SSS.6.97 - HUXWRX CA$H 9K and the Heckler and Koch SP5 9x19mm Subgun (Free Version)
/HUXWRX CASH 9K on the HK SP5 9x19mm Subgun with 8.9-in barrel
The CA$H 9K is designed and manufactured by HUXWRX (formerly OSS). It is a 9mm centerfire silencer, intended to suppress many cartridges with projectiles appropriately sized to travel through the bore, up to and including .350 Legend. The CASH 9K has a 1.345-inch primary diameter and is 4.9 inches long. The silencer may be attached to a pistol with an internal inertial-decoupling piston possessing 1/2-28tpi or 13.5x1mm LH threading. It also may be used with the included direct thread mount which increases the system length to 5.2 inches. Other mounting options are possible due to the rear of the silencer body being threaded with the SilencerCo Alpha thread pattern. The so-called Flow-Baffles of the CA$H 9K, as well as the internal adapter cage and direct thread mount, are constructed of 17-4 heat treated stainless steel. The end cap of the silencer is aluminum, and the tube body is titanium. The silencer is user-serviceable and weighs 7.5 ounces with the include direct thread mount, as tested. The CASH 9K can be obtained from Silencer Shop.
PEW Science is an independent private testing laboratory and also the world’s only publicly funded suppressed small arms research cooperative. Testing, data analysis, and reporting is generated with funding provided by PEW Science members. Any test data that is generated with any portion of private funding contains this disclosure. The testing and data production for this Sound Signature Review was funded in part by PEW Science Project PEW-HUX-035-001-22. Therefore, data pertaining to the CA$H 9K in this Sound Signature Review is published with the express written permission of OSS Suppressors, LLC.
This Sound Signature Review contains single-test results using the HUXWRX CASH 9K with the direct thread mount on the semiautomatic Hecker and Koch SP5 subgun, chambered in 9x19mm NATO with a 8.9-inch barrel. Speer Lawman 147gr ammunition was used in the test, in which its velocity was subsonic. The standard PEW Science HK SP5-A2 test host weapon system is described in Public Research Supplement 6.85.
Section 6.97.1 contains the CASH 9K test results and analysis.
Section 6.97.2 contains Suppression Rating comparisons of the CA$H 9K with the RS9 and GSL Phoenix fired on the Heckler and Koch SP5-A2.
Section 6.97.3 contains the review summary and PEW Science subjective opinions.
Summary: When paired with the 8.9-in barrel HK SP5-A2 with 80-deg locking piece and fired with Speer Lawman 147gr, the HUXWRX CA$H 9K mounted with the direct thread mount achieved a composite Suppression Rating™ of 47.8 in PEW Science testing. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
The Semiautomatic Pistol (Handgun) performance of the HUXWRX CA$H 9K on the HK P30L is detailed in Sound Signature Review 6.96, in which it achieved a Suppression Rating of 45.3.
Relative Suppression Rating Performance is Summarized in SSS.7 - PEW Science Rankings
6.97.1 HUXWRX CASH 9K Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the CASH 9K tested with the direct thread mount is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. The data acquired 0.15 m (6 in) right of the shooter’s ear is only available to membership supporters of PEW Science and the Silencer Sound Standard. You can support PEW Science testing, research, and development with a membership, here. State-of-the-art firearm sound signature testing and research conducted by PEW Science is supported by readers like you.
Table 1. HUXWRX CA$H 9K Sound Metric Summary
6.97.1.1 SOUND SIGNATURES AT THE MUZZLE
Real sound pressure histories from a 6-shot test acquired with PEW-SOFT™ are shown below. Six cartridges were loaded into the magazine, the fire control group positioned to single-shot, and the weapon was fired until the magazine was empty, and the bolt returned to battery with an empty chamber. The HK MP5 family of submachineguns do not possess a bolt-hold-open feature. Only five shots are considered in the analysis. The signatures of Shot 6 are displayed in the data presentation but are not included in the analysis to maintain consistency with the overall PEW Science dataset and bolt-closing signatures. 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 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 testing; the industry leader in silencer sound research. For more information, please consult the Silencer Sound Standard.
The primary sound signature pressure histories for all 6 shots with the HUXWRX CASH 9K are shown in Figure 1a. The sound signatures of Shot 1, Shot 2, and Shot 3 are shown in Figure 1b, in early time. The real sound impulse (momentum transfer potential) histories from the same 5-shot test are shown in Figure 2a. In Figure 2b, a shorter timescale is shown comparing the impulse of Shot 1, Shot 2, and Shot 3.
Fig 1a. HUXWRX CA$H 9K subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Pressure Signature
Fig 1b. HUXWRX CA$H 9K subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Sound Pressure Signature
Figure 2a. HUXWRX CA$H 9K subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature
Figure 2b. HUXWRX CA$H 9K subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature
PEW Science Technology Note: The following is a description of silencer technology derived from PEW Science research: The OSS / HUXWRX Flow-Through technology used in HUXWRX rifle silencers achieves efficacy by routing combustion gasses through overlapping annular paths, axially forward and aft, and finally exhausting these gasses through distal vents, to atmosphere. This gas management begins in early time, in conjunction with the primary flow through the bore. The suppression performance efficiency of HUXWRX rifle silencers is therefore directly proportional to combustion pressure and duration. As pressure and duration drop, the proportion of flow occupying the primary bore increases; this decreases suppression efficiency of the Flow-Through technology. This phenomenon is demonstrated in the testing and analysis of the HUXWRX OSS HX-QD 762 in the supersonic 7.62x51mm combustion regime (Review 6.41) and the respective review of the same silencer in the subsonic 300 BLK combustion regime (Review 6.45). The silencer is shown to lose efficiency when suppressing the subsonic 300 BLK cartridge.
The subsonic 9x19mm pistol cartridge shares some characteristics with that of the subsonic 300 BLK cartridge referenced above; namely lower combustion pressure and duration. In order for the Flow-Through technology to achieve efficacy within these combustion parameters, it must be fully accessed in the time regime of interest. Therefore, the HUXWRX CASH 9K does not utilize the same Flow-Through technology; instead, it uses the HUXWRX Flow-Baffle. The Flow-Baffle is a hybrid internal design in which combustion gasses are still routed immediately to an outer annulus for later distal venting. However, the principle differentiator between this technology and the rifle technology is the presence of traditional baffle geometry along the primary bore path. With a shorter annular path and a traditional baffle core, the Flow-Baffle is able to manage lower pressure combustion products immediately and over a shorter duration. PEW Science postulates that scaling traditional Flow-Through design for use with subsonic 9x19mm cartridge would be inefficient and that the hybrid Flow-Baffle design produces greater efficiency in this regime. Current PEW Science test data and analysis strongly supports this postulation.
PEW Science Analytical Discussion: The HUXWRX CASH 9K is an extremely compact and high flow rate pistol caliber silencer specifically intended for use on submachine guns (though it may also be used on pistols, as shown in previous Sound Signature Review 6.96). In the current published dataset, there are performance characteristics of note. Additional submachinegun performance context will be presented in future PEW Science Sound Signature Reviews. The reader should note the following:
The free field muzzle pressure signatures (Figure 1a) are presented, as typical, in accordance with the same data pedigree as the signatures presented for supersonic rifle silencers on the reciprocating standard PEW Science MK18 test host weapon system described in Public Research Supplement 6.51. The reciprocating standard PEW Science HK SP5-A2 test host weapon system is described in Public Research Supplement 6.85, and produces similar, albeit different, late-time phenomena (bolt closing signatures).
The muzzle pressure signature from the HK SP5-A2 is not as significantly suppressed with the CASH 9K (Figure 1) as it is with the Resilient Suppressors RS9 (Review 6.90) or GSL Phoenix (Review 6.86).
The rise-time to maximum positive phase impulse (Figure 3) from the CASH 9K is significantly faster than from the Phoenix and even faster than the RS9. This gas behavior is indicative of less flow restriction (lower backpressure).
The first-round-pop (FRP) from the CASH 9K is higher than from the larger RS9 and Phoenix on the full-size HK SP5, to bystanders, in accordance with PEW Science inner ear modeling. The FRP of the CASH 9K on this platform is significant to bystanders.
The performance of the CASH 9K at the shooter’s ear on this platform is significantly influenced by its high flow rate. It exhibits not only the highest published PEW Science Suppression Rating at the shooter’s ear on this platform to date, but does it in an extremely compact size.
PEW Science Research Note 1: The ancillary combustion during Shot 1 is observed in both pressure space (Figure 1a) and impulse space (Figure 2a). As typically indicated, 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. Ammunition consistency can play a role in the determination of FRP, however, the close examination of measured pressure and impulse waveforms typically excludes ammunition from the possible factors influencing true FRP, due to the relative consistency of most high quality factory ammunition.
PEW Science Research Note 2: The FRP from the CASH 9K on this platform exhibits early-time impulse accumulation delay (see Figure 2b). Specifically, this results from a delay of precursor jet propagation (Figure 1b, at approximately 29.8 ms). PEW Science postulates that the early-time gas dynamics within the silencer during the first shot are responsible for this delay, as the precursor flow from the SP5 barrel occupies the annular space. Upon ancillary combustion propagation (primary FRP jetting), the impulse accumulation tracks with the initial slopes of subsequent shots (Figure 2b, 30 ms) and then overtakes them, per typical (Figure 2b, 30.2 ms).
PEW Science Research Note 3: As in most semiautomatic weapon testing, a second pressure pulse originates from the ejection-port signature of the weapon and it occurs early enough in time such that its waves coalesce with that of the muzzle signature. However, in late time (at approximately 85 ms in Figure 1a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 still displays this event due to the bolt not remaining open after the sixth and final round is fired from the magazine on the HK SP5-A2 weapon system. Nonetheless, the bolt is closing on an empty chamber.
PEW Science Research Note 4: The closing time of the HK SP5-A2 bolt is directly related to the flow restriction of a silencer used with the weapon system. PEW Science has determined bolt closing time variation from the unsuppressed state to be a reliable indicator of silencer back pressure, with strong correlation with the PEW Science Back Pressure Metric, Omega with rifle cartridges, particularly on the MK18 weapon system. PEW Science Omega Metric research in the subsonic 9x19mm combustion regime with the HK SP5-A2 and SP5K-PDW weapon systems is underway. Note that the PEW Science HK SP5-A2 possesses an 80-deg locking piece in its bolt carrier group, which may result in lower bolt carrier group rearward velocity than systems possessing standard angle locking pieces. This lower rearward velocity may result in delayed forward return velocity, when compared with other systems.
It is also important to note that PEW Science has determined bolt closing time to be an unreliable indicator upon upper receiver fouling in some weapon systems, such as the MK18. Sound signatures are typically not influenced by this fouling, as these kinematics occur in late time, after gas venting to atmosphere. Note that the roller-delayed blowback action of the HK SP5-A2 is significantly different than the direct gas impingement operated locked bolt action of the MK18. These factors, in addition to the difference in combustion regime amplitudes of supersonic 5.56x45mm and subsonic 9x19mm, result in a different influence of mechanical weapon noise to the total signature to which bystanders and the shooter is subjected.
As always, it is important to note that momentum transfer, weapon condition (upper receiver fouling), and other factors, can significantly influence bolt closing time. PEW Science urges the reader to exercise extreme caution if using the published bolt closing time to make determinations regarding silencer flow restriction (back pressure) or weapon system kinematics. This type of calculation may provide erroneous results, as the weapon condition at the time of each test is not published data. The time-scale duration showing bolt closing time is only published by PEW Science such that the signature data pedigree may be verified.
The shape, timing, and magnitudes of the early-time pressure pulses and overall shape of the impulse waveforms measured at the muzzle, from shot-to-shot, are relatively consistent. The consistency of the waveform amplitudes highlight the silencer’s overall sound performance consistency at the muzzle after the FRP, as well as the relative consistency of the tested semiautomatic firearm configuration.
PEW Science Research Note 5: Note that the muzzle Suppression Rating of the HUXWRX CASH 9K with the direct thread mount is 45.3 and the shooter’s-ear Suppression Rating is 43.2; which are the in the same zone on the Suppression Rating Dose Chart. This is an unusually balanced performance attribute for submachine gun silencer. The gross suppression of a silencer, as well as its flow rate, influences the holistic signature on the standard HK SP5-A2 weapon system.
6.97.2 Suppression Rating Comparison (Subsonic 9x19mm from the HK SP5-A2)
Figure 5 presents a comparison of the PEW Science Suppression Rating of the HUXWRX CASH 9K with the direct thread mount to that of the Resilient Suppressors RS9 and GSL Phoenix on the HK SP5-A2 system. The standard PEW Science HK SP5-A2 test host weapon system is described in Public Research Supplement 6.85.
Figure 5. Suppression Rating Comparisons of the HUXWRX CA$H 9K with the Resilient Suppressors RS9 and GSL Phoenix on the HK SP5-A2 and SP5K-PDW, Using PEW-SOFT 9x19mm Subsonic Test Data and PEW Science Analysis
The performance of the HUXWRX CASH 9K, in the above context, is significant.
The CASH 9K is slightly quieter than the Resilient Suppressors RS9 (Review 6.90) on the HK SP5-A2, to the shooter, despite being shorter and louder at the muzzle. Although the CASH 9K’s muzzle (bystander) Suppression Rating is a category below that of the RS9, it results in very similar hearing damage risk to the weapon operator as the larger silencer. The CASH 9K possesses a higher flow rate (lower back pressure) than the Resilient Suppressors RS9. This is the same comparison as was made previously between the RS9 and the GSL Phoenix (Review 6.86). It should be noted that the size difference of the three silencers is significant.
The HUXWRX CASH 9K produces a relatively high Suppression Rating at the shooter’s ear, despite a lower muzzle rating, on the HK MP5 system. The CASH 9K is only 5.2 inches long in the direct thread configuration. PEW Science postulates that the limits of signature suppression at the shooter’s ear on the HK MP5 system may only be exceeded by further end cap standoff while maintaining high flow rate (low back pressure). This postulation is limited to the subsonic pistol cartridge combustion regime with muzzle-mounted silencers.
The PEW Science Suppression Rating quantifies inner ear damage risk. Human perception of sound may, or may not, always correlate. More detailed information regarding this phenomenon is presented periodically in PEW Science Member Research Supplements.
The signature to which the shooter’s ear is subjected is a function of both ejection port and muzzle signature. When the silencer’s endcap is in closer proximity to the shooter, the severity is increased. The coalescing of the ejection port overpressure with the primary muzzle blast may exacerbate the severity of the signature at the shooter’s head position. It is not ejection port signature, alone, that dictates the signature measured at the shooter’s head position.
Although the published suppressed HK SP5 dataset is limited, two significant conclusions can be drawn from this data and analysis:
The roller-delayed blow back MP5 operating system is still a blow back system. The delay, even when maximized with the 80-deg locking piece, still does not completely eliminate gas sensitivity during suppressed use. Silencer back pressure still influences the signature at the shooter’s ear on this suppressed weapon system.
The Flow-Baffles in the HUXWRX CA$H 9K significantly reduce back pressure. Their suppression performance in the subsonic pistol cartridge regime is notable, and the MP5 is gas sensitive enough for their back pressure reduction to have efficacy. This is still the case, despite the silencer’s short length and more severe muzzle signature.
The above two conclusions are significant. Further study of the suppressed roller-delayed blow back system is a subject of future PEW Science research.
6.97.3 Review Summary: HUXWRX CASH 9K on the HK SP5 9x19mm Subgun with 8.9-in barrel
When paired with the 8.9-in barrel HK SP5-A2 with 80-deg locking piece and fired with Speer Lawman 147gr, the HUXWRX CASH 9K mounted with the direct thread mount achieved a composite Suppression Rating™ of 47.8 in PEW Science testing. The Semiautomatic Pistol (Handgun) performance of the HUXWRX CA$H 9K on the HK P30L is detailed in Sound Signature Review 6.96, in which it achieved a Suppression Rating of 45.3. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
PEW Science Subjective Opinion:
The HUXWRX CA$H 9K is a compact 9mm pistol silencer that exhibits extremely low backpressure. At 7.5 ounces and 5.2 inches long in the direct thread configuration, the CASH 9K is lighter and smaller than many other 9mm submachinegun silencers on the current market, while also exhibiting superior sound signature suppression to the shooter, using the HK MP5. The holistic design and performance of the CA$H 9K is notable, especially for its size.
The backpressure-reducing features of the HUXWRX CASH 9K are somewhat similar to its rifle silencer counterparts from HUXWRX / OSS. However, due to the combustion pressure and duration produced by many pistol cartridges, more conventional features are present in HUXWRX’s “Flow-Baffles” than in their “Flow-Through” rifle internal designs. Nonetheless, the Flow-Baffle technology does show efficacy in the subsonic pistol cartridge combustion regime, as evidenced by the data and analysis in this test report. PEW Science postulates that systems most sensitive to silencer back pressure stand to gain the most performance benefit from this technology. Semiautomatic and automatic submachineguns often exhibit significant “port pop” to the shooter; this phenomenon is significantly reduced by silencers like the HUXWRX CASH 9K, the Resilient Suppressors RS9, and over-bored or short pistol caliber silencers. Increased flow rate (reduced back pressure) of silencers used on semiautomatic submachineguns (or “PCCs;” pistol caliber carbines) is paramount to signature reduction performance to the weapon system operator.
Users should note that bystanders will be subjected to a higher hearing damage risk with the CASH 9K than with some other high-performance centerfire pistol caliber silencers. This difference in muzzle Suppression Rating is a consequence of the CASH 9K’s flow rate and very compact size.
HUXWRX states that the CASH 9K is rated for fully-automatic fire with the cartridges of interest (9mm and 300 BLK subsonic). Although PEW Science has not evaluated the durability of the CASH 9K, its high flow rate is most likely a welcome performance attribute for its use on such systems. It is postulated that its stainless steel baffles are also resilient enough for this use.
Disassembly of the CASH 9K with the included tool is relatively simple; the tool can be used to remove both the included direct-thread mount and the silencer’s end cap. The use of other mounting systems is possible. Successful operation of the CASH 9K on a semiautomatic handgun is possible with the rear piston retainer and piston from a SilencerCo Omega 9K, for example.
Of particular note is the small size and relatively light weight of the HUXWRX CASH 9K. At 7.5 ounces and 5.2 inches long with the direct thread mount, its performance in the design envelope is notable.
In this review, the HUXWRX CASH 9K performance metrics depend upon suppressing a subsonic centerfire pistol cartridge on a roller-delayed blowback submachinegun. While the sound signature of such cartridges can be suppressed to levels that may result in the desire of the shooter and bystanders to not wear hearing protection, PEW Science encourages the reader to remain vigilant with regard to all subsonic pistol cartridge suppression claims. The gas volume and combustion products created by firing a subsonic centerfire pistol cartridge such as 9x19mm are still significant; the measured pressure and impulse magnitudes, and their durations, illustrate this fact. Silencer performance on automatic (reciprocating) weapons depends on many factors. Weapon configuration may significantly influence total suppressed small arm system performance.
The hearing damage potential of subsonic submachinegun 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.
