SSS.6.109 - Research Supplement: The Quietest 300 BLK Subsonic Ammunition: Discreet Ballistics vs. S&B with the Rugged Razor762 (Members Only)
/The Rugged Razor with Discreet Ballistics and S&B Subsonic 300 BLK Ammunition
The Rugged Razor762 30 caliber centerfire rifle silencer is evaluated with two types of subsonic 300 BLK ammunition in this members-only Research Supplement to examine its relative First Round Pop (FRP) and overall sound signature suppression performance characteristics. Performance of the Razor762 with Discreet Ballistics 300 BLK 190gr Target ammunition is compared to that with S&B 300 BLK 200gr ammunition. Impacts to the PEW Science Suppression Rating (Figure 1) on the standard 8-inch barrel 300 BLK bolt action platform are investigated. Suppression Rating Rankings for other silencers can be found in Section 7 of the Standard.
Fig 1. PEW Science Suppression Rating Scale
Typically, subsonic 300 BLK suppressed weapon systems are employed to maximize low signature lethality in a given size envelope. Test data and analysis for the below rifle silencers on the standard 8-inch barrel bolt action platform have been published by PEW Science, to date:
All 19 of the above silencer configurations were tested with Discreet Ballistics 300 BLK 190gr Target ammunition to provide standardized performance metrics for analysis. The Discreet Ballistics cartridge is a specialized load chosen by PEW Science for testing due to its relatively consistent combustion characteristics, when compared to some other commercial ammunition on the market. The overall sound suppression performance summary of the above 19 configurations, with this cartridge, is shown below in Figure 2.
Fig 2. Suppression Rating Comparisons Of .30 Rifle Silencers Using PEW-SOFT 300 BLK Subsonic Test Data
While the Discreet Ballistics 300 BLK cartridge loading provides consistent combustion characteristics for testing purposes, it is not as widely available as some other commercial subsonic 300 BLK offerings on the current market. PEW Science acknowledges that a user may choose to use other subsonic 300 BLK ammunition, with potentially unknown performance attributes. In an effort to illustrate potential suppressed weapon system performance differential when using differing brands of ammunition, this article examines a very popular commercial loading; the S&B 200gr 300 BLK commercial cartridge. Its performance is compared with that of the Discreet Ballistics cartridge. Both measured unsuppressed and suppressed signature waveforms are compared, along with in-depth suppressed signature characteristics for the shooter and bystanders. The Rugged Razor762 is used in this comparison as internal PEW Science R&D data was collected with the silencer, with both ammunition types.
Section 6.109.1 provides an overall sound suppression comparison performance summary of the two ammunition types with the Rugged Razor762 at the muzzle and shooter’s ear.
Section 6.109.2 provides detailed comparisons of the measured muzzle and ear waveforms with the two ammunition types, both unsuppressed and suppressed with the Rugged Razor762.
Section 6.109.3 provides detailed comparisons of ear response to muzzle waveforms measured in the free field with the two ammunition types.
Section 6.109.4 provides detailed comparisons of ear response to waveforms measured near the shooter’s ear with the two ammunition types.
Section 6.109.5 again presents the concluding summary.
This research supplement is intended to provide more information to PEW Science members with regard to the specific sound signature characteristics of multiples types of subsonic 300 BLK ammunition. This supplement is part of ongoing PEW Science small arm weapon system sound signature research.
6.109.1 Overall Sound Suppression Performance Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, Discreet Ballistics ammunition will always sound quieter than S&B ammunition through the Rugged Razor762, when used with this weapon system. The difference is most noticeable to bystanders during the first shot, as there is a 41% difference in FRP severity 1.0 left of the end cap. The Suppression Rating at the Muzzle of the Rugged Razor762 on this platform decreases from 33.0 to 30.7 with the use of S&B ammunition.
Shooter Perception:
To the personnel firing the weapon system, the use of Discreet Ballistics ammunition will also always result in a noticeably less severe signature than will the use of S&B ammunition through the Razor762 on this platform. And, as the weapon is continuously fired, the difference to the shooter, on average, will become greater. The Suppression Rating at the Ear of the Rugged Razor762 on this platform decreases from 37.9 to 33.3 with the use of S&B ammunition.
Mechanisms:
The phenomena by which the S&B ammunition underperforms in signature reduction on this platform include unoptimized propellant loading for the barrel length of the weapon, facilitating erratic secondary combustion.
On average, when subsequent shots are performed in the absence of air to facilitate ancillary combustion, the performance differential between the two ammunition types changes. The severity of the S&B loading is reduced, relative to the Discreet Ballistics loading, compared to the severity during FRP. Less ancillary combustion occurs in the silencer, resulting in a 25% decrease in bystander signature differential. However, the consistent combustion of the Discreet Ballistics ammunition continues to pay dividends in close proximity to the shooter, and there is a 6% further increase in shooter’s ear differential. In summary, the Discreet Ballistics ammunition is quieter than the S&B ammunition during the first shot, and gets even quieter than the S&B, as the shot string continues. But, to bystanders, the difference during the shot string is not as pronounced.
Razor762 Performance:
It is possible that the difference in ammunition performance would be reduced with a longer silencer, and/or a silencer with significantly higher FRP suppression performance. This phenomenon is the subject of future PEW Science Member Research.
This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.
As stated in Review 6.108, the standard PEW Science test ammunition for the subsonic 300 BLK publications presented, to date, has been Discreet Ballistic 190gr Target Ammunition. The consistency of this ammunition is relatively high for factory loadings. Deviations noted in the signature histories, from shot to shot, most often result from silencer gas dynamics and not ammunition variation. Furthermore, regardless of ammunition consistency, 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.
However, when changing ammunition types, the differences in combustion consistency across manufacturers / brands can be significant. A comparison of the Discreet Ballistics 190gr target loading and S&B 200gr loading, through the Rugged Razor762, during FRP, is shown in Figure 3. Note that the performance is normalized.
As noted, the relative the Muzzle and Ear FRP measurements shown in Figure 3 are not comparable to one another. Muzzle numbers should be compared with muzzle, and ear with ear. This is a consequence of the chosen normalization and the hearing damage potential with the S&B ammunition at the muzzle and ear being different (as it would be with any silencer and ammunition).
Fig 3. Normalized FRP Performance Summary (Subsonic 300 BLK)
During the first shot (first round pop, or “FRP”), the intensity of the signature, to both bystanders and the shooter, is more severe when using the S&B subsonic loading compared to that of the Discreet Ballistics subsonic loading. Both loadings are subsonic. It is the combustion characteristics that significantly differ. This is examined in the following section.
On average, when subsequent shots are performed in the absence of air to facilitate ancillary combustion, the performance differential between the two ammunition types changes (Figure 4). The severity of the S&B loading is reduced, relative to the Discreet Ballistics loading, compared to the severity during FRP. Less ancillary combustion occurs in the silencer, resulting in a 25% decrease in bystander signature differential (0.84 vs. 0.59, previously). However, the consistent combustion of the Discreet Ballistics ammunition continues to pay dividends in close proximity to the shooter, and there is a 6% further increase in shooter’s ear differential (0.64 vs. 0.70, previously). In summary, the Discreet Ballistics ammunition is quieter than the S&B ammunition during the first shot, and gets even quieter than the S&B, as the shot string continues. But, to bystanders, the difference during the shot string is not as pronounced.
PEW Science Member Research Note: The overall FRP severity differential being more severe at the muzzle, than on average, is driven by the mechanism of erratic secondary combustion of propellant. It is likely that the propellant charge in the S&B loading is less optimally formulated for the 8-in barrel of the test host, resulting in excess propellant burning in late time. During FRP, when air is present in the system, this excess burning is even more pronounced. For an illustration of this secondary combustion, unsuppressed with no silencer, the following section presents the free field signatures in the impulse regime.
Fig 4. Normalized Average Performance Summary (Subsonic 300 BLK)
The data shown in Figure 3 and Figure 4 is intended to present the likely human relative perception of FRP and average signature severity magnitudes of the silencer to both bystanders and the shooter. It is important to note that the human inner ear responds differently to certain frequencies. On average, it is postulated that the relations in the above figures will directly correlate to human inner ear response. However, some users may have hearing sensitivity that is compromised or different than others in certain frequency ranges. Those phenomena are considered in this article (Section 6.109.3).
6.109.2 Comparisons of measured Muzzle and Ear Waveforms with the two Ammunition Types
For completeness, and to highlight specific differences in the gas dynamics measured when using the two ammunition types, impulse waveforms measured 1.0 m left of the bare muzzle are shown in Figure 5 for an unsuppressed five shot string of fire.
Fig 5a. Unsuppressed Discreet Ballistics 190gr 300BLK Target Loading Muzzle Sound Impulse Signatures
Fig 5b. Unsuppressed S&B 200gr 300BLK Target Loading Muzzle Sound Impulse Signatures
Note that when unsuppressed, the initial peak impulse amplitude of the two ammunition types is comparable. Note that the above figures use the same scale on both the horizontal axis [time, ms] and vertical axis [impulse, Pa-ms]. However, in the S&B impulse signatures (Fig. 5b), the excess propellant described in the preceding section is shown to burn, creating excessive impulse accumulation in later time. In addition to this excess impulse occurring, it occurs inconsistently from shot to shot. The nonuniform combustion profile, along with inconsistency, produces anomalies in the signature, regardless of the unsuppressed or suppressed state of the weapon system.
To illustrate how the above anomalies in the unsuppressed state translate to the suppressed state, the same exercise is repeated for the impulse waveforms measured at the muzzle with the two ammunition types, this time through the same weapon system with the Rugged Razor762. Discreet Ballistics waveforms are presented in Figure 6a, with S&B waveforms presented in Figure 6b.
Fig 6a. Rugged Razor762 Suppressed Discreet Ballistics 190gr 300BLK Target Loading Muzzle Sound Impulse Signatures
Fig 6b. Rugged Razor762 Suppressed S&B 200gr 300BLK Target Loading Muzzle Sound Impulse Signatures
Similar phenomena is observed in Figure 6 as was in Figure 5; the inconsistent combustion results in erratic impulse accumulation. As discussed in the preceding section, it is worse during FRP due to the extra oxygen facilitating ancillary combustion with the propellant in the S&B loading; the mechanism is worsened.
Figure 7 displays additional comparisons in the impulse regime, at the shooter’s ear. The phenomena are also evident at that location.
Fig 7a. Rugged Razor762 Suppressed Discreet Ballistics 190gr 300BLK Target Loading Ear Sound Impulse Signatures
Fig 6b. Rugged Razor762 Suppressed S&B 200gr 300BLK Target Loading Ear Sound Impulse Signatures
It is clear that both during FRP, and on average, the signature from the two ammunition types, unsuppressed or suppressed, is different. In Figure 4 and Figure 5, the overall FRP and Average inner ear damage risk severity differentials were presented. Further comparison is possible, and may be prudent, depending on the user. To that end, the following subsections of this Research Supplement present in-depth comparisons of human inner-ear modeling response to the FRP and average sound signatures with the two ammunition types through the same Rugged Razor762 silencer.
6.109.3 Comparisons of Ear Response to Muzzle Waveforms Measured in the Free Field
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. The human inner ear responds to different sound pressure frequencies with varying sensitivity. Physically, these frequencies excite different regions of the basilar membrane within the cochlea. The human ear is typically most sensitive to sounds that excite the membrane near a frequency of 4,000 Hz. However, the ear may be exercised, and therefore damaged, at different physical regions. It is postulated that this inner ear response directly correlates to the perceived loudness of suppressed small arms.
PEW Science Research Note: As stated in previous Research Supplements, it is important not misconstrue the frequency-domain data in this Research Supplement with a simple frequency analysis (Fourier transform) of the time-domain overpressure waveforms presented in the reviews. The data shown in this research supplement is the output from analytical human inner ear modeling with the measured test data used as free-field overpressure loading input.
6.109.3.1 FRP Muzzle Comparisons
Figure 8 presents the results of an inner ear analysis performed using measured sound overpressure waveforms from the first shots in the referenced tests. The curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 8a shows the response on the vertical axis with a linear scale. Fig 8b and Fig 8c show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the two silencer configurations. To personnel located 1.0 m left of the weapon muzzle, the Discreet Ballistics ammunition is postulated to sound significantly quieter than the S&B ammunition through the same silencer.
The behavior occurs across much of the range of human inner ear response during the first shot, to bystanders. Note the higher than typical differential at approximately 7,000 Hz; this higher frequency inner ear response is postulated to be due to the “sharp” report of excess propellant burning in the S&B ammunition during FRP.
Fig 8a. Comparison of FRP Human Inner Ear Response - 300 BLK at the Muzzle (Linear Scale)
Fig 8b. Comparison of FRP Low Frequency Human Inner Ear Response - 300 BLK at the Muzzle (Log Scale)
Fig 8c. Comparison of FRP High Frequency Human Inner Ear Response - 300 BLK at the Muzzle (Log Scale)
Fig 9a. Comparison of Average Human Inner Ear Response - 300 BLK at the Muzzle (Linear Scale)
6.109.3.2 Average Muzzle Comparisons
Figure 9 presents the average results of an inner ear analysis performed using measured sound overpressure waveforms from all shots in the referenced tests. Again, the curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 9a shows the response on the vertical axis with a linear scale. Fig 9b and Fig 9c again show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the two configurations. To personnel located 1.0 m left of the weapon muzzle, the Discreet Ballistics ammunition is quieter than the S&B ammunition, just as it is during the first shot. However, as was previously shown in Figure 3, the differential is not as severe. This is due to the consumption of oxygen within the system not allowing the excess propellant in the S&B ammunition to continue burning as readily.
Fig 9b. Comparison of Average Low Frequency Human Inner Ear Response - 300 BLK at the Muzzle (Log Scale)
Fig 9c. Comparison of Average High Frequency Human Inner Ear Response - 300 BLK at the Muzzle (Log Scale)
6.109.4 Comparisons of Ear Response to Waveforms Measured near the Shooter’s Ear
The sound signatures measured at the ear during the tests of each endcap are significantly different than those measured at the weapon muzzle and this difference is not only shown in the average peak sound pressure and impulse measurements, but also with inner ear analysis.
6.109.4.1 FRP Ear Comparisons
Figure 10 presents an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from the first shots in both tests. Fig 10a shows the response on a linear vertical scale. Fig 10b and Fig 10c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively. To personnel firing the weapon, the Discreet Ballistics ammunition is postulated to sound quieter than the S&B ammunition with the same silencer, during the first shot.
The differential between the two cartridges is more uniform throughout the range of inner ear response to the shooter than it is to bystanders. Nonetheless, the peak severity differential is 30%, as was also presented in Figure 3.
Fig 10a. Comparison of FRP Human Inner Ear Response - 300 BLK at the Ear (Linear Scale)
Fig 10b. Comparison of FRP Low Frequency Human Inner Ear Response - 300 BLK at the Ear (Log Scale)
Fig 10c. Comparison of FRP High Frequency Human Inner Ear Response - 300 BLK at the Ear (Log Scale)
6.109.4.2 Average Ear Comparisons
Fig 11a. Comparison of Average Human Inner Ear Response - 300 BLK at the Ear (Linear Scale)
Figure 11 presents the average results from an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from all the shots in the referenced tests. Fig 11a shows the response on a linear vertical scale. Fig 11b and Fig 11c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively. To personnel firing the weapon, the Discreet Ballistics Ammunition is postulated to sound louder, on average than S&B ammunition with the same silencer.
And, on average, the differential in signature to the shooter, between the two ammunition types, increases. The maximum differential increases from 30% to 36%.
Fig 11b. Comparison of Average Low Frequency Human Inner Ear Response - 300 BLK at the Ear (Log Scale)
Fig 11c. Comparison of Average High Frequency Human Inner Ear Response - 300 BLK at the Ear (Log Scale)
6.109.5 Research Supplement Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, Discreet Ballistics ammunition will always sound quieter than S&B ammunition through the Rugged Razor762, when used with this weapon system. The difference is most noticeable to bystanders during the first shot, as there is a 41% difference in FRP severity 1.0 left of the end cap. The Suppression Rating at the Muzzle of the Rugged Razor762 on this platform decreases from 33.0 to 30.7 with the use of S&B ammunition.
Shooter Perception:
To the personnel firing the weapon system, the use of Discreet Ballistics ammunition will also always result in a noticeably less severe signature than will the use of S&B ammunition through the Razor762 on this platform. And, as the weapon is continuously fired, the difference to the shooter, on average, will become greater.
Mechanisms:
The phenomena by which the S&B ammunition underperforms in signature reduction on this platform include unoptimized propellant loading for the barrel length of the weapon, facilitating erratic secondary combustion.
On average, when subsequent shots are performed in the absence of air to facilitate ancillary combustion, the performance differential between the two ammunition types changes. The severity of the S&B loading is reduced, relative to the Discreet Ballistics loading, compared to the severity during FRP. Less ancillary combustion occurs in the silencer, resulting in a 25% decrease in bystander signature differential. However, the consistent combustion of the Discreet Ballistics ammunition continues to pay dividends in close proximity to the shooter, and there is a 6% further increase in shooter’s ear differential. In summary, the Discreet Ballistics ammunition is quieter than the S&B ammunition during the first shot, and gets even quieter than the S&B, as the shot string continues. But, to bystanders, the difference during the shot string is not as pronounced.
Razor762 Performance:
It is possible that the difference in ammunition performance would be reduced with a longer silencer, and/or a silencer with significantly higher FRP suppression performance. This phenomenon is the subject of future PEW Science Member Research.
This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.
