced hybrid designs in which elements of high flow rate designs are combined with more traditional geometries to throttle the rate of combustion gas propagation late enough in the time regime so weapon operation is influenced to a lower degree.  Other examples of hybrid technologies and hybrid designs examined in the Standard research pedigree include (but are not limited to):

  1. Otter Creek Labs Infinity Technology - Infinity 7.62 (6.178)

  2. CGS Hyperion Technology - Hyperion (6.27), Hyperion K (6.28), Helios QD (6.13), SCI-SIX (6.101)

  3. Surefire Total Signature Reduction - SOCOM556-RC2 (6.128), SOCOM762-RC2 (6.26), SOCOM556-RC3 (6.151), SOCOM-556-MINI2 (6.144)

  4. CAT SURGE BYPASS - CAT ODB (6.120), CAT WB (6.130), CAT TSWIF (6.193), CAT CACM (6.203)

  5. Liberty Precision Machine Tech - Torch (6.126)

  6. SilencerCo LBP - Velos LBP (6.134)

  7. PTR Purposely Induced Porosity (PIP) - VENT 3 (6.135), VENT Spiritus 556i (6.176), Dillon DRC556 (6.194)

  8. KAC Pressure Reduction Technology (PRT) - KAC 556 QDC/CRS-PRT (6.156), KAC 556 QDC/MCQ-PRT (6.156)

  9. FOR Systems Tech - Monarch 7.62 (6.155) and Monarch Recce (6.195)

  10. Sig Sauer Forward Flux - SLH300Ti (6.107)

Again, the above are classified as hybrid designs in the PEW Science research taxonomy.  None of the above technologies or silencers are “Flow-Through” designs. That technology is only available from HUXWRX, and its principles of operation differ significantly from all of the above. Although some of the above silencers may be marketed as “Flow-Through” silencers by dealers and distributors that sell products, the physical mechanisms and performance differentials between all of the technologies are significant.  The reader is highly encouraged to examine the in-depth laboratory testing and analysis of HUXWRX systems for a detailed description of pertinent behavioral factors.  For example, when distal gas velocity increases significantly, as it does in a true Flow-Through design, there are consequences to the sound field that may induce unfavorable frequency components and reflection phenomena. The Research Caution at the beginning of this linked FLOW 556 Ti test report elaborates on this phenomenon, with additional research references available.

Signature analysis of test data acquired near the operator’s head with the Otter Creek Labs OCM6 is presented the full member version of this report.

Two OCM silencer configurations have been examined in detail and personnel hazard risk factors examined.  Below, the two OCM configurations are compared with other silencers on the standard untuned M4 rifle.

6.213.4 Suppression Rating Comparison (5.56x45mm from the M4A1)

Figure 10 presents a comparison of the PEW Science Suppression Ratings of the Otter Creek Labs OCM5 and OCM6 reflex silencers, with those of several other silencers on the M4A1 weapon system. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127.

Figure 10. Suppression Rating Comparisons of the Otter Creek Labs OCM5, OCM6, Whiskey Quebec 5.56 Purged and Non-Purged, Wolfpack Armory Disruptor 556, Infinity, Dillon DRC556, CAT TSWIF, Sylvan Arms SA223TIS, BOE Mod 1, Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, Surefire SOCOM556-MIN2, CAT WB, and SOCOM556-RC2 with different mounts, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis

Figure 10 presents an overall summary of the postulated hazards to the operator and bystanders when fielding the Otter Creek Labs OCM5 and OCM6 on the M4A1 weapon system with the first generation OTB mount (shown in red).  Note that the M4A1 handguard was removed in the OCM5 and OCM6 tests to accommodate the reflex portion of the silencers.  Data is also presented for the fielding cases of the Battle Born Supply Co. Whiskey Quebec 5.56 series (6.206), Wolfpack Armory Disruptor 5.56 (6.199), Otter Creek Labs Infinity (6.196), Dillon DRC556 (6.194), CAT TSWIF (6.193), Sylvan Arms SA223TIS (6.187),  BOE Mod 1 (6.183), Echo Zulu Defense X1R556-Ti (6.181), PTR VENT Spiritus 556i (6.176), HUXWRX FLOW 556 Ti (6.168), Surefire SOCOM556-RC2 (6.128), SOCOM556-MINI2 (6.144), and KAC QDC PRT units (6.156) on different muzzle devices, along with fielding of the CAT WB (6.130).  Hazards are expressed with the Suppression Rating; a holistic parameter that captures human inner ear damage risk potential from a measured impulsive complex 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.  Due to its true free field test data origin and complete waveform analytical calculation basis, it is the only known universal suppressed weapon system signature comparison metric available.

The following gross conclusions can be made from the above:

  1. The Otter Creek Labs OCM5 produces free field bystander hazard reduction on par with that of high performing designs like the Dillon DRC556 (6.194), BOE Mod 1 (6.183)), and PTR VENT Spiritus 556i (6.176).

  2. The 6 mm bore higher flow rate Otter Creek Labs OCM6 produces free field bystander hazard reduction on par with that of the Surefire SOCOM556-RC2 (6.128), Whiskey Quebec 5.56 (6.206), and Otter Creek Labs Infinity with vented 7.62 end cap (6.196).

  3. The free field operator (shooter) hazard reduction of the OCM5 is lower than typical on the untuned M4A1 rifle, and similar in severity to the SOCOM556-MINI2 with a WARCOMP mount (6.144), the small KAC QDC/MCQ-PRT with MAMS mount (6.156), and high back pressure silencers like the Sylvan Arms SA223TIS (6.187) and Wolfpack Armory Disruptor 5.56 (6.199).  Weapon tuning is advised.

  4. The operator hazard reduction of the OCM6 is higher than that of the OCM5 and is more similar to silencers on this weapon system like the CAT TSWIF (6.193) and the Otter Creek Labs Infinity with solid 5.56 end cap (6.196).

PEW Science Research Note 13: The muzzle Suppression Rating of the Otter Creek Labs OCM5 is in the top 4 of the PEW Science laboratory M4A1 Rankings, and the shooter’s ear Suppression Rating of the OCM6, characterizing operator risk in the free field from the low back pressure OCM variant, almost enters the current top 10 in the Rankings.  Overall, the OCM silencer family provides “military clone” OPS INC silencer enthusiasts modern design options that may be readily installed on typical standard threaded AR-15 rifle barrels, and provides these users a choice of high overall suppression performance or reduced back pressure with 6 mm cartridge suppression capability.  Regardless of the user’s choice of these types of historical homage reflex silencer designs, weapon tuning is highly recommended to optimize operator hazard reduction.

As detailed in this report, 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.

6.213.5 Review Summary: Otter Creek Labs OCM5 and OCM6 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 mounted to the first generation OTB adapter, the the Otter Creek Labs OCM5 achieved a Suppression Rating™ of 42.6 in PEW Science testing.  In the same configuration, the Otter Creek Labs OCM6 achieved a Suppression Rating of 34.1.  

As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.

PEW Science Laboratory Staff Opinion:

The Otter Creek Labs OCM5 and OCM6 rifle silencers are modern high performance reflex models sharing external aesthetic similarities with the historic OPS INC reflex silencers designed by the late Phil Seberger and manufactured by Ron Allen.  Internally, the 5.56 mm bore OCM5 uses a highly efficient hybrid core design to provide extreme pure suppression performance, at the expense of higher back pressure.  The 6 mm bore OCM6 uses a more modern Infinity core derivative and exhibits lower back pressure with a decrease in pure suppression performance compared to the OCM5.  Both silencers may be easily mounted to standard AR-15 barrels using over-the-barrel (OTB) mounts from Otter Creek Labs, as long as there is adequate clearance aft of the barrel shoulder.  These silencers provide “military clone” OPS INC silencer enthusiasts modern design options.

The OCM5 can be grossly characterized as a straight-cone Omega baffle array derivative, though there are distinct differences between the two technologies, namely the porting structure, baffle throat shapes (not progressive), and and first reflector (blast baffle) geometry.  Regardless of the design differences, it is important to note that the basic premise of the two designs is similar; stagnation relief provided by the vent arrays to annular spaces significantly increases high pressure suppression efficiency.  Furthermore, in both cases, system back pressure is elevated.  This is a well known and recognized performance compromise in Omega baffle array derivatives, historically.  These geometries characterize some of the highest proliferating and highest performing hybrid designs in silencer history, along with the unrelated original OPS INC dished baffle hybrid technologies designed by the late Phil Seberger which were later adopted and incorporated into Surefire rifle silencers.

The back pressure generated by the Otter Creek Labs OCM5 is high. The ejection port blast hazards that result from this system back pressure, particularly on the somewhat “over-gassed” standard M4A1RIII test host weapon, may be severe. The user is encouraged to remain mindful of all blast overpressure sources from small arm weapon systems and note both the muzzle and ear Suppression Ratings reported in each analytical test report and the Rankings section of the Silencer Sound Standard. Weapon system tuning may significantly reduce ejection port blast hazards and subsequently increase the effective shooter’s ear Suppression Rating of a high back pressure system.

Unlike the OCM5, the OCM6 is a 6 mm silencer and utilizes a modified multi-stage Infinity baffle core intended to increase early- and late-time flow rate of the system to reduce back pressure and therefore reduce adverse ejection port blast hazards to the weapon operator. Another feature of the OCM6 design, contrasted with the previously evaluated OCM5, is a distal vent array.  The OCM6 possesses eight distal vents in a radial pattern around the exit aperture of the silencer end cap. These vents relieve pressure from the core annulus.

Though the bystander hazard reduction of the OCM6 is less robust than with the OCM5, the operator hazard reduction is improved. This specific performance increase results directly from the increased early- and late-time flow rate in the OCM6 core, which reduces system backpressure and therefore reduces the severity of blast overpressure venting from the weapon breech and gas tube orifice at the time of bolt unlocking.  It is likely that the nominal amount of overbore also contributes to these benefits on this weapon system. 

The Otter Creek Labs over-the-barrel (OTB) mounting system is extremely simply to use; it may be installed onto a standard AR-15 rifle barrel and the included rear taper interfaces with the OCM family of silencers as well as with legacy OPS INC models, providing expedient adaptability of this family of reflex silencers to existing weapon systems that would otherwise require barrel modification.  The user is encouraged to exercise due diligence when planning to install an OCM silencer on a host weapon as AR-system handguards and other accessories, such as gas blocks, may interfere. For example, this test program required removing the Daniel Defense handguard from the standard M4A1RIII test host to facilitate installation of the OCM silencer test specimens.  Users are encouraged to contact the silencer manufacturer for exact system component dimensions.

In this review, the Otter Creek Labs OCM5 and OCM6 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.