SSS.6.179 - Otter Creek Labs Infinity and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)

/

Otter Creek Labs Infinity on the MK18 5.56x45mm AR15 with 10.3-in Barrel

The Infinity is a 30 caliber centerfire rifle silencer designed by Otter Creek Labs.  The Infinity is intended to suppress many cartridges with projectiles appropriately sized to travel through the bore, and may be used with severe firing schedules. It has a 1.73-inch diameter and is 6.6 inches long without a mount.  The silencer does not include any mounts; the proximal end of the Infinity is threaded 1.375-24 tpi to accommodate “HUB” compatible mounting systems.  The silencer body is 3D-printed from Inconel 718 alloy and the retail package includes multiple heat-treated stainless steel end caps that change system behavior.  The user may choose to install different end caps to achieve varying flow states appropriate for the combustion dynamics of the chosen cartridge and weapon system.  With an end cap installed, the silencer weighs 20 ounces and with a Rearden titanium direct-thread mount, weighs 20.8 ounces and is 6.8 inches long, as tested.  The Otter Creek Labs Infinity can be obtained from Silencer Shop.

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-103-001-24. Therefore, data pertaining to the Infinity 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 Infinity with three different end caps on the MK18 Automatic AR15 rifle 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.

Otter Creek Labs Infinity testing and analysis with bolt-action 7.62x51mm NATO is documented here.

  • Section 6.179.1 contains an abbreviated overall summary of Otter Creek Labs Polonium and Infinity rifle silencer performance on the standard 5.56 MK18.  Contextual comparisons are provided for the Polonium, Polonium-K, Polonium-30, and all tested configurations of the Infinity.

  • Section 6.179.2 contains Infinity Solid 5.56 End Cap test results and analysis.

  • Section 6.179.3 contains Infinity Vented 5.56 End Cap test results and analysis.

  • Section 6.179.4 contains Infinity Vented 7.62 End Cap test results and analysis.

  • Section 6.179.5 contains overall Suppression Rating comparisons of the Infinity with 3 end caps with dedicated 223 and 30 caliber silencers on the current market, including the PTR VENT Spiritus 556i, LMT AT ION LT, HUXWRX FLOW 556 Ti, Off Grid Operator Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, Surefire SOCOM556-RC3, Otter Creek Labs Polonium-30, AAC M4-2000 Mod 08, PTR VENT 3, SilencerCo Velos LBP, BOSS Guillotine, CAT WB, PWS BDE 556, CAT ODB, Aero Precision Lahar-30L, Lahar-30, HUXWRX FLOW 762 Ti, Maxim Defense DSX, Thunder Beast Dominus, KAC 5.56 QDC, CGS SCI-SIX, 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 6.179.6 contains an article summary and PEW Science laboratory staff opinions.

Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193 with the solid 5.56 end cap, the the Otter Creek Labs Infinity achieved a Suppression Rating™ of 40.2 in PEW Science testing.  With the vented 5.56 end cap, the Otter Creek Labs Infinity achieved a Suppression Rating of 33.5.  With the vented 7.62 end cap, the Otter Creek Labs Infinity achieved a Suppression Rating of 28.9.

7.62x51mm NATO bolt-action rifle test results and analysis with the Otter Creek Labs Infinity is provided in report 6.178.

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.

6.179.1 Otter Creek Labs Rifle Silencer 5.56 Automatic Rifle Performance Summary

The PEW Science Silencer Sound Standard public research pedigree includes the 5.56x45mm NATO evaluation of four rifle silencers designed and manufactured by Otter Creek Labs.  Comprehensive performance Rankings are tabulated in Section 7 of the Standard.  The scope of this report contains standard MK18 reciprocating weapon system combustion suppression analysis.  To that end, Figure 1 presents a performance comparison of six Otter Creek Labs rifle silencer configurations currently evaluated.  The configurations include:

  • 6.179 - Infinity (7.62 mm vented end cap): a hybrid design 30 caliber silencer with ancillary axial and annular venting at the distal end, with an over-bored 7.62-sized primary orifice.

  • 6.95 - Polonium-K: a conventional cone design 5.56 silencer (compact-size).

  • 6.179 - Infinity (5.56 mm vented end cap): a hybrid design 30 caliber silencer with ancillary axial and annular venting at the distal end, with a 5.56-sized primary orifice.

  • 6.143 - Polonium-30: a conventional cone design 30 caliber silencer (compact-size).

  • 6.179 - Infinity (5.56 mm solid end cap): a hybrid design 30 caliber silencer with only axial bore venting at the distal end.

  • 6.75 - Polonium: a conventional cone design 5.56 silencer (full-size).

The silencers are presented in order, in accordance with their distal blast momentum propagation rate, from least restrictive to most restrictive.  The rate of distal external blast momentum accumulation is quantified by the calculated PEW Science Omega Metric (6.40).

Figure 1. Suppression Rating Comparisons of Otter Creek Labs Rifle Silencers Using PEW-SOFT 5.56x45mm Supersonic 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.  For example, the Polonium-K (6.95) may have a lower rate of distal blast momentum propagation (lower Omega Metric) than the Infinity with its solid 5.56 end cap, but the Infinity most certainly has a higher early-time flow rate than the Polonium-K.  This may result in varying levels of semiautomatic weapon platform performance comparison.  For further details on such performance factors, the reader is encouraged to examine the performance comparisons in this report, the previous 7.62x51mm bolt-action performance evaluation report from this test program (6.178), and the full PEW Science performance Rankings contained in Section 7 of the Silencer Sound Standard.

The 5.56x45mm NATO 10.3-in MK18 evaluation of the Otter Creek Labs Infinity with 5.56 solid, 5.56 vented, and 7.62 vented end caps follows.

6.179.2 Otter Creek Labs Infinity Solid 5.56 End Cap Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Otter Creek Labs Infinity with solid 5.56 end cap 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 Infinity Solid 5.56 End Cap Sound Metric Summary

 

6.179.2.1 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 Infinity with solid 5.56 end cap 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 Infinity Solid 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature

Fig 2b. Otter Creek Labs Infinity Solid 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature

Figure 3a. Otter Creek Labs Infinity Solid 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

Figure 3b. Otter Creek Labs Infinity Solid 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

As discussed in the preceding summary and in the 7.62x51mm NATO bolt-action Infinity analytical report (6.178), the Otter Creek Labs Infinity is a 30 caliber rifle silencer that is classified as a hybrid design in the PEW Science research taxonomy.  More specifically, the Infinity is classified as a staged hybrid.  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. Such attributes include the ability to reduce early-time shock reflections while significantly altering the rate of proximal and distal venting. These silencers may allow for minimal reciprocating weapon functional influence, while at the same time significantly suppressing signature to the operator and bystanders. 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 Infinity hybrid design is characterized by the following physical design attributes:

  • Early venting in the first expansion (blast) chamber prevents excessive blast load impulse accumulation in early time.

  • Clearing off of the first reflector (blast baffle) occurs through venting on both the convex surface and boundary walls.

  • Multiple stages are utilized; high pressure baffle geometry in the first stage, lower pressure geometry in the second stage, and varied alternate flow path geometries that are utilized differently in accordance with user choice of end cap.

PEW Science Research Note 1: The Infinity represents a large step forward in the Otter Creek Labs design pedigree.  When fitted with the solid 5.56 end cap, the Otter Creek Labs Infinity functions as a 30 caliber rifle silencer with a high early-time flow rate and a restricted late-time flow rate. This performance is demonstrated by the following characteristics shown in the above test data:

  1. Relatively longer blowdown duration (Fig. 2a).

  2. Lack of decoupled ground reflection, consistent with (1).

  3. Relatively short initial positive phase blast load duration with coincident rarefaction, throttled externally in early time (Fig. 2b).

  4. Blast pressures reach maxima post-initial jetting (Fig. 2b).

  5. Relatively typical duration rise to maximum positive phase blast impulse for the silencer’s size (Fig. 3a).

This gross behavior is extremely similar to that observed on the .308 bolt-action rifle in report 6.178. However, a primary difference in the 7.62 NATO and 5.56 NATO performance of the infinity is how the silencer deals with combustion gas volume and jet diameter.  The Infinity is much more efficient in 5.56 suppression than it is in the suppression of 7.62 NATO.  This is particularly the case in first-round-pop (FRP) control, in which the relative severity on the MK18 from the Infinity is significantly reduced compared to on the 20-in barrel bolt-action .308 rifle.  The early-time blast load venting in the first expansion chamber of the Infinity is well-suited to controlling 5.56 NATO jetting.  For all intents and purposes, users are likely to observe that the Infinity may be considered an advanced performance 5.56 rifle silencer that can also suppress 7.62mm cartridges at typical levels.  

PEW Science Research Note 2: To be clear, the solid 5.56 end cap configuration of the Otter Creek Labs Infinity is the most restrictive configuration of the silencer. Although the system still possesses a high early-time flow rate from expansion chamber venting to multiple stages, downstream orifice restriction does result in an elevated Omega Metric and compromise of operator protection. The exceptional muzzle (bystander) Suppression Rating of 40.0 is accompanied by the lower shooter’s ear (operator) Suppression Rating of 23.4. When such a wide differential in bystander and operator Suppression Rating is noted, the user should immediately examine the reasons as to why such divergence occurs.  In the case of the Infinity, its early-time flow rate is not high enough to forgo the required accompaniment of less downstream restriction; the Infinity’s hybrid design requires ancillary downstream venting to significantly lower ejection port blast to the weapon operator.  This is in contrast to some other hybrid designs that natively include such venting without compromising momentum control, such as technologies from PTR (Purposely Induced Porosity, or “PIP”) and CAT (Surge Bypass, SNIPER2, SB-SHOCK).

It is important to note that even with downstream restriction, the solid 5.56 end cap configuration of the Otter Creek Labs Infinity outperforms the Otter Creek Labs Polonium (6.75) in most signature suppression metrics. With its staged hybrid design, the Infinity is able to surpass the Polonium in overall pressure field suppression while at the same time providing enough early-time venting to reduce the propensity for severe blast load reflection into the weapon bore. The effective “backpressure” of the Infinity is lower than that of the Polonium, regardless of end cap choice. And, accordingly, the solid 5.56 end cap configuration of the Infinity also surpasses the MK18 operator protection of the Otter Creek Labs Polonium-K (6.95); a silencer with lower back pressure than the full-size Polonium. It is extremely important to note that the reduction in back pressure between the Polonium and Polonium-K is driven only by downstream restriction from the use of less baffles; an isolated Omega Metric drop with a constant Alpha parameter from identical early-time blast load impulse accumulation in the first expansion chamber. The Otter Creek Labs Infinity lowers Alpha while allowing the user to vary Omega through the use of end cap choice.  Without early-time venting, semiautomatic rifle silencers may never achieve requisite performance efficacy.  For this reason, the Infinity should be considered a next generation silencer relative to the previous models offered from Otter Creek Labs.

PEW Science Research Note 3: 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. CGS Hyperion Technology - Hyperion (6.27), Hyperion K (6.28), Helios QD (6.13), SCI-SIX (6.101)

  2. Surefire Total Signature Reduction - SOCOM556-RC2 (6.52), SOCOM762-RC2 (6.26), SOCOM556-RC3 (6.151), SOCOM-556-MINI2 (6.144)

  3. CAT SURGE BYPASS - CAT ODB (6.120), CAT WB (6.129)

  4. Liberty Precision Machine Tech - Torch (6.126)

  5. SilencerCo LBP - Velos LBP (6.134)

  6. PTR Purposely Induced Porosity (PIP) - VENT 3 (6.135), VENT Spiritus 556i (6.175)

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

  8. FOR Systems Tech - Monarch 7.62 (6.155)

  9. 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 FLOW 556 Ti test report elaborates on this phenomenon, with additional research references available.

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 95 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 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 7: Note that the muzzle Suppression Rating of the Otter Creek Labs Infinity with solid 5.56 end cap is 40.0 and the at-ear Suppression Rating is 23.4; different zones on the Suppression Rating Dose Chart. The lower back pressure of the Infinity with solid 5.56 end cap does contribute to a less severe ejection port blast signature than silencers like the Otter Creek Labs Polonium or Polonium-K, but the back pressure is not low enough to substantially reduce the ejection port blast loads to the shooter on the standard MK18 weapon system. An end cap change may be required for the user’s particular weapon system.  And, accordingly, weapon tuning may influence hazard reduction efficacy, and is outside the scope of this study.

The signatures measured at the shooter’s ear are presented and analyzed in the full Member Version of this report.

The evaluation in this section covered the performance of the silencer with high early-time flow rate and restricted / relatively low late-time flow rate. By changing the end cap to the 5.56 vented configuration, late-time flow rate is elevated; the blast load is able to further vent from the primary bore and also now vent from the annular space. Test results and analysis of that configuration are presented in the following section.

6.179.3 Otter Creek Labs Infinity Vented 5.56 End Cap Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Otter Creek Labs Infinity with vented 5.56 end cap is shown in Table 2. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all.  Again, 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 Infinity Vented 5.56 End Cap Sound Metric Summary

 

6.179.3.1 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 Infinity Vented 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature

Fig 6b. Otter Creek Labs Infinity Vented 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature

Fig 7a. Otter Creek Labs Infinity Vented 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

Fig 7b. Otter Creek Labs Infinity Vented 5.56 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

As was observed in previous Infinity 7.62 NATO testing with a vented end cap change, when fitted with the vented 5,56 end cap, the performance of the Otter Creek Labs Infinity changes significantly.  The varying stages of the silencer are utilized differently, and blast loads are now vented from both annular space and additional primary axial volume.  This results in the following behavioral changes, observed in the above data plots:

  1. More expedient blowdown, with ground reflection beginning to decouple (Fig. 6a).

  2. More expedient and higher amplitude initial jetting with a more defined initial positive phase, signifying greater momentum propagation (Fig. 6b).

  3. Faster rise to maximum positive phase blast load impulse (lower Omega Metric) in all shots (Fig. 7a).

  4. Uncontrolled erratic blast load momentum propagation in some shots, post-FRP (see Shot 2, Fig. 6b and Fig. 7).

As previously discussed in the 7.62 NATO analysis, observation (4), above, is relatively common when excess blast load vent area is introduced into a primary flow path.  It is likely that this adverse erratic combustion propagation originates from the ancillary venting of the primary bore.

PEW Science Research Note 9:  The silencer has now changed function; the Infinity with a vented end cap is no longer a low-alpha, moderate-omega hybrid- it has been transformed into a low-alpha, low-omega hybrid.  While many positive attributes of its hybrid design are maintained, higher gas velocity and momentum propagation begin to push its performance envelope into a regime in which both bystander and operator risk may be compromised. Overall pressure field shape is also changed due to particle velocity gradients.  For example, note that the muzzle (bystander) Suppression Rating has dropped and now matches that of the previous generation Otter Creek Labs Polonium-K (6.95).  However, the shooter’s ear (operator) Suppression Rating increases to offer more operator protection than the solid 5.56 end cap Infinity configuration, and half a category more protection than the Polonium-K.  This is the result of more extreme distal blast momentum propagation, but lower Omega Metric that drops back pressure.  The elevation of late-time flow rate results in less ejection port blast hazard to the system operator.

This end cap change, and subsequent flow rate change resulting from different utilization of primary axial bore and annular blast load propagation, results in standard untuned 5.56 MK18 performance metrics that move the Infinity hybrid design into contention with systems such as the vented Liberty Precision Machine Torch (6.126).  The 5.56 vented Infinity matches the operator protection (shooter’s ear Suppression Rating) of the vented Torch, while exceeding the bystander protection (muzzle Suppression Rating) of the vented Torch by half a performance category.  This is a significant achievement.

Notably, the Otter Creek Labs Infinity with the vented 5.56 end cap almost achieves the free field operator protection of the HUXWRX HX-QD 556 (6.54), and again, exceeds the free field bystander protection by almost half a category. In addition to this performance achievement, the Infinity’s hybrid design accomplishes this with significantly more distal blast momentum propagation control. The lower particle velocity from the Infinity, in contrast with the pure Flow-Through design of the HX-QD, will enable operators and bystanders to be more protected in a wider range of environments than with the HUXWRX silencer, objectively.  When compared with the vented configuration of the CGS Helios QD (6.66), the vented 5.56 end cap Infinity configuration significantly exceeds its performance.

When compared with advanced hybrid designs like the CAT WB (6.129), the vented 5.56 end cap configuration of the Otter Creek Labs Infinity is competitive, but does fall short in raw performance, in consistency, and in size; the Infinity is much larger than the WB.  Nonetheless, the performance of the Infinity in this regard is notable.  When compared to the 30 caliber CAT ODB (6.120) and the 5.56 PTR VENT Spiritus 556i (6.175), the vented Otter Creek Labs Infinity is eclipsed in performance.

Signature analysis of test data acquired near the operator’s head is presented in the full report.

The evaluation in this section covered the performance of the silencer with high early-time flow rate and elevated late-time flow rate. By changing the end cap from the 5.56 vented configuration to the 7.62 vented configuration, late-time flow rate is even further elevated; the blast load is now able to significantly vent from the primary bore in addition to the ancillary venting from annular space. Test results and analysis of that final configuration are presented in the following section.

6.179.4 Otter Creek Labs Infinity Vented 5.56 End Cap Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Otter Creek Labs Infinity with vented 7.62 end cap is shown in Table 3. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. Once again, 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 3. Otter Creek Labs Infinity Vented 7.62 End Cap Sound Metric Summary

 

6.179.4.1 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 7.62 end cap are shown in Figure 10a. The sound signatures of Shot 1, Shot 2, and Shot 3 are shown in Figure 10b, in early time. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 11a. In Figure 11b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shots 2 and 3.

Fig 10a. Otter Creek Labs Infinity Vented 7.62 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature

Fig 10b. Otter Creek Labs Infinity Vented 7.62 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature

Fig 11a. Otter Creek Labs Infinity Vented 7.62 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

Fig 11b. Otter Creek Labs Infinity Vented 7.62 End Cap 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature

As was observed above in the vented 5.56 end cap testing, and in the vented 7.62 end cap testing showcased in the 7.62 NATO evaluation, when fitted with the vented 7.62 end cap, the 5.56 MK18 performance of the Otter Creek Labs Infinity changes significantly. In addition to annular venting and ancillary axial bore venting, the primary bore vent itself is now enlarged. This is the highest vent area configuration of the Infinity and provides the highest distal flow rate possible.  And, as discussed in the PEW Science Silencer Sound Standard research pedigree ad nauseum, over-bore as a mechanism of flow rate increase (back pressure reduction) is seldom efficient.  As analytical history has shown, this is demonstrated once again in the above data plots.  Observe the severe jetting manifesting as high amplitude blast overpressure in Figure 10.  Furthermore, observe the significantly prolonged positive phase blast load impulse accumulation from the severe jetting displayed in Figure 11.

PEW Science Research Note 11: The over-bore from the vented 7.62 end cap configuration of the Otter Creek Labs Infinity is inefficient for bystander protection on the short-barrel MK18.  The muzzle (bystander) Suppression Rating drop to 25.4 illustrates the hazard increase directly and quantitatively.  Under no circumstances should the user anticipate that the vented 7.62 end cap will provide comparable protection to the solid or vented 5.56 end caps to personnel adjacent to the weapon system.  The hazard increase is severe.

Despite the uncontrolled combustion propagation from the vented 7.62 end cap on this host weapon, the extreme severity of standard untuned AR-15 ejection port blast results in this configuration still benefiting operator protection by significantly reducing blast pressure.  It is not necessarily the case that the 7.62 vented end cap Infinity is a quiet system. It is just that the AR-15, to the weapon operator, is exceedingly hazardous.  Ejection port blast loads are a primary driver of weapon operator hazard.  The efficacy of operator protection increase through this drastic back pressure reduction (albeit with severe muzzle blast loads) with the vented 7.62 end cap is presented in the full report.

A comprehensive comparison summary is provided below.

6.179.5 Suppression Rating Comparison (5.56x45mm from the MK18)

Figure 14 presents a comparison of the PEW Science Suppression Rating of the Otter Creek Labs Infinity, in three different end cap configurations, with that of several other silencers on the MK18 weapon system. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.

Figure 14. Suppression Rating Comparisons of the Otter Creek Labs Infinity and other rifle silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis

Figure 14 presents an overall summary of the postulated hazards to the operator and bystanders when fielding a variety of different silencers on the standard MK18 weapon system.  The three configurations of the Otter Creek Labs Infinity from this test program are shown in red.  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 Infinity with solid 5.56 end cap produces free field bystander hazard reduction on par with that of the highest performing designs; the PTR VENT 3 (6.135) and the HUXWRK FLOW 556 Ti (6.167).  This is a significant achievement, given the length of the Infinity, its distal momentum control with the solid 5.56 end cap, and its high early time flow rate.  The Infinity in this configuration surpasses the performance of the previous generation Otter Creek Labs Polonium (6.75) in both pure signature suppression, as well as in operator risk reduction.  The Infinity, even with its solid end cap, has lower back pressure than the Polonium due to its higher early-time flow rate.  This is, again, a significant achievement, given its extremely high muzzle (bystander) Suppression Rating. It is important to note that both the Polonium-K (6.95) and Polonium-30 (6.143) are significantly outperformed by this configuration of the Infinity.

  2. The free field operator (shooter) hazard reduction of the Otter Creek Labs Infinity with solid 5.56 end cap is significantly surpassed in operator protection by some other hybrid designs and flow-through designs, such as the aforementioned HUXWRX FLOW 556 Ti and PTR VENT 3, the CAT ODB (6.120), the CAT WB (6.129), and the PTR VENT Spiritus 556i (6.175).  Nonetheless, the holistic performance evolution of the Infinity over the legacy Polonium series is notable. 

  3. When utilizing the vented 5.56 end cap, the Otter Creek Labs Infinity provides significantly balanced performance on the standard untuned 5.56 MK18 weapon system.  In this configuration, the Infinity matches the operator protection of the vented Liberty Precision Machine Torch (6.126), while exceeding its bystander protection by over half a category.  In this configuration, the Infinity also almost approaches the operator protection of the HUXWRX HX-QD 556 (6.54), while also exceeding its bystander protection and distal momentum control, reducing blast load reflection severity.  However, the performance of the vented 5.56 end cap configuration of the Otter Creek Labs Infinity is surpassed holistically by other aforementioned hybrid designs, including the CAT WB, CAT ODB, and PTR PIP-equipped family.

  4. The Otter Creek Labs Infinity can also utilize the vented 7.62 end cap on a 5.56 automatic rifle. In this chosen configuration, the Infinity will exhibit more erratic combustion propagation, and although the performance can still be described as balanced, it is biased toward flow rate and ejection port blast hazard reduction, with less muzzle blast suppression. This is an important performance factor, because the excessive muzzle blast propagation from the ancillary primary axial bore vent area (larger primary end cap orifice) results in undue operator hazard increase from adverse blast wave coalescence. This is despite the high degree of ejection port blast hazard reduction, as detailed previously in this report.  In this configuration, the Infinity can be described as a less efficient HX-QD 556, or a more efficient Surefire SOCOM556-RC3 (6.151), in some respects.

  5. As discussed above, the Otter Creek Labs Infinity has highly variable performance on a short barrel AR-15 weapon system, based on end cap selection. It is recommended that the user select the configuration appropriate for their needs, based on desired level of protection for the operator and bystanders, compatible with dynamics of their particular weapon system.  It is likely that once the user chooses an appropriate configuration for their use case, the performance achieved will be significantly higher than legacy designs such as the Q Trash Panda (6.61), Thunder Beast Dominus (6.105), Energetic Armament ARX (6.82), Dead Air Sandman-S (6.92), and the Rugged Razor 762 (6.58).

PEW Science Research Note 12: The muzzle Suppression Rating of the Otter Creek Labs Infinity with solid 5.56 end cap is in the top 3 of the PEW Science laboratory MK18 Rankings, and the shooter’s ear Suppression Rating of the Infinity with the vented 5.56 end cap, characterizing operator risk in the free field, is entering the current top 10 in the Rankings.  Overall, the adaptability and versatility of the Infinity configurations represents a step forward in the Otter Creek Labs design pedigree, and places their new generation hybrid design among many top performing models.  PEW Science highly encourages the reader to examine the previous 7.62x51mm NATO bolt-action Infinity analytical report (6.178), in which the bolt-action performance of the silencer is examined in a higher-volume combustion regime.

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.

6.179.6 Review Summary: Otter Creek Labs Infinity 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 with the solid 5.56 end cap, the the Otter Creek Labs Infinity achieved a Suppression Rating™ of 40.2 in PEW Science testing.  With the vented 5.56 end cap, the Otter Creek Labs Infinity achieved a Suppression Rating of 33.5.  With the vented 7.62 end cap, the Otter Creek Labs Infinity achieved a Suppression Rating of 28.9.

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 Infinity is a severe-use mid-size 30 caliber rifle silencer with an advanced but flexible hybrid design.  In the role of a 5.56 rifle silencer, it is considered full-size.  The silencer is user-configurable for different blast load flow states and allows the operator to adapt the system to a variety of host weapons.  With a high early-time flow rate, the silencer may perform well on semiautomatic platforms even in its most restrictive configuration.  For sensitive platforms, the user may fully vent blast loads from multiple stages of the silencer, lowering back pressure to a minimum for this design.  The Infinity is 3D-printed from Inconel alloy and is expected to offer significant durability for hard use.

The Otter Creek Labs Infinity is a 30 caliber rifle silencer that is classified as a hybrid design in the PEW Science research taxonomy.  More specifically, the Infinity is classified as a staged hybrid.  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. Such attributes include the ability to reduce early-time shock reflections while significantly altering the rate of proximal and distal venting. These silencers may allow for minimal reciprocating weapon functional influence, while at the same time significantly suppressing signature to the operator and bystanders. Hybrid designs span a large range of the market in both brand and performance in different combustion regimes.

The Otter Creek Labs Infinity with solid 5.56 end cap produces free field bystander hazard reduction on par with that of the highest performing designs; the PTR VENT 3 and the HUXWRK FLOW 556 Ti.  This is a significant achievement, given the length of the Infinity, its distal momentum control with the solid 5.56 end cap, and its high early time flow rate.  The Infinity in this configuration surpasses the performance of the previous generation Otter Creek Labs Polonium in both pure signature suppression, as well as in operator risk reduction.  The Infinity, even with its solid end cap, has lower back pressure than the Polonium due to its higher early-time flow rate.  This is, again, a significant achievement, given its extremely high muzzle (bystander) Suppression Rating. It is important to note that both the Polonium-K and Polonium-30 are significantly outperformed by this configuration of the Infinity.

The free field operator (shooter) hazard reduction of the Otter Creek Labs Infinity with solid 5.56 end cap is significantly surpassed in operator protection by some other hybrid designs and flow-through designs, such as the aforementioned HUXWRX FLOW 556 Ti and PTR VENT 3, the CAT ODB, the CAT WB, and the PTR VENT Spiritus 556i.  Nonetheless, the holistic performance evolution of the Infinity over the legacy Polonium series is notable. 

When utilizing the vented 5.56 end cap, the Otter Creek Labs Infinity provides significantly balanced performance on the standard untuned 5.56 MK18 weapon system.  In this configuration, the Infinity matches the operator protection of the vented Liberty Precision Machine Torch, while exceeding its bystander protection by over half a category.  In this configuration, the Infinity also almost approaches the operator protection of the HUXWRX HX-QD 556, while also exceeding its bystander protection and distal momentum control, reducing blast load reflection severity.  However, the performance of the vented 5.56 end cap configuration of the Otter Creek Labs Infinity is surpassed holistically by other aforementioned hybrid designs, including the CAT WB, CAT ODB, and PTR PIP-equipped family.

The Otter Creek Labs Infinity can also utilize the vented 7.62 end cap on a 5.56 automatic rifle. In this chosen configuration, the Infinity will exhibit more erratic combustion propagation, and although the performance can still be described as balanced, it is biased toward flow rate and ejection port blast hazard reduction, with less muzzle blast suppression. This is an important performance factor, because the excessive muzzle blast propagation from the ancillary primary axial bore vent area (larger primary end cap orifice) results in undue operator hazard increase from adverse blast wave coalescence. This is despite the high degree of ejection port blast hazard reduction, as detailed previously in this report. In this configuration, the Infinity can be described as a less efficient HX-QD 556, or a more efficient Surefire SOCOM556-RC3, in some respects.

As discussed above, the Otter Creek Labs Infinity has highly variable performance on a short barrel AR-15 weapon system, based on end cap selection. It is recommended that the user select the configuration appropriate for their needs, based on desired level of protection for the operator and bystanders, compatible with dynamics of their particular weapon system.  It is likely that once the user chooses an appropriate configuration for their use case, the performance achieved will be significantly higher than legacy designs such as the Q Trash Panda, Thunder Beast Dominus, Energetic Armament ARX, Dead Air Sandman-S, and the Rugged Razor 762.

The muzzle Suppression Rating of the Otter Creek Labs Infinity with solid 5.56 end cap is in the top 3 of the PEW Science laboratory MK18 Rankings, and the shooter’s ear Suppression Rating of the Infinity with the vented 5.56 end cap, characterizing operator risk in the free field, is entering the current top 10 in the Rankings.  Overall, the adaptability and versatility of the Infinity configurations represents a step forward in the Otter Creek Labs design pedigree, and places their new generation hybrid design among many top performing models.  PEW Science highly encourages the reader to examine the previous 7.62x51mm NATO bolt-action Infinity analytical report, in which the bolt-action performance of the silencer is examined in a higher-volume combustion regime.

The Otter Creek Labs Infinity retail package ships without a mount.  While this lowers cost and gives the user maximum flexibility, it also requires the user to remain diligent and be responsible for their mounting system choice. Appropriate mount for both practical field use case and blast load dynamics is paramount; the Infinity has a significant degree of early-time venting.  This beneficial performance trait may be compromised through the use of mounts that induce undue blast load reflection, such as compensators like the "Cherry Bomb” and others.  Use of such devices may increase the effective back pressure of a system by elevating the Alpha parameter; the early-time blast load impulse accumulation inside the first expansion chamber of the silencer.  PEW Science encourages the user to contact the silencer manufacturer for a recommended mounting system for their requisite application(s).

The silencer is primarily constructed from Inconel 725 alloy; users may subject the silencer to abusive firing schedules without significant damage. PEW Science has not performed durability testing or evaluation of the Infinity.  The user is encouraged to contact the manufacturer for use guidance.

In this review, the Otter Creek Labs Infinity 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.