SSS.6.142 - Otter Creek Labs Polonium-30 and the Savage Model 10 PC .308 (Free Version)

/

Otter Creek Labs Polonium-30 on a Savage Model 10 .308 with 20-in Barrel

The Polonium-30 is designed and manufactured by Otter Creek Labs. It is a 30 caliber centerfire rifle silencer, intended to suppress many cartridges with projectiles appropriately sized to travel through the bore. It has a 1.625-inch diameter and is 5.8 inches in length, without a mount. The total length with the included direct thread adapter is 6.3 inches. The user may choose to install third-party adapters compatible with the 1.375”-24tpi system. The silencer is tubeless; the entirety of the welded assembly is constructed of H900 heat treated 17-4 stainless steel. As tested, the silencer weighs 13.9 ounces and the 5/8”-24tpi direct-thread mount weighs weighs 1.9 ounces, for a total system weight of 15.8 ounces. The Polonium-30 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 data production for this Sound Signature Review was funded in part by PEW Science Project PEW-OCL-077-001-23. Therefore, data pertaining to the Polonium-30 in this Sound Signature Review is published with the express written permission of Otter Creek Labs, LLC.

This review contains single test results using the Polonium-30 with its direct thread mount on the Savage Model 10 Precision Carbine rifle, chambered in .308WIN with a 20-inch barrel. Federal XM80 149gr ammunition was used in the tests.

  • Section 6.142.1 contains the Polonium-30 test results and analysis.
  • Section 6.142.2 contains back pressure and Suppression Rating comparisons with selected .30 rifle silencers possessing a PEW Science Back Pressure Metric, Ω [Pa-1] in Omega Zones 4 and below. An updated Ω metric chart for the full suite of publicly evaluated .30 rifle silencers is also provided in this section. Further information about the Ω metric and Omega Zones can be obtained in PEW Science Research Supplement 6.40 (Public Article).
  • Section 6.142.3 contains the review summary and PEW Science laboratory staff technical opinions.

Summary: When paired with the Savage M10 20” .308 and fired with Federal XM80, the Otter Creek Labs Polonium-30 with its direct thread mount achieved a Suppression Rating™ of 37.1 in PEW Science testing.

When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Polonium-30 achieved a composite Suppression Rating™ of 30.9 in PEW Science testing.

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

Relative Suppression Rating Performance is Summarized in SSS.7 - PEW Science Rankings

6.142.1 Otter Creek Labs Polonium-30 Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Polonium-30 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 Polonium-30 Sound Metric Summary

 

6.142.1.1 SOUND SIGNATURES AT THE MUZZLE

Real sound pressure histories acquired with PEW-SOFT™ are shown below. The waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science testing is 1.0 MS/s (1 MHz). The peaks, shape, and time phasing (when the peaks occur in relation to absolute time and to each other) of these raw waveforms are the most accurate of any firearm silencer testing publicly available. PEW-SOFT data is acquired by PEW Science independent testing; the industry leader in silencer sound research. For more information, please consult the Silencer Sound Standard.

The primary sound signature pressure histories for all 5 shots with the Polonium-30 are shown in Figure 1a. The sound signatures of Shot 1, Shot 2, and Shot 3 are shown in Figure 1b, in early time. The real sound impulse (momentum transfer potential) histories from the same 5-shot test are shown in Figure 2a. In Figure 2b, a shorter timescale is shown comparing the impulse of the first three shots.

Fig 1a. Otter Creek Labs Polonium-30 Bolt Action Rifle Muzzle Sound Pressure Signature

Fig 1b. Otter Creek Labs Polonium-30 Bolt Action Rifle Muzzle Sound Pressure Signature, Short Time Window

Figure 2a. Otter Creek Labs Polonium-30 Bolt Action Rifle Muzzle Sound Impulse Signature

Figure 2b. Otter Creek Labs Polonium-30 Bolt Action Rifle Muzzle Sound Impulse Signature, Short Time Window

Figure 1b shows a 1.2 millisecond long portion of the sound pressure signatures of the first three rounds fired from the Otter Creek Labs Polonium-30, as measured 1.0 m left of the muzzle. There are several significant waveform features labeled:

  1. Internal combustion is within the silencer is relatively consistent and reaches a peak of 122.0 dB.

  2. The end cap exit event, consisting of bullet shock and the initial jet, results in a peak overpressure magnitude of 141.7 dB.

  3. The first major jets occur relatively quickly, progressively increasing after the first shot.

  4. Rarefaction increases during the shot string, proportionally.

  5. Onset of secondary jetting begins consistently at approximately 30.4 ms.

This is a somewhat typical sequence observed when firing supersonic .308WIN ammunition from a bolt-action rifle with an attached silencer that exhibits relatively low to moderate flow restriction (back pressure). Internal silencer design can significantly influence the measured timing and pressure amplitudes. Preliminary back pressure comparisons are shown in Section 6.142.3 of this review, with the PEW Science Back Pressure Metric, Ω [Pa-1]. Note that weapon system influence is a function of both Ω and early-time wave propagation factors which may be measured inside the system, in close proximity to the muzzle orifice. These factors include the so-called PEW Science alpha parameter; a subject of future research.

PEW Science Research Note 1: The Otter Creek Labs Polonium-30 is, for all intents and purposes, structurally identical to the Polonium (6.75), other than the bore aperture.  Whereas the Polonium is a dedicated 6mm (243 caliber) bore silencer, the Polonium-30 is a 7.62mm (30 caliber) bore silencer.  The internal geometry is similar in both silencers, across all 6 baffles.

Despite the relative simplicity of the Polonium-30 design, it does produce some of the consistent gas momentum characteristics with 7.62x51mm combustion as that of the smaller-bored Polonium with 5.56x45mm combustion. Readers should note that the Polonium-30 has also been evaluated with 5.56x45mm ammunition, and that data is available in article 6.143 in which a direct comparison of performance between the Polonium-30 and Polonium is possible.

PEW Science Research Note 2: Although the Polonium-30 is the same length as the full-size Polonium 5.56 silencer, the Polonium-30 may be considered mid-size or compact for a 30 caliber silencer. As a consequence of its shorter length and fewer baffles than some competing designs, along with their simplicity, there are distinct performance characteristics of note that are apparent in the above measured signatures, including the immediate and significant first-round-pop (FRP) divergence (Fig. 1b and Fig. 2b), as well as the progressively increasing degree of rarefaction noted in (4), above (Fig. 1b). Rather than experiencing significant FRP on this platform, its signature increases in severity as the system is fired and its temperature increases. Therefore, bystanders will experience FRP relative to the second shot, but subsequent shots may be more severe. The combustion gas propagation through the simplified geometry of the Polonium, at the pressure and duration of the 7.62x51mm cartridge, normalizes to a more severe amplitude as the shot string progresses. This phenomenon is relatively uncommon on this host weapon platform, and is a consequence of the aforementioned geometry.

PEW Science Research Note 3: The Polonium-30 exhibits holistic performance on the weapon system that is relatively close to that of the Dead Air Nomad-30 (6.43).  The Polonium-30 performs very similarly to the now discontinued Otter Creek Labs PR30S (6.49); a silencer with different baffle geometry and gas dynamics that possesses similar gross signature severity.  Another silencer with similar overall performance to the Polonium-30 on this host weapon is the CGS Hyperion K (6.28), though the flow rate of the Hyperion K is higher due to its hybrid design.  Rifle design variations and their performance efficacy are explored in Research Supplement 6.124.

Overall performance of the Polonium-30 on a .308 bolt-action rifle is bounded on the low end by lower performing systems such as the Q Trash Panda (6.4) and Rugged Radiant (6.12). The performance is bounded on the high end by higher performing systems such as the Surefire SOCOM762-RC2 (6.26) and the Silencer Central Banish 30 (6.74).

Consistent with the above measured pressure and impulse waveform features, the computed PEW Science Omega Metric is relatively low to moderate, placing the silencer in Omega Zone 4. Relative Suppression Rating and flow restriction (back pressure) data is presented in Section 6.142.2 of this review.

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 has made a concerted effort to characterize the FRP phenomenon with true physiological human inner-ear response analyses. Additional PEW Science Member Research Supplements containing this information are released periodically.

6.142.2 Relative Suppression Rating and Back Pressure Comparisons (.30 Rifle Silencers)

The Otter Creek Labs Polonium-30 suppressor is intended to offer moderate sound signature suppression in a relatively compact size envelope.  Due to its size, baffle quantity, and blast chamber geometry, it may produce moderate back pressure. PEW Science has developed an empirical relation to quantify the back pressure (flow restriction) of silencers. Figure 5 and Figure 6 show supersonic suppression and back pressure comparisons between selected 7.62mm (30 caliber) rifle silencers shown in public PEW Science Sound Signature Reviews, as of the date of this review publication. The results shown in Figure 5 and Figure 6 are calculated from real test data acquired with PEW-SOFT. Please note the following:

  1. The PEW Science Back Pressure Metric, Ω [Pa-1], may be generated for any silencer and suppressed weapon system using any suitable raw external overpressure signature data acquired 1.0 m left of the silencer end cap. PEW Science highly recommends data acquisition in accordance with The Silencer Sound Standard.
  1. Omega Zones are presented in Table 3, below, which are intended to provide guidance to weapons developers, silencer designers, and end-users, with regard to flow restriction characteristics of different silencer designs. It is very important to note that silencers possessing a relatively high Ω can still provide functional use on weapon systems. Some weapon systems are more sensitive to Ω than others.
  1. It is important to note that a silencer’s Omega Zone can shift when using a mounting scheme that differs from that used in the testing referenced in the published PEW Science Sound Signature Reviews. This phenomenon occurs due to some silencer mounting schemes significantly influencing flow restriction with some silencer designs.
  1. The theoretical lower limit of flow restriction, or so-called "zero back pressure" would be represented by the unsupressed state, Ω = 0 [Pa-1].
  1. PEW Science acknowledges that other dynamic events occur within a suppressed weapon system that can also influence weapon function. Therefore, PEW Science acknowledges that Ω is not the sole parameter one must consider for total supppressed weapon system operation. However, PEW Science postulates that the Ω metric influence can be significant. Note that weapon system influence is also a function of early-time wave propagation factors which may be measured inside the system, in close proximity to the muzzle orifice. These factors include the so-called PEW Science Alpha parameter; a subject of future research.
  1. The Back Pressure Metric relations are most easily viewed on a logarithmic scale (See Figure 6).

Figure 5. Omega Back Pressure Metric And Suppression Rating Comparisons Of .308 Rifle Silencers Using PEW-SOFT Data and Analysis

As stated above, the PEW Science Back Pressure Metric is most easily viewed on a logarithmic scale. The metric is nonlinear; the shape of the trend in the data presented in Figure 6, below, illustrates the potential thresholds of extreme flow rate (approaching the unsuppressed state) and extreme flow restriction (approaching the trapping of the maximum amount of combustion byproducts in a system).

Figure 6. Omega Back Pressure Metric Comparisons Of .308 Rifle Silencers Using PEW-SOFT Data and Analysis

Omega characterizes silencer back pressure. It is important to note that back pressure is not blow back. The back pressure of a silencer is the flow restriction it introduces in a suppressed weapon system. The blow back phenomenon that can occur during the use of a suppressed weapon system is caused by the reciprocating system actuating too early relative to overpressure decay within the weapon system, resulting in exposure of excessive internal system overpressure to atmosphere. Some weapons may be tuned to function well with silencers in a high Omega Zone. Some weapons may require low-Omega silencers due to constraints in their operating system(s). Omega metric technical details can be found in PEW Science Public Research Supplement 6.40.

Table 3. PEW Science Back Pressure Metric Omega Zones And Suppressed Weapon System Functional Descriptions

As stated above, weapon system influence is a function of both Ω and early-time wave propagation factors which may be measured inside the system, in close proximity to the muzzle orifice. These factors include the so-called PEW Science Alpha parameter; a subject of future research.  The Otter Creek Labs Polonium-30 was tested with its included direct-thread mount which most likely does not significantly influence early time shock reflections near the muzzle.  Mount geometry, chamber geometry, and the blast baffle shape all contribute to a postulated early-time flow restriction, in addition to late-time flow restriction characterized by Omega. 

The Polonium-30 exhibits holistic performance on the weapon system that is relatively close to that of the Dead Air Nomad-30 (6.43).  The Polonium-30 performs very similarly to the now discontinued Otter Creek Labs PR30S (6.49); a silencer with different baffle geometry and gas dynamics that possesses similar gross signature severity.  Another silencer with similar overall performance to the Polonium-30 on this host weapon is the CGS Hyperion K (6.28), though the flow rate of the Hyperion K is higher due to its hybrid design.  Rifle design variations and their performance efficacy are explored in Research Supplement 6.124.

Overall performance of the Polonium-30 on a .308 bolt-action rifle is bounded on the low end by lower performing systems such as the Q Trash Panda (6.4) and Rugged Radiant (6.12). The performance is bounded on the high end by higher performing systems such as the Surefire SOCOM762-RC2 (6.26) and the Silencer Central Banish 30 (6.74).

PEW Science urges the reader not to misconstrue a low Omega metric with the mirroring of unsuppressed weapon function, nor a high Omega Metric with absolute use prohibition on semi-automatic systems. Each weapon system may experience varying sensitivity to different Omega Zones and users may exhibit varying preference for weapon system function and operability. The Zones are provided by PEW Science to assist the reader with determination of postulated applicability of silencer types, as some users may only have experience with certain silencers. The Omega Metric is one performance indicator; it allows overall flow rate phenomena to be categorized independently from sound signature suppression performance. Note that weapon system influence is also a function of early-time wave propagation factors which may be measured inside the system, in close proximity to the muzzle orifice.

It is extremely important to note that peak sound pressure [dB], peak sound impulse [dB-ms], and Omega (Ω) [Pa-1], alone, do not determine the sound supression performance of a silencer. It is the combination of these and other waveform parameters that form the total sound signature and the influence on human inner ear response. The PEW Science Suppression Rating computation considers all of these factors.

6.142.3 Review Summary: Otter Creek Labs Polonium-30 on a Savage Model 10 .308 with 20-in Barrel

When paired with the Savage M10 20” .308 and fired with Federal XM80, the Otter Creek Labs Polonium-30 with its direct thread mount achieved a Suppression Rating™ of 37.1 in PEW Science testing.

When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Polonium-30 achieved a composite Suppression Rating™ of 30.9 in PEW Science testing.

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 Polonium-30 is a compact to mid-size 7.62mm rifle silencer that possesses competitive sound signature suppression performance with many silencers on the market in its size class.  Users should note that its sister silencer, the Polonium, is a 6mm (243 caliber) silencer of identical size, intended for higher performance when fielding on 5.56x45mm systems.

The rear of the Polonium is threaded for universal mount adaptation. The user may choose to install third-party adapters compatible with the 1.375”-24tpi system. This feature allows for significant adaptability of the silencer, should the included direct-thread adapter not be used.

The Polonium-30 exhibits holistic performance on the weapon system that is relatively close to that of the Dead Air Nomad-30.  The Polonium-30 performs very similarly to the now discontinued Otter Creek Labs PR30S; a silencer with different baffle geometry and gas dynamics that possesses similar gross signature severity.  Another silencer with similar overall performance to the Polonium-30 on this host weapon is the CGS Hyperion K, though the flow rate of the Hyperion K is higher due to its hybrid design.  Rifle design variations and their performance efficacy are explored in Research Supplement 6.124.

Overall performance of the Polonium-30 on a .308 bolt-action rifle is bounded on the low end by lower performing systems such as the Q Trash Panda and Rugged Radiant. The performance is bounded on the high end by higher performing systems such as the Surefire SOCOM762-RC2 and the Silencer Central Banish 30.

Like its sister silencer, the Polonium, the Polonium-30 may fit the role of a “duty-use” silencer, in that it may be subjected to severe firing schedules. PEW Science postulates that the blast baffle geometry and construction of the Polonium-30, like the Polonium, is conducive to such use. However, PEW Science has not subjected the Polonium-30 to severe automatic firing schedules and encourages the user to contact the manufacturer for guidance prior to use in such applications.

In this review, the Polonium-30 performance metrics depend upon suppressing a supersonic centerfire rifle cartridge; no easy 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 .308WIN cartridge are significant; the measured pressure and impulse magnitudes, and their durations, illustrate this fact.

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.