SSS.6.77 - Research Supplement: The Rugged Razor556 vs. Razor762 with 7.62mm and 5.56mm Endcaps on the MK18 (Members Only)
/The Rugged Razor556 vs. Razor762 with 7.62mm and 5.56mm Endcaps on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The Rugged Razor556 centerfire rifle silencer is compared to the Rugged Razor762 in this members-only Research Supplement. Parameters investigated are relative First Round Pop (FRP) and overall sound signature suppression performance characteristics on the MK18. Performance of the Razor762 with the standard 30 caliber endcap, as well as the standard Rugged 5.56mm endcap is highlighted, as was done in previous Member Research Supplement 6.59.
Note that the Rugged Razor556 endcap is unique to the Razor556 and not available for purchase separately. It is part of the holistic Razor556 design.
In the analysis, Rugged Razor design change 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:
Rugged Razor556 vs. Razor762 (6.77; this article)
Sound suppression performance of 30 caliber centerfire rifle silencers, on 5.56x45mm host weapons with reciprocating (automatic and semiautomatic) actions, is of interest 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 Razor762 with its standard 30 caliber endcap on the MK18. Previous Member Research Supplement 6.59 evaluated the Razor762 fitted with the standard Rugged 5.56mm endcap on the MK18. Concurrent with this publication, the Razor556 is evaluated on the MK18 (6.76). Public Suppression Rating data is summarized in 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.
It is also important to note that the holistic design of a silencer influences its performance on a weapon system; bore size is only one parameter. The Razor556, like the Razor762, is over-bored for the 5.56x45mm cartridge. However, as discussed in Review 6.76, the Razor556 possesses other design features not present in the Razor762, to include:
Different baffle quantity (one less baffle).
Different baffle spacing.
Different endcap orifice geometry.
The above design differences change the performance of Rugged Razor556 rifle silencer on the MK18 weapon system. The impacts of these design changes have been quantified by PEW Science.
Section 6.77.1 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.
Section 6.77.2 provides detailed comparisons of ear response to muzzle waveforms measured in the free field.
Section 6.77.3 provides detailed comparisons of ear response to waveforms measured near the shooter’s ear.
Section 6.77.4 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 the Rugged Razor556 on the MK18 compared with those of the Razor762 with its standard 30 caliber endcap and 5.56mm endcap. This supplement is part of ongoing PEW Science small arm weapon system sound signature research.
6.77.1 Overall Sound Suppression Performance Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Rugged Razor762 equipped with the 5.56mm 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 Razor556 is postulated to be approximately 6% louder than the 5.56mm endcap-equipped Razor762, to bystanders, during the first shot. The Razor556 is postulated to be approximately 11% quieter to bystanders, on average, than the 5.56mm endcap-equipped Razor762. It is likely that the Razor556 will not sound as “harsh.”
Shooter Perception:
To the personnel firing the MK18 weapon system, the use of the 5.56 mm endcap on the Razor762 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 Razor556 has a signature, to the shooter, that is on-par with the 30 caliber endcap-equipped Razor762, during the first shot. The Razor556 is slightly quieter to the shooter, on average, than the Razor762, regardless of Razor762 endcap choice.
PEW Science postulates that the 5.56mm endcap may provide more benefit to the shooter with the Razor762 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. It is further postulated that the performance of the Razor556 on a tuned MK18 host weapon system would benefit similarly. This postulation is based upon the similar flow rates of the two systems.
As stated in Review 6.76, the Rugged Razor556 is over-bored for the 5.56x45mm cartridge, just as the 30 caliber Razor762 is over-bored. In the PEW Science testing and analysis of the Razor762, it was determined that the excessively large bore diameter, coupled with the relatively low number of baffles (four) results in a relatively high mass flowrate (low back pressure; low PEW Science Omega Metric). It was further determined that by using a 5.56mm bore endcap, the flow rate is reduced, which increases sound suppression performance, particularly during the first shot.
The Razor556 possesses a similar bore size as the Razor762, and also possesses one less baffle, a different baffle spacing, and different endcap orifice geometry. Preliminary Omega_556 analysis by PEW Science indicates that the flow rate of the Razor556 is on-par with that of the Razor762 with a 5.56mm endcap. Bolt closing times from muzzle sound signature waveform measurements also strongly support this conclusion, as do the significant late time rarefaction in the waveforms measured at the shooter’s ear. This average flow rate similarity, between a silencer with one less baffle and a larger endcap orifice (the Razor556 possesses one less baffle than the Razor762 and the endcap orifice of the Razor556 is larger than the 5.56mm endcap of the Razor762, if equipped) may be counterintuitive. Several factors should be considered:
The Razor556 endcap orifice possesses an internal recess and outer chamfer, which shapes gas flow prior to exit and after exit.
The removal of the 3rd baffle (creating a larger space between the Razor556 new baffle 2 and new baffle 3) creates additional gas expansion volume which acts as limited stagnation relief for certain flow regimes, in certain time regimes.
PEW Science postulates that the above two changes both decrease the average gas flow rate through the Razor556, compared with the 30 caliber endcap-equipped Razor762, and bring the average flow rate on par with that of the 5.56mm endcap-equipped Razor762. However, PEW Science further postulates that while the average gas flow rate may be similar, the rate of fire significantly influences the flow rate. While measurable, these flow rate differences may not be of concern to many users. However, the fact that the Razor556 is measured to behave like a more restrictive silencer during a typical 5-round shot string, while having one less baffle, merits further study.
It is important to note that the over-bore of the Razor556 still results in some inefficiency during FRP, similar to the Razor762. 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 at the muzzle and ear being different (as with any silencers).
Fig 3. Normalized FRP Performance Summary (Supersonic 5.56x45mm MK18)
As discussed in Research Supplement 6.59, despite the significant increase in performance during the first shot of the Razor762 with the 5.56mm endcap, the use of the 5.56mm endcap does not provide as significant a benefit, on average, to personnel firing the weapon. However, it does result in a very similar improvement in suppression, to the shooter, over the Razor556. This is postulated to be due to sound field changes due to flow rate difference during the first shot. The enhanced endcap geometry of the Razor556 is postulated to mitigate adverse factors during FRP, to bystanders, which is reflected in the lower relative FRP at the muzzle. The Razor762 with 5.56mm endcap is slightly quieter to bystanders than the Razor556 during FRP.
It is important to note that personnel firing the weapon are still subject to ejection port signature, coupled with muzzle blast. The result of this coupling with the 5.56mm endcap-equipped Razor762 is still severe enough, on average, to not result in any signature improvements to the shooter over the use of the 30 caliber endcap (Figure 4) . Note that this is not necessarily a direct consequence of increased flow restriction (back pressure) from the smaller 5.56mm endcap orifice which typically manifests as increased ejection port signature severity on the automatic MK18 weapon system during firing.
The Razor556, however, is able to take advantage of significant muzzle suppression efficiency from its design improvements. Not only does this result in significantly more muzzle suppression than the Razor762, it results in more muzzle suppression than the 5.56mm endcap-equipped Razor762, on average. This allows for a measurable increase in Suppression Rating at the shooter’s ear with the Razor556, despite its slightly higher backpressure than the Razor762. It is highly likely that more than one shot will be necessary to note the suppression benefit of the Razor556 over a 5.56mm endcap-equipped Razor762, on the MK18.
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 silencers to both bystanders and to 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 below.
6.77.2 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.
6.77.2.1 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 Razor762 with the 5.56 mm endcap is postulated to sound significantly quieter than the same silencer with the 30 caliber endcap. The Razor556 is postulated to be approximately 6% louder than the 5.56mm endcap-equipped Razor762, to bystanders, during the first shot.
Note that in the very low frequency response regime, the 5.56 mm endcap-equipped Razor762 produces a slightly more severe ear response than does the 30 caliber endcap. This behavior significantly reverses above a hearing sensitivity of 1,000 Hz. The Razor556 induces an even higher low frequency inner ear response. It is not until 2,000 Hz that its signature induces similar response to the 5.56 mm endcap-equipped Razor762. These signatures most likely will manifest to bystander perception as the Razor556 sounding “boomy” during the first shot on the MK18, when compared to the Razor762.
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)
6.77.2.2 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-equipped Razor762 is quieter than with the 30 caliber endcap, on average.
The Razor556 is postulated to be approximately 11% quieter to bystanders, on average, than the 5.56mm endcap-equipped Razor762. It is likely that the Razor556 will not sound as harsh; this is due to the primary inner ear response divergence of the two silencers occurring at 3,000 Hz and above.
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)
6.77.3 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.
6.77.3.1 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 Razor762 with the 5.56 mm endcap is postulated to sound quieter than the same silencer with the 30 caliber endcap, during the first shot.
The Razor556 has a signature, to the shooter, that is on-par with the 30 caliber endcap-equipped Razor762, 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)
6.77.3.2 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 Razor762 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 Razor762 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.
The Razor556 is slightly quieter to the shooter, on average, than the Razor762, regardless of Razor762 endcap choice. The Razor556 also induces a slightly exaggerated inner ear response between 1,000 and 2,000 Hz.
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)
6.77.4 Research Supplement Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Rugged Razor762 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 Razor556 is postulated to be approximately 6% louder than the 5.56mm endcap-equipped Razor762, to bystanders, during the first shot. The Razor556 is postulated to be approximately 11% quieter to bystanders, on average, than the 5.56mm endcap-equipped Razor762. It is likely that the Razor556 will not sound as “harsh.”
Shooter Perception:
To the personnel firing the MK18 weapon system, the use of the 5.56 mm endcap on the Razor762 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 Razor556 has a signature, to the shooter, that is on-par with the 30 caliber endcap-equipped Razor762, during the first shot. The Razor556 is slightly quieter to the shooter, on average, than the Razor762, regardless of Razor762 endcap choice.
PEW Science postulates that the 5.56 endcap may provide more benefit to the shooter with the Razor762 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. It is further postulated that the performance of the Razor556 on a tuned MK18 host weapon system would benefit similarly. This postulation is based upon the similar flow rates of the two systems.
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 5.56mm endcap changes performance. Weapon system adjustment may be required for optimal use of the 5.56mm endcap. The Razor556 endcap is proprietary to the Razor556. It is possible that the use of different endcaps with the Razor556 will result in differing sound suppression performance. Testing of the Razor556 with different endcaps is the subject of possible 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.
