SSS.6.146 - Mercy Firearms Pluto and the CZ 452 .22 Bolt-Action
/Mercy Firearms Pluto on a CZ 452 .22 Bolt Action with 16-in Barrel
The Pluto is distributed by Mercy Firearms. It is a compact and lightweight 22 caliber rimfire silencer, intended to suppress .22LR. It has a 1-inch diameter and is 5 inches long. The silencer is entirely constructed of DMLS (3D-printed) titanium. The silencer may be installed on host weapons threaded 1/2”-28-tpi. In this test, an adapter was used to convert the native host weapon threads from 1/2”-20tpi. The silencer weighs 2.1 ounces, as tested. The Pluto can be obtained from Mercy Firearms.
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 for public research 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 white paper was funded in part by PEW Science Project PEW-Mercy-073-001-23. Therefore, data pertaining to the Pluto in this Sound Signature Review is published with the express written permission of Mercy Firearms.
This Sound Signature Review contains single-test results using the Mercy Firearms Pluto mounted to the CZ 452 American bolt-action rifle, chambered in .22LR with a 16-inch barrel. CCI Standard Velocity 40gr ammunition was used in the test.
Section 6.146.1 contains the Mercy Firearms Pluto test results and analysis.
Section 6.146.2 contains Suppression Rating comparisons with selected .22 rimfire silencers in the subsonic ammunition combustion regime.
Section 6.146.3 contains the review summary and PEW Science laboratory staff technical opinions.
Summary: When paired with the CZ 452 American bolt-action rifle and fired with CCI SV .22 LR ammunition, the Mercy Firearms Pluto achieved a composite Suppression Rating™ of 93.2 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
6.146.1 Mercy Firearms Pluto Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the Mercy Firearms Pluto is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. This is a members-only review and includes pressure and impulse waveforms measured at the shooter’s ear. PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
Table 1. Mercy Firearms Pluto Sound Metric Summary
6.146.1.1 SOUND SIGNATURES AT THE MUZZLE
Real sound pressure histories from a 5-shot test acquired with PEW-SOFT™ are shown below. The waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science laboratory sound signature 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 laboratory testing; the recognized 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 are shown in Figure 1a. A zoomed-in timescale displays the region of peak sound pressure in Figure 1b, for the first three shots. The real sound impulse (momentum transfer potential) histories from the same 5-shot test are shown in Figure 2. Again, full and short timescales are shown.
Fig 1a. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Muzzle Sound Pressure Signature
Fig 1b. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Muzzle Sound Pressure Signature, Short Time Window
Figure 2a. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Muzzle Sound Impulse Signature
Figure 2b. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Muzzle Sound Impulse Signature
The Mercy Firearms Pluto is compact; smaller than typical rimfire silencers. Although a full length .22LR rimfire bolt-action rifle is a relatively low pressure host weapon platform, the Pluto does still exhibit high performance, regardless of size. When considering its size and weight, the performance is even more significant when compared to that of some other silencers presented in the public research pedigree, to date.
There are several relatively unique features of the Pluto signature measured on this platform, including:
No measurable or perceptible first-round-pop (FRP) in pressure space (Figure 1) or impulse space (Figure 2).
Extreme signature consistency (Fig. 1b primary jetting and Fig. 2b resulting momentum accumulation).
Unusually greater negative phase pressure amplitude (Fig. 1b).
PEW Science Research Note 1: As discussed, the performance characteristics of the Pluto are significant, regardless of size. In particular, the extremely short duration gas momentum pulses from primary jetting, evidenced by the pronounced negative phase in (3), above, are unusual. This gas throttling behavior, occurring in such a small length envelope, is significant. The Pluto is not a low back pressure system. PEW Science postulates that the Pluto’s high performance is best showcased on non-reciprocating systems.
PEW Science Research Note 2: Like the previously evaluated CAT SR (6.140), the Mercy Firearms Pluto is 3D printed titanium and extremely light weight. The Pluto is smaller than the SR and weighs approximately 0.7 ounces less than the SR. As discussed in 6.140.1 and showcased in 6.141.1, low silencer mass also influences sound signature, directly, by changing the natural frequency of the primary vibrational mode of the total weapon system such that impulsive noise events from mechanical impact are subject to a lower degree of system damping, and thus higher amplitude resonance. In the subsonic rimfire ammunition combustion regime, with silencers exhibiting the degree of signature suppression of the Pluto and SR, these types of variations may generally be audible to the user, subject to host selection and operating system.
As noted above, the Pluto does not produce FRP on this platform. Bystanders are postulated to experience almost identical signature severity throughout the shot string, with the tested ammunition.
The rimfire silencer performance Rankings are now expanding; the Mercy Firearms Pluto joins the CAT SR, the Resilient Suppressors Jessie’s Girl (6.125) and the Rugged Oculus in both its configurations (6.1) in the current published dataset. In addition to bolt-action rifle evaluation, some of these silencers have also been evaluated on the subcompact semiautomatic Beretta 21A rimfire pistol. Additional evaluations in the rimfire ammunition combustion regime by PEW Science are forthcoming. Consult the PEW Science Rankings Section for the complete public testing and analysis library.
PEW Science Research Note 3: Users should note that performance of rimfire silencers on long and short barrels may be significantly different, even with subsonic ammunition, depending on silencer design.
6.146.1.2 SOUND SIGNATURES AT SHOOTER’S EAR
Real sound pressure histories from the same 5-shot test acquired with PEW-SOFT at the shooter’s ear are shown below. Again, 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 primary sound signature pressure histories at the ear for all 5 shots are shown in Figure 3. The primary sound signature history is shown on the left. A zoomed-in timescale is displayed on the right, in the region of peak sound pressure. The real sound impulse (momentum transfer potential) histories at the ear from the same 5-shot test are shown in Figure 4. Full and short timescales are shown.
Figure 3a. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Ear Sound Pressure Signature
Figure 3b. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Ear Sound Pressure Signature, Short Time Window
Figure 4a. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Ear Sound Impulse Signature
Figure 4b. Mercy Firearms Pluto Subsonic .22 LR Bolt Action Ear Sound Impulse Signature
The compact Pluto exhibits a high level of signature suppression on this platform. Although the signature does have significant components from muzzle blast, much of the signature does originate from internal combustion and the firing mechanism of the system.
PEW Science Research Note 4: The mechanical operation of the trigger and firing assembly, as well as the ignition and deflagration of priming compound in the rimfire case and primary propellant, contribute to an overall externally measured signature, including resonance at high sound-speed through the steel barrel, into the titanium silencer, and produce an overall signature that is non-trivial to the shooter with the Mercy Firearms Pluto, in addition to external muzzle blast.
The Pluto exhibits muzzle blast suppression to the shooter, on this platform, that is significant, especially for its size. The components of the signature from internal combustion and resonance do influence the severity of the signature at the shooter’s ear. These measurable phenomena are more noticeable than with heavier silencers, for example. The higher early time impulse accumulation in Figure 4b partially illustrates this phenomenon. This accumulation of wave momentum contains components from system firing mechanism and resonance elements that are coupled in the human shooter perception time regime. This total early time signature is unique to all host firearm and silencer combinations; it is an inherent system property.
Whereas FRP from the Pluto is postulated to be imperceptible to bystanders, there is a slightly nominal perceptibility of FRP to the shooter on this system. The FRP to the shooter is, for all intents and purposes, still nullified.
PEW Science Research Note 5 (General Rimfire Bolt-Action Rifle System Suppression): If a user desires a Suppression Rating (at the muzzle or shooter’s ear) that is higher than exhibited by the highest performance silencers shown in the Silencer Sound Standard on rimfire bolt-action rifle, it may be prudent for the user to explore different host options, such as rimfire systems with higher mass or impedance mismatches that may contain firing-pin impact noise to a greater degree. Internal material wave propagation may be changed by layering of various materials in a composite structure in a weapon stock, for example. Reduction in signature in such a manner is outside the scope of this article. However, primary mechanical noise limits are the subject of future PEW Science research. Although the PEW Science Suppression Rating Scale is designed for small arms signature damage risk criterion (DRC) applicability, the extreme ends of the scale may be used to quantify such limits, outside the bounds of DRC applicability. It is extremely important to note that mechanical firing system noise (action noise) may change only by changing the mass of an attached silencer, all other things equal, due to dynamic system resonance. This phenomenon is measurable and has been explored in the aforementioned studies.
PEW Science Research Note 6: The signature of a high performance rimfire silencer with subsonic ammunition fired from a bolt-action rifle, at the shooter’s head, is significantly suppressed and may not sound like a “gunshot” to the operator or to bystanders. It is important for operators and bystanders to remain cognizant of the potential hazards of firearm use and the potential lethality of such weapon systems; the operation of such systems, if not in accordance with weapon and silencer manufacturer instructions, may still result in serious injury or death.
6.146.2 Suppression Rating Comparison - Subsonic .22 LR
The Mercy Firearms Pluto was developed to maximize pure sound signature reduction (PEW Science Suppression Rating) in a relatively small and extremely lightweight envelope. Figure 5 shows a performance comparison of rimfire silencer configurations tested on a bolt-action rifle shown in public PEW Science testing, to date. Suppression Ratings are shown for both the shooter and bystanders.
Figure 5. Suppression Rating Comparisons Of Rimfire Silencers Using PEW-SOFT subsonic .22 LR Bolt-Action Test Data
The Mercy Firearms Pluto exhibits relatively high performance on this host weapon system, and it does so with consistent signature production and no perceptible FRP. In the current dataset, it meets or exceeds the muzzle suppression performance of the long configuration of the Rugged Oculus (6.1) and the Resilient Suppressors Jessie’s Girl (6.125) while being shorter than both of those silencers, and significantly lighter.
Although the Pluto does not exhibit the suppression performance of the CAT SR (6.140) on this platform, the Pluto’s design is not as advanced, and it is shorter than the SR. Nonetheless, the Pluto’s performance is notable and the consistency of the Pluto’s performance rivals that of the CAT SR and the long configuration of the Oculus; these three silencer configurations produce the most consistent suppression performance on this host weapon of those tested by PEW Science, to date. For the Pluto to achieve performance consistency such as this, at a high performance level, is particularly notable due to its 5-inch length and close to 2-ounce weight.
It should be noted that Suppression Ratings in the 90-zone indicate a significantly suppressed signature. At this level of firearm signature suppression, the Suppression Rating scale quantifies signatures that may not present as similar to gunshots, to most observers. Caution is recommended by both system operators and bystanders (see Research Note 7, below).
It is extremely important to note that mechanical firing system noise (action noise) may change only by changing the mass of an attached silencer, all other things equal, due to dynamic system resonance. This phenomenon is measurable and explored in article 6.141 with CAT SR on the Beretta 21A.
PEW Science Research Note 7: The signature of a high performance rimfire silencer with subsonic ammunition fired from a bolt-action rifle, at the shooter’s head, is significantly suppressed and may not sound like a “gunshot” to the operator or to bystanders. It is important for operators and bystanders to remain cognizant of the potential hazards of firearm use and the potential lethality of such weapon systems; the operation of such systems, if not in accordance with weapon and silencer manufacturer instructions, may still result in unintended serious injury or death. The user is encouraged to be mindful of the degree to which sound signature suppression, and resulting personnel hazards, can vary across designs. Small arm weapon system suppression performance is a spectrum. The PEW Science Suppression Rating and the Silencer Sound Standard help quantify this spectrum for end users and industry, objectively.
6.146.3 Review Summary: Mercy Firearms Pluto on a CZ 452 .22 Bolt Action with 16-in Barrel
When paired with the CZ 452 American bolt-action rifle and fired with CCI SV .22 LR ammunition, the Mercy Firearms Pluto achieved a composite Suppression Rating™ of 93.2 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 Mercy Firearms Pluto is a rimfire silencer that exhibits high performance with an extremely light weight and compact size envelope. Despite being 5 inches long and approximately 2 ounces, the Pluto provides rimfire suppression performance comparable to longer and heavier silencers. The silencer is sealed; its monolithic DMLS titanium body may be cleaned with a variety of chemical solutions.
The Mercy Firearms Pluto is compact; smaller than typical rimfire silencers. Although a full length .22LR rimfire bolt-action rifle is a relatively low pressure host weapon platform, the Pluto does still exhibit high performance, regardless of size. When considering its size and weight, the performance is even more significant when compared to that of some other silencers presented in the public research pedigree, to date.
The Pluto exhibits relatively high performance on this host weapon system, and it does so with consistent signature production and no perceptible FRP. In the current dataset, it meets or exceeds the muzzle suppression performance of the long configuration of the Rugged Oculus and the Resilient Suppressors Jessie’s Girl while being shorter than both of those silencers, and significantly lighter.
Although the Pluto does not exhibit the suppression performance of the CAT SR on this platform, the Pluto’s design is not as advanced, and it is shorter than the SR. Nonetheless, the Pluto performance is notable and the consistency of the Pluto’s performance rivals that of the CAT SR and the long configuration of the Oculus; these three silencer configurations produce the most consistent suppression performance on this host weapon of those tested by PEW Science, to date. For the Pluto to achieve performance consistency such as this, at a high performance level, is particularly notable due to its 5-inch length and close to 2-ounce weight.
Servicing the Pluto is accomplished by soaking with the user’s choice of cleaning solution to remove lead fouling. In general, the user is encouraged to contact the manufacturer for cleaning and servicing directives.
PEW Science has not evaluated the durability of the Mercy Firearms Pluto, nor its performance on cartridges other than subsonic .22 LR. It is important for the user to contact the manufacturer to determine the suitability of firing schedules and use cases.
In this review, the Mercy Firearm Pluto performance metrics depend upon suppressing a subsonic rimfire cartridge on a bolt-action rifle. While the sound signature of such systems can be suppressed to levels that may not sound like a “gunshot” to the operator or to bystanders, PEW Science encourages the reader to remain vigilant with regard to all subsonic rimfire cartridge suppression claims. It is important for operators and bystanders to remain cognizant of the potential hazards of firearm use and the potential lethality of such weapon systems; the operation of such systems, if not in accordance with weapon and silencer manufacturer instructions, may still result in serious injury or death.
The hazard potential of subsonic rimfire rifle use is not insignificant. PEW Science encourages the reader to consider the Suppression Rating when deciding on an appropriate silencer and host weapon combination for their desired use.
