SSS.6.18 - Intermediate Results Summary: Compact and Mid-Size .308 Rifle Silencers - Suppression and Back Pressure
/Compact and Mid-Size .30 Rifle Silencers on a .308WIN Bolt Action Rifle with 20-inch Barrel
The previous Sound Signature Reviews, up to and including Review 6.16, have featured various silencers on several host weapons. Eight of those reviews feature centerfire rifle silencers; two of which were tested in two configurations each due to modularity of the silencer body or end-cap. This is a comparative summary of the objective performance of those ten total configurations.
This Results Summary is part of ongoing PEW Science small arm weapon system sound signature research.
The data below references the Suppression Rating which is keyed to the shot dose scale at the top of this Results Summary. The data also contains relative back pressure metrics which have been reported throughout the centerfire rifle reviews, to date, in order to frame objective flow rate characteristics of the silencers for their prospective use on semi- and fully-automatic small arms. This data is the first of its kind in the public domain and represents a direct contribution of PEW Science member-funded research to the state of practice.
6.18.1 Sound Signature Review Results
It is not always possible to determine relative, objective loudness from only the measured average peak sound pressure amplitude and measured peak sound pressure momentum transfer potential (impulse). Therefore, the Suppression Rating also considers physical ear response to measured sound signatures. Specific detailed data of that response is contained in members-only research supplements which quantify not only loudness, but also metrics like tone. Nonetheless, the gross Suppression Rating metrics publicly presented herein allow the user to frame objective loudness comparisons for both the shooter and bystanders.
Figure 1 presents the data summary of compact and mid-size centerfire rifle suppressors shown in the public Sound Signature Reviews, to date. The results shown are calculated from real test data acquired with PEW-SOFT. Please note the following:
The time to reach peak gas momentum transfer potential, as measured 1.0 m left of the weapon muzzle, is the objective quantity used to generate the back pressure data summary.
The waveform characteristics of unsuppressed shots with the same ammunition used in the respective tests are used in the calculations. The unsuppressed relative back pressure and unsuppressed absolute Suppression Rating quantities are shown.
The first shot from each silencer test is omitted from the back pressure computations due to internal gas environment characteristics within the silencer (first round pop) that influence peak impulse amplitude, wave-shape, and timing. All unsuppressed shots are included.
Back Pressure Data is normalized to the silencer with the highest back pressure shown (the CGS Helios QD). The Suppression Rating at the muzzle (correlating to bystander perception) and at the ear (correlating to shooter perception) are absolute.
Data is presented from test results using supersonic ammunition; relative performance of the silencers in the subsonic flow regime may differ and is the subject of future PEW Science research interest.
PEW Science Research Note: As of February 2021, back pressure characterization has undergone refinement and Rev.2 of the Back Pressure Metric has been developed. Research is ongoing. Please see back pressure research updates starting with Sound Signature Review 6.36.
Fig 1. Supersonic Performance Summary for .30 Rifle Silencers as of 06-AUG-2020
Detailed Sound Signature Reviews containing the raw data used to generate the summary in Figure 1 are linked below:
This is not an exhaustive collection of .30 rifle silencers on the current market, but does represent a cross-section of design variation in the compact to mid-size category. It is important to note that all silencers listed, with the exception of the Q Trash Panda and the SilencerCo Omega 300, are intended for severe firing schedules on automatic host weapons, as stated by the designers and manufacturers. This durability rating is not an objective quantity presented in this summary but is a characteristic noted to frame the reader’s understanding of overall product capabilities. Detailed construction and performance characteristics, along with mounting details, are presented in the respective Sound Signature Review of each silencer. All silencers listed above, other than the VOX S, can be obtained from Silencer Shop.
6.18.2 Data Interpretation
The length of the silencers in the aforementioned reviews range from 5.4 inches (the Sandman-K) to 7.5 inches (the Radiant in its long configuration). Current silencer market nomenclature dictates that .30 centerfire rifle silencers longer than those in that range may be considered full size.
Back Pressure and Sound Suppression: Silencer back pressure is directly related to gas flow rate. Suppression Rating is strongly correlated to this flow rate, which is measured from the rise time to peak momentum transfer potential of gasses outside the silencer; however, there are notable data outliers:
Dead Air Sandman-S: This silencer is able to achieve a Suppression Rating at the ear above 30, while possessing 39% of the back pressure potential possessed by the CGS Helios QD. This represents an extremely efficient back pressure reduction balance with high(er) sound suppression.
Q Trash Panda: This silencer is the runner-up to the Sandman-S in balancing high(er) sound suppression with back pressure with a notable Suppression Rating at the ear of 33, with back pressure potential that is 47% of that possessed by the CGS Helios QD.
Energetic Armament VOX S: This silencer achieves a Suppression Rating very close to 30 at the shooter’s ear, but possesses a back pressure potential that is 66% of the Helios potential. This represents the least efficient back pressure reduction balance with sound suppression in the group, but it is important to note that the balance is close to that of the CGS Helios QD with solid end-cap (the quietest silencer).
Dead Air Sandman-K: This silencer achieves the lowest back pressure, yet still achieves a higher Suppression Rating at the shooter’s ear than both the CGS Helios QD with the vented end-cap (a purposefully low back pressure configuration) and the Rugged Radiant in its short configuration (a silencer configuration with only two baffles). To date, this represents the most extreme back pressure reduction balance with sound suppression observed in PEW Science testing, based upon the computed metrics.
Pure Sound Suppression: In many designs, sound suppression (and therefore the Suppression Rating) is directly related to the number of baffles in the silencer, its volume, its length, and primary axial orifice flow area. This trend is observed in the results; silencers with many baffles like the Omega 300 or Trash Panda exhibit high sound suppression, whereas silencers with fewer baffles exhibit lower sound suppression. There are internal features that influence the correlation, but this parametric relationship is observed in the performance of most of the products tested.
When moving outside the traditional interior design envelope of baffle geometry and allowing additional flow paths, efficiencies in sound suppression are gained. This is observed in the performance of the CGS Helios QD; it is not the longest silencer in the group, nor does it contain the most volume. However, it does possess internal geometry that directs flow through an outer annulus. This flow geometry, coupled with various interior design features, enable the Helios to achieve a Suppression Rating at the shooter’s ear that is class-leading.
PEW Science note: Quantifying the efficiency metric capturing the balance of back pressure and sound suppression is the subject of continued PEW Science research interest. PEW Science thanks you for your support.
