SSS.6.59 - Research Supplement: The Rugged Razor with the 5.56 Endcap (Members Only)
/The Rugged Razor with the 5.56 mm Endcap on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The Rugged Razor 30 caliber centerfire rifle silencer is evaluated with the 5.56 mm endcap in this members-only Research Supplement to examine its relative First Round Pop (FRP) and overall sound signature suppression performance characteristics on the MK18. Performance of the Razor is compared to that with the standard 30 caliber endcap. Impacts to the PEW Science Suppression Rating (Figure 1) on the standard PEW Science MK18 test host weapon system are investigated. Suppression Rating Rankings for other silencers can be found in Section 7 of the Standard.
Fig 1. PEW Science Suppression Rating Scale
Test data and analysis for the below rifle silencers on the MK18 host weapon have been published by PEW Science, to date:
Sound suppression performance of 30 caliber centerfire rifle silencers, on 5.56x45mm host weapons with reciprocating (automatic and semiautomatic) actions, is of concern to many weapon system operators. In addition to their multiple-cartridge size utility, 7.62mm bore silencers often possess higher flow rate (lower back pressure) than 5.56mm bore silencers of similar size and design envelope. This so-called over-bore may result in sound suppression performance degradation on 5.56x45mm platforms with some designs. Such performance degradation was highlighted in the previous testing and analysis of the Rugged Razor with its standard 30 caliber endcap on the MK18 (Figure 2).
Fig 2. Suppression Rating Comparisons Of The Rugged Razor With The OSS HX-QD 556, Saker 556, And SOCOM556-RC2 , Using PEW-SOFT 5.56x45mm Supersonic Test Data
Typically, silencers possessing a low Omega Metric exhibit low flow restriction (back pressure) which may result in improved sound signature suppression performance at the shooter’s ear on automatic weapon systems such as the MK18. However, when over-bore is significant enough, and flow rate reduction is achieved only through this simple mechanism, the severity of the muzzle signature from the weapon system may significantly impact the signature measured at the shooter’s ear.
In keeping with the intended high utility of using 30 caliber rifle silencers on multiple cartridges, some manufacturers offer interchangeable endcaps that may influence the performance and reduce net over-bore. Rugged Suppressors offers such a product with their 5.56 Front Cap. Use of the Rugged 5.56 Front Cap changes the performance of Rugged rifle silencers on weapon systems. The impact of these performance changes has been quantified by PEW Science.
Section 6.59.1 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.
Section 6.59.2 provides detailed comparisons of the measured muzzle and ear waveforms with the two endcaps.
Section 6.59.3 provides detailed comparisons of ear response to muzzle waveforms measured in the free field.
Section 6.59.4 provides detailed comparisons of ear response to waveforms measured near the shooter’s ear.
Section 6.59.5 presents some concluding thoughts.
This research supplement is intended to provide more information to PEW Science members with regard to the specific sound signature characteristics of 5.56 endcap use with the Rugged Razor on the MK18 compared with those from use of the standard 30 caliber endcap. This supplement is part of ongoing PEW Science small arm weapon system sound signature research.
6.59.1 Overall Sound Suppression Performance Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Rugged Razor equipped with the 5.56 mm endcap will always sound quieter than the same silencer with the 30 caliber endcap when using the MK18. The difference is most noticeable to bystanders during the first shot, as the 5.56 endcap reduces the FRP signature perceived by bystanders, significantly. The Suppression Rating at the Muzzle of the Rugged Razor on the MK18 increases from 16.5 to 20.5 with the 5.56 mm endcap.
Shooter Perception:
To the personnel firing the MK18 weapon system, the use of the 5.56 mm endcap will result in a noticeably less severe signature during the first shot than with the use of the standard 30 caliber endcap. As the weapon is continuously fired, the difference to the shooter, on average, is significantly less pronounced. On average, the shooter will not experience a reduced hearing risk by using the 5.56 endcap with the Rugged Razor on the MK18. The Suppression Rating at the Shooter’s Ear of the Rugged Razor on the MK18 slightly decreases from 18.6 to 18.5 with the 5.56 mm endcap.
PEW Science postulates that the 5.56 endcap may provide more benefit to the shooter on a tuned MK18 host weapon system than on the standardized MK18 system tested, but the benefit may not be significant. Further testing is needed.
As stated in Review 6.58, the Rugged Razor is a 30 caliber rifle silencer, and as such, is significantly over-bored for the 5.56x45mm weapon platform. The excessively large bore diameter, coupled with the relatively low number of baffles (four) result in a relatively high mass flowrate (low back pressure; low PEW Science Omega Metric). By using a 5.56 mm bore endcap, the flow rate is reduced, which increases sound suppression performance, particularly during the first shot. Normalized FRP performance is compared in Figure 3.
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 Razor at the muzzle and ear being different (as with any silencer).
Fig 3. Normalized FRP Performance Summary (Supersonic 5.56x45mm MK18)
Despite the significant increase in performance during the first shot, the use of the 5.56 mm endcap does not provide as significant a benefit, on average, to personnel firing the weapon. While still reducing overall signature to bystanders, personnel firing the weapon are still subject to ejection port signature, coupled with muzzle blast. The result of this coupling with the 5.56 endcap is still severe enough, on average, to not result in any signature improvements to the shooter (Figure 4). Note that this is not necessarily a direct consequence of increased flow restriction (back pressure) from the smaller 5.56 mm endcap orifice which typically manifests as increased ejection port signature severity on the automatic MK18 weapon system during firing.
PEW Science Member Research Note: The increased backpressure of the 5.56 mm endcap with the Rugged Razor is measurable. The difference in the Omega Metric parameter (Omega_556; not yet published) for the two endcaps on the Rugged Razor is present, but not largely significant. PEW Science postulates that differences in Omega Metric across some regions of the Omega Metric Scale may be more severe to certain weapon system operation than to others. This highlights the importance of Omega Zones, and the logarithmic nature of the parameter. PEW Science further postulates that the 5.56 endcap may provide more benefit to the shooter on a tuned MK18 host weapon system than on the standardized MK18 system tested, but the benefit may not be significant. Further testing is needed.
Fig 4. Normalized Average Performance Summary (Supersonic 5.56x45mm MK18)
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 6.59.3).
6.59.2 Comparisons of measured Muzzle and Ear Waveforms with the two Endcaps
For completeness, and to highlight specific differences in the gas dynamics measured when using the 5.56 mm endcap with the Rugged Razor, pressure and impulse waveforms measured 1.0 m left of the endcap are shown in Figure 5 for the first shot. Comparisons with the 30 caliber endcap and 5.56 mm endcap are shown.
Fig 5a. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signatures - Endcap Comparison, 28-AUG-2021
Fig 5b. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signatures - Endcap Comparison, 28-AUG-2021
Note that during the first shot, the coupled muzzle blast jet and bullet exit shockwave is significantly suppressed with the 5.56 endcap when compared to that measured with the 30 caliber endcap (Figure 5a). The rate of rise to maximum peak positive phase impulse, which inversely correlates to flow restriction (back pressure) is also lower with the 5.56 endcap; the smaller hole traps more gas, slowing the flow rate. The initial slope of the red waveform in Figure 5b is not as steep, as a result. Note that the impulse magnitude is still higher during FRP; this is due to ancillary combustion during FRP and the jet delay from the smaller orifice. The length of the positive pressure phase is prolonged from the endcap; the relayed rarefaction from the smaller jet forces the impulse accumulation higher with the 5.56 endcap. The signature with the 5.56 mm endcap is significantly less severe during FRP due to the lower peak pressure amplitude and impulse rise time delay, despite the higher impulse magnitude. This highlights the importance of holistic waveform parameters impacting hearing response.
Figure 6 displays the same comparison, but with Shot 3 from the two endcaps.
Fig 6a. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signatures - Endcap Comparison, 28-AUG-2021
Fig 6b. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signatures - Endcap Comparison, 28-AUG-2021
The same phenomena is observed in Figure 6 as was in Figure 5; the smaller orifice throttles the flow rate of the silencer. This time, the peak impulse amplitude with the 5.56 mm endcap is lower; ancillary combustion from FRP is no longer present and the flow rate comparison is more normalized.
Figure 7 displays both FRP and Shot 3 comparisons in impulse space, at the shooter’s ear.
Fig 7a. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signatures - Endcap Comparison, 28-AUG-2021
Fig 7b. Rugged Razor 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signatures - Endcap Comparison, 28-AUG-2021
During FRP (Figure 7a), the initial peak impulse is reduced to the shooter with the 5.56 mm endcap, with a higher later-time peak occurring. However, the expedient impulse decay followed by a slower prolonged positive phase impulse with the 30 caliber endcap at approximately 31.5 ms demonstrates a significantly different signature with the two systems, to the shooter. This difference becomes less pronounced later in the shot string (Figure 7b) in which the impulse delay of the 5.56 mm endcap is not as significant. It is at this point that the benefits of the smaller orifice are not realized to the shooter, due to increase in flow restriction in the operating system.
The following subsections of this Research Supplement present in-depth comparisons of human inner-ear modeling response to the FRP and average sound signatures.
6.59.3 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.
6.59.3.1 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 silencers. To personnel located 1.0 m left of the weapon muzzle, the Rugged Razor with the 5.56 mm endcap is postulated to sound significantly quieter than the same silencer with the 30 caliber endcap.
Note that in the very low frequency response regime, the 5.56 mm endcap produces a slightly more severe ear response. This behavior significantly reverses above a hearing sensitivity of 1,000 Hz.
Fig 8a. Comparison of FRP Human Inner Ear Response - 5.56x45mm at the Muzzle (Linear Scale)
Fig 8b. Comparison of FRP Low Frequency Human Inner Ear Response - 5.56x45mm at the Muzzle (Log Scale)
Fig 8c. Comparison of FRP High Frequency Human Inner Ear Response - 5.56x45mm at the Muzzle (Log Scale)
Fig 9a. Comparison of Average Human Inner Ear Response - 5.56x45mm at the Muzzle (Linear Scale)
6.59.3.2 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 silencers. To personnel located 1.0 m left of the weapon muzzle, the 5.56 mm endcap is quieter on the Rugged Razor than the 30 caliber endcap, on average.
Fig 9b. Comparison of Average Low Frequency Human Inner Ear Response - 5.56x45mm at the Muzzle (Log Scale)
Fig 9c. Comparison of Average High Frequency Human Inner Ear Response - 5.56x45mm at the Muzzle (Log Scale)
6.59.4 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.
6.59.4.1 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 Rugged Razor with the 5.56 mm endcap is postulated to sound quieter than the same silencer with the 30 caliber endcap, during the first shot.
Fig 10a. Comparison of FRP Human Inner Ear Response - 5.56x45mm at the Ear (Linear Scale)
Fig 10b. Comparison of FRP Low Frequency Human Inner Ear Response - 5.56x45mm at the Ear (Log Scale)
Fig 10c. Comparison of FRP High Frequency Human Inner Ear Response - 5.56x45mm at the Ear (Log Scale)
6.59.4.2 Average Ear Comparisons
Fig 11a. Comparison of Average Human Inner Ear Response - 5.56x45mm 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 Rugged Razor with the 5.56 mm endcap is postulated to sound slightly louder, on average than the same silencer with the 30 caliber endcap.
The use of the 5.56 mm endcap with the Rugged Razor on the MK18, in addition to resulting in a slightly more severe signature to the shooter, on average, also shifts the shooter’s hearing response slightly lower in frequency. PEW Science postulates this may be a result of the significantly less severe muzzle signature, and its characteristics impacting the shooter.
Fig 11b. Comparison of Average Low Frequency Human Inner Ear Response - 5.56x45mm at the Ear (Log Scale)
Fig 11c. Comparison of Average High Frequency Human Inner Ear Response - 5.56x45mm at the Ear (Log Scale)
6.59.5 Research Supplement Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Rugged Razor equipped with the 5.56 mm endcap will always sound quieter than the same silencer with the 30 caliber endcap when using the MK18. The difference is most noticeable to bystanders during the first shot, as the 5.56 endcap reduces the FRP signature perceived by bystanders, significantly.
Shooter Perception:
To the personnel firing the MK18 weapon system, the use of the 5.56 mm endcap will result in a noticeably less severe signature during the first shot than with the use of the standard 30 caliber endcap. As the weapon is continuously fired, the difference to the shooter, on average, is significantly less pronounced. On average, the shooter will not experience a reduced hearing risk by using the 5.56 endcap with the Rugged Razor on the MK18.
PEW Science postulates that the 5.56 endcap may provide more benefit to the shooter on a tuned MK18 host weapon system than on the standardized MK18 system tested, but the benefit may not be significant. Further testing is needed.
PEW Science recommends that users of Rugged rifle silencers on 5.56x45mm weapon systems remain cognizant of the effects of changing endcap orifice size. When endcap orifice size decreases, flow rate also decreases, raising back pressure. If the weapon system is gas sensitive, this may result in undesirable function or signature characteristics. Individual weapon system parameters may influence the degree to which the 5.56 mm endcap changes performance. Weapon system adjustment may be required for optimal use of the 5.56 mm endcap.
This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.
