SSS.6.148 - Combat Application Technologies CAT/MOB/A1 and the Heckler and Koch SP5 9x19mm Subgun (Free Version)
/Combat Application Technologies CAT/MOB/A1 on the HK SP5 9x19mm Subgun with 8.9-in barrel
The CAT/MOB/A1 (“MOB” in this report) is designed by Combat Application Technologies (CAT). It is a 36 caliber submachine gun silencer, intended to suppress many cartridges with projectiles appropriately sized to travel through the bore, including 8.6 BLK. It has a 1.6-inch diameter and the silencer core is 7.2 inches long (HUB model) or 7.5 inches long (QD model). The HUB compatible model features 1.375”-24 tpi threading allowing for the installation of a variety of 3rd-party mounting systems and muzzle devices with the silencer. Length of the total system will vary, depending on mount choice. For example, use of the CAT/TSF X, a threaded coupler, will result in a total system length equaling that of the QD version of the silencer. The entirety of the silencer is DMLS (3D-printed) from a proprietary Titanium alloy. The core of the tested QD model silencer weighs 9.1 ounces, while the core of the HUB model weighs 8.3 ounces. The Spooky flash hider and the titanium TSF X adapter used in testing of the HUB compatible model resulted in a total system weight of 12.1 ounces and total system length of 7.5 inches. The CAT MOB 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-CAT-059-001-23. Therefore, data pertaining to the CAT/MOB/A1 in this Sound Signature Review is published with the express written permission of Combat Application Technologies.
This Sound Signature Review contains single-test results using the CAT/MOB/A1 with the Spooky flash hider 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 6.148.1 contains the MOB test results and analysis.
Section 6.148.2 contains Suppression Rating comparisons of the MOB with the PTR VENT 2, Otter Creek Labs Lithium, HUXWRX CA$H 9K, Resilient Suppressors RS9, and GSL Phoenix fired on the Heckler and Koch SP5-A2.
Section 6.148.3 contains the review summary and PEW Science laboratory staff technical 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 CAT/MOB/A1 mounted with the Spooky flash hider achieved a composite Suppression Rating™ of 65.3 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
6.148.1 CAT/MOB/A1 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the CAT MOB tested with the Spooky flash hider 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 public PEW Science testing, research, and development with a membership, here. State-of-the-art public firearm sound signature testing and research conducted by PEW Science is supported by readers like you.
Table 1. CAT/MOB/A1 Sound Metric Summary
6.148.1.1 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 submachine guns 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 CAT MOB are shown in Figure 1a. The sound signatures of Shot 1 and Shot 2 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 4.
Fig 1a. CAT/MOB/A1 subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Pressure Signature
Fig 1b. CAT/MOB/A1 subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Sound Pressure Signature
Figure 2a. CAT/MOB/A1 subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature
Figure 2b. CAT/MOB/A1 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature
The signatures measured from the CAT MOB on this platform exhibit characteristics unlike those seen in previous HK SP5/MP5 platform testing. Like other high performance silencers, the CAT MOB significantly suppresses muzzle blast. However, unlike those other silencers, early-time pressure blowdown is expedient and gas momentum propagation is throttled, with almost no measurable first-round-pop (FRP). There are clear signature features illustrating these performance attributes and staged gas propagation behavior, including:
Consistent precursor and coupled jet flow (Fig. 1b).
Rapid rise to maximum free field positive phase impulse (Fig. 2a).
Expedient impulse decay with subsequent throttling (Fig. 2b). The region of positive phase impulse accumulation above nominal levels is of relatively short duration.
In addition to the performance attributes above that result in extremely high gross suppression performance, the early time flow rate of the CAT MOB results in enhanced back pressure reduction on this host weapon. Specific details of the phenomenology characterized at the operator’s location are presented in the full Member Version of this article. These performance factors are facilitated by a technology that shares some similarities with that of CAT SURGE BYPASS. The technology implemented in the MOB is CAT DiVerge.
PEW Science Research Note 1: CAT DiVerge technology, like the CAT SURGE BYPASS and SNIPER2 technologies, is contained within CAT’s SkyNET design vectors, each utilized to achieve different performance characteristics on the requisite weapon system platforms. Although both SURGE BYPASS and DiVerge technologies excel with high pressure input and reduce the propensity for system over function through the use of elevated early time flow rate, DiVerge technology is implemented in silencers like the MOB to not only reduce back pressure, but to simultaneously provide extreme suppression performance, shortening durations of positive phase impulse accumulation above certain design thresholds in the pressure field. Classified as another hybrid technology in the PEW Science taxonomy, CAT DiVerge designs are optimized for the lower combustion pressures of centerfire pistol cartridges. In the CAT MOB, the DiVerge technology regulates the varied low pressure conditions throughout each stage of the silencer, for applications in which maximum signature suppression is paramount. Flow rate is maintained in early time, with significant external gas momentum throttling in a consistent time regime.
PEW Science Research Note 2: As discussed in the above description of CAT DiVerge technology, the system implemented in the CAT MOB results in some of the most advanced performance on the HK MP5 submachine gun platform of any silencer tested by PEW Science, to date. Other significantly advanced technologies evaluated on this system by PEW Science include PTR Purposely Induced Porosity (PIP); a technology in which high pressure combustion gasses are forced through a metallic matrix lattice structure to increase surface area contact and turbulence, both of which help achieve the goal of a high degree of heat transfer efficiency in a short time regime. The performance of the PIP technology was showcased in the testing and analysis report of the PTR VENT 2 silencer on the MP5 (6.131).
Whereas the PIP technology produces the above performance benefits combined with a high early-time flow rate, reducing back pressure, there are two key differentiators between the behavior of PIP and DiVerge technologies apparent in analysis of PEW Science laboratory test data:
Like HUXWRX Flow-Through technology, the performance potential and efficiency of PTR PIP is directly proportional to combustion duration when implemented for low pressure suppression. This is one of the reasons those technologies must be combined with conventional baffle geometries for low pressure applications. Below a certain pressure threshold in PIP, which occurs during the time regime of low pressure combustion propagation of the centerfire 9mm pistol cartridge, heat transfer efficiency drops through the lattice and increased turbulence through conventional geometry is relied upon to continue the cycle. This phenomenon is accompanied by longer blowdown and less potential for later time flow rerouting. CAT DiVerge technology in the MOB is not subject to these limitations, as gas stage progression is continuous with largely the same mechanisms from early time to complete blowdown. Both PIP and DiVerge technologies excel in low pressure suppression. DiVerge technology appears to exceed the performance of PIP in PEW Science laboratory evaluations, to date.
Backpressure reduction from PIP is largely due to increased early-time flow rate through lattice structure venting. This advanced flow management results in significant hazard reduction to the weapon operator on multiple weapon platforms, including the HK MP5 system. However, as the lattice structure rapidly heats, latent expansion is somewhat inhibited. Furthermore, it is postulated that there is a maximum flow rate through the lattice that is reached relatively early in time. The CAT DiVerge technology is not encumbered by the same type of heat transfer mechanisms, nor flow rate limitations. Because it is a staged pressure management technology, DiVerge-equipped systems like the CAT MOB are able to increase early-time flow rate to a greater degree, and keep the flow rate elevated for a longer duration while simultaneously throttling downstream gas momentum. This enhanced pressure distribution results in a different duration profile of system backpressure, and when applied to MP5 suppression, produces unprecedented hazard reduction to the weapon operator and bystanders.
The principal combination of mechanisms allowing the CAT MOB to achieve extremely high total pressure field suppression performance on the semiautomatic MP5 is high early time flow rate with pressure stagnation relief that is simultaneously continued through multiple stages resulting in consistent throttling to atmosphere. The CAT MOB provides extreme muzzle suppression while also reducing the impulsiveness of the roller-delayed-blowback unlocking mechanics. This behavior is unprecedented and detailed in the Member version of this review. Based on this evaluation and further internal testing of multiple system variants, PEW Science laboratory staff hold the opinion that that the DiVerge technology implemented in the CAT MOB is sufficiently advanced such that it may be classified as “next generation” in the taxonomy.
PEW Science Research Note 3: The gross suppression performance of the CAT MOB on this platform is only approached by the PTR VENT 2 and GSL Phoenix (6.86) in the current research pedigree. The CAT MOB exceeds the suppression performance of both the VENT 2 and Phoenix and does so by a rather significant margin; the reduction in hazard to the weapon operator is significant. The CAT MOB is shorter than the PTR VENT 2, smaller in diameter than the Phoenix, and if used with a direct-thread mount, also lighter than both of those silencers. In totality, the CAT MOB provides the highest performance for the design envelope of any silencer tested on the MP5 system, to date.
There do exist other silencers that also possess high flow rates that have demonstrated efficacy on this platform, either in early time or in their gross gas dynamics. Such silencers include the Resilient Suppressors RS9 (6.90) and the HUXWRX CA$H 9K (6.97). Those two silencers also significantly reduce operator hazard on this weapon system, though not to the degree of the CAT MOB, and not with comparable overall suppression performance. In late time, the signatures from those two silencers are significantly more noticeable to the operator. To bystanders, those two silencers are considerably louder than the CAT MOB. The Otter Creek Labs Lithium (6.102) does increase suppression performance over those silencers that are smaller than the MOB, though it does so with higher back pressure, increased hazard to the weapon operator, and significant FRP. Like the larger GSL Phoenix, the Lithium is a conventional baffle silencer.
The CAT MOB also completely masks FRP to bystanders on this weapon system.
PEW Science Research Note 4: 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 5: 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 and alpha parameter 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 or M4A1. 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 6: Note that the muzzle Suppression Rating of the CAT MOB with the flash hider mount is 65.1 and the shooter’s-ear Suppression Rating is 50.6; which are the different zones on the Suppression Rating Dose Chart. This demonstrates a typical performance attribute for silencers fielded on submachine guns. The gross suppression of a silencer, as well as its flow rate, influences the holistic signature on the standard HK SP5-A2 weapon system.
The signatures measured at the shooter’s ear are presented in the full Member Version of this article.
6.148.2 Suppression Rating Comparison (Subsonic 9x19mm from the HK SP5-A2)
Figure 5 presents a comparison of the PEW Science Suppression Rating of the CAT MOB with the flash hider mount to that of the PTR VENT 2, OCL Lithium, HUXWRX CA$H 9K, Resilient Suppressors RS9, and GSL Phoenix on the HK SP5-A2 system. The standard PEW Science HK SP5-A2 test host weapon system is described in Public Research Supplement 6.85.
Figure 5. Suppression Rating Comparisons of the CAT/MOB/A1 with the PTR VENT 2, Otter Creek Labs Lithium, HUXWRX CA$H 9K, Resilient Suppressors RS9, and GSL Phoenix on the HK SP5-A2, Using PEW-SOFT 9x19mm Subsonic Test Data and PEW Science Analysis
The CAT MOB induces a lower hearing damage risk potential to bystanders than does the PTR VENT 2 (6.131) or GSL Phoenix (6.86). When compared to the Otter Creek Labs Lithium (6.102) and Resilient Suppressors RS9 (6.90), the CAT MOB is significantly quieter.
Both the HUXWRX CA$H 9K (6.97) and the the RS9 possess very high effective flow rates for this platform and reduce operator hazard from ejection port blast, significantly. As previously discussed, the VENT 2 also possesses a very high flow rate and not only reduces ejection port blast, but significantly suppresses muzzle blast. In the case of the CAT MOB, not only is backpressure reduced to the degree such that ejection port blast is minimized, mechanical noise is also reduced. Those factors, along with extremely low muzzle blast load coalescence, allow an MP5 system equipped with a CAT MOB to reach a Suppression Rating at the shooter’s ear entering the 50-zone. This level of operator hazard reduction is unprecedented on the MP5 weapon system in PEW Science testing. Because the muzzle Suppression Rating with the CAT MOB is also very high, the comparison of total pressure field suppression between this group of silencers spans a relatively large performance differential. The difference in overall hazard reduction from a CAT MOB-equipped MP5 to a CASH 9K-equipped system, in multiple environments, is extremely significant. The two performance cases are not comparable.
The CAT MOB produces a gross sound field on this weapon system quieter than a PTR VENT 2 and GSL Phoenix in a more competitive design envelope, which is notable.
PEW Science Research Note 10: 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. As noted in the full Member Version of this article, mechanical noise factors also play a role in shooter hazard.
As the published suppressed HK MP5/SP5 dataset continues to grow, two significant conclusions drawn in previous articles once again hold true in 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, early-time venting in the Resilient Suppressors RS9, and PIP technology in the PTR VENT 2, all significantly reduce back pressure. The suppression performance of those three silencers to the shooter in the subsonic pistol cartridge regime is notable, and the MP5 is gas sensitive enough for their back pressure reduction to have efficacy. The data presented with the CAT MOB in this article further illustrates the benefit of high flow rate designs, even on the pistol-caliber roller-delayed blow back system, and also illustrates the degree to which advanced hybrid technologies may further enhance MP5 suppression performance to both the operator and bystanders.
Further study of the suppressed roller-delayed blow back system is a subject of internal PEW Science research.
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.
6.148.3 Review Summary: CAT/MOB/A1 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 CAT MOB mounted with the Spooky flash hider mount achieved a composite Suppression Rating™ of 65.3 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 CAT/MOB/A1 (CAT MOB) is a lightweight and highly advanced 36 caliber submachine gun silencer that exhibits extreme sound signature suppression performance. For its size and weight envelope, the MOB’s performance is even more significant. Notably, the CAT DiVerge technology in the MOB silencer appears to regulate the varied low pressure conditions throughout each stage of the silencer, reducing backpressure while simultaneously achieving maximum signature suppression. The CAT MOB exhibits the most advanced submachine gun suppression performance evaluated by the PEW Science laboratory, to date.
CAT DiVerge technology, like the CAT SURGE BYPASS and SNIPER2 technologies, is a part of CAT’s SkyNET design vectors, each utilized to achieve different performance characteristics on the requisite weapon system platforms. Although both SURGE BYPASS and DiVerge technologies excel with high pressure input and reduce the propensity for system over function through the use of elevated early time flow rate, DiVerge technology is implemented in silencers like the MOB to not only reduce back pressure, but to simultaneously provide extreme suppression performance, shortening durations of positive phase impulse accumulation above certain design thresholds in the pressure field. Classified as another hybrid technology in the PEW Science taxonomy, CAT DiVerge designs are optimized for the lower combustion pressures of centerfire pistol cartridges. In the CAT MOB, the DiVerge technology regulates the varied low pressure conditions throughout each stage of the silencer, for applications in which maximum signature suppression is paramount. Flow rate is maintained in early time, with significant external gas momentum throttling in a consistent time regime.
The gross suppression performance of the CAT MOB on this platform is only approached by the PTR VENT 2 and GSL Phoenix. The CAT MOB exceeds the suppression performance of both the VENT 2 and Phoenix and does so by a rather significant margin; the reduction in hazard to the weapon operator is significant. The CAT MOB is shorter than the PTR VENT 2, smaller in diameter than the Phoenix, and if used with a direct-thread mount, also lighter than both of those silencers. In totality, the CAT MOB provides the highest performance for the design envelope of any silencer tested on the MP5 system, to date.
Based on this evaluation and further internal testing of multiple system variants, PEW Science laboratory staff hold the opinion that that the DiVerge technology implemented in the CAT MOB is sufficiently advanced such that it may be classified as “next generation” in the taxonomy.
The CAT MOB is offered with so-called HUB universal mount threading at the proximal end, and also as a “QD” model. Overall Composite Suppression Rating performance of the two systems is shown to vary nominally in PEW Science internal testing, when controlling for total system length. It is possible that direct-thread mounts further enhance the suppression performance of the MOB system. Further research is needed. Although the CAT MOB may be used with a variety of cartridges, such as 8.6 BLK, the user is encouraged to contact the manufacturer for recommended system applicability.
Users should note that, in general, the sparking performance of Titanium silencers may vary. On the 9mm MP5 system, sparking under both visual and infrared observation from the Titanium CAT MOB has been demonstrated to be extremely minimal. This is due to both the DiVerge technology as well as the lower pressures and temperatures of the 9mm cartridge when compared to that of rifle cartridges.
In addition to fixed-barrel weapons, it is possible that the CAT MOB may be used on semiautomatic handguns. The use of a silencer on such a weapon, for example, a modified tilting-barrel Browning action, may often be accomplished through the use of an inertial decoupler assembly. PEW Science has not evaluated the CAT MOB in such a configuration. In general, PEW Science recommends the user contact both the silencer manufacturer and weapon manufacturer prior to creating and operating a suppressed weapon system from these components.
In this review, the CAT MOB performance metrics depend upon suppressing a subsonic centerfire pistol cartridge on a roller-delayed blowback submachine gun. 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 submachine gun 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.
