SSS.6.86 - GSL Phoenix and the Heckler and Koch SP5 9x19mm Subgun

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GSL Phoenix on the HK SP5 9x19mm Subgun with 8.9-in barrel

The Phoenix is designed and manufactured by GSL Technology. It is a 9mm centerfire submachinegun silencer, intended to suppress the 9x19mm NATO cartridge from barrels of any length. The Phoenix is an updated version of the legacy MK-9K submachinegun silencer. It has a 2-inch diameter and is 7.3 inches long. The silencer may be attached to the host weapon with a variety of mounting options, including a variety of fixed-thread mounts, Sig MPX, CZ Scorpion, UZI, and Micro UZI dedicated weapon mounts, as well as a 3-lug mount to interface with standard Heckler and Koch 9mm barrel lugs. With the attached 3-lug mount, as tested, the length of the silencer is 8.5-inches, though the length added to the weapon is closer to the length of the silencer body due to the nature of the 3-lug mount design. The silencer’s tube, user-serviceable coaxial core, and machined baffles, are all constructed from aluminum. The silencer weighs 17.9 ounces with the 3-lug mount, as tested. The Phoenix can be obtained from GSL Technology.

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-GSL-028-001-22. Therefore, data pertaining to the Phoenix in this Sound Signature Review is published with the express written permission of GSL Technology, Inc.

This Sound Signature Review contains single-test results using the GSL Phoenix with the 3-lug 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 6.86.1 contains the Phoenix test results and analysis.

  • Section 6.86.2 contains Suppression Rating comparisons of the Phoenix with unsuppressed subsonic 9mm ammunition fired from the Heckler and Koch SP5-A2.

  • Section 6.86.3 contains the review summary and PEW Science subjective opinions.

Engineering Peer Review Note (Errata): Since this article was published, internal engineering review and external engineering peer review revealed an error in certain conclusions concerning weapon kinematics described in the Member article (Section 6.86.1.2). The error has been corrected.

Summary: When paired with the 8.9-in barrel HK SP5-A2 with 80-deg locking piece and fired with Speer Lawman 147gr, the GSL Phoenix mounted with the 3-lug mount achieved a composite Suppression Rating™ of 62.4 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

6.86.1 GSL Phoenix Sound Signature Test Results

A summary of the principal Silencer Sound Standard performance metrics of the Phoenix tested with the 3-lug 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. 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. GSL Phoenix Sound Metric Summary

 

6.86.1.1 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 GSL Phoenix 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. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Pressure Signature

Fig 1b. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Sound Pressure Signature

Figure 2a. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature

Figure 2b. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Muzzle Sound Impulse Signature

The GSL Phoenix is a high performance submachinegun silencer. Additional performance context will be presented in future PEW Science Sound Signature Reviews. The reader should note the following:

  1. 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).

  2. The muzzle pressure signature from the HK SP5-A2 is significantly suppressed with the Phoenix, as shown in Figure 1b.

  3. The first-round-pop (FRP) from the Phoenix is significantly suppressed to bystanders; an increased risk of hearing damage to bystanders during the first shot is effectively nullified, in accordance with PEW Science inner ear modeling.

PEW Science Research Note 1: Although the effects of FRP through the Phoenix are nullified to observers, 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: 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 3: 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 4: Note that the muzzle Suppression Rating of the GSL Phoenix with the 3-lug mount is 62.3 and the shooter’s-ear Suppression Rating is 41.3; which are significantly different zones on the Suppression Rating Dose Chart. 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 below.

6.86.1.2 SOUND SIGNATURES AT SHOOTER’S EAR

Real sound pressure histories from the same 6-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 6 shots are shown in Figure 3. The primary sound signature history is shown in Figure 3a. A zoomed-in timescale is displayed in Figure 3b, in the region of peak sound pressure for Shot 1, Shot 2, and Shot 3. The real sound impulse (momentum transfer potential) histories at the ear from the same 6-shot test are shown in Figure 4. Again, full and short timescales are shown.

Figure 3a. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Ear Sound Pressure Signature

Figure 3b. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Ear Sound Pressure Signature, Short Time Window

Figure 4a. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Ear Sound Impulse Signature

Figure 4b. GSL Phoenix subsonic 9x19mm HK SP5-A2 Semiautomatic Subgun Ear Sound Impulse Signature Peaks

The sound signatures measured at the shooter’s ear from a suppressed roller-delayed blowback submachine gun are complex. However, there are key waveform features that allow for strict interpretation of various events occurring during the gunshot, and their contribution to the overall signature.

PEW Science Research Note 5: Two primary factors differentiate the shooter’s-ear waveform signature compositions from a supersonic 5.56x45mm NATO automatic gas-operated rifle (the MK18) and a subsonic 9x19mm roller-delayed blowback submachine gun (the HK SP5 / MP5):

  1. Overall combustion event amplitude and duration.

  2. Weapon system kinematics; specifically lock time.

The time between combustion initiation and significant pressure pulse presented to the shooter’s ear from that combustion (prior to any gas from the silencer’s end-cap having time to reach the shooter) is relatively short. The time regime may be examined in pressure space in Figure 3b and occurs from approximately 26.6 ms at initiation, peak internal combustion at approximately 27 ms, with a primary shock at approximately 27.2 ms; all three in less than a millisecond, total. The same phenomenon is observed in impulse space in Figure 4b. It is important to note that these events also occur in the unsuppressed firing of the HK MP5 system; they are characteristic of the host. Clear delineation of these events are possible due to (1) and (2), above, and through the use of PEW-SOFT. Note that the early-time combustion pulse from Shot 2 is significantly higher than that from other shots (Figure 3b). This phenomenon did not adversely influence the test results, but is worth noting due to the presented signature.

PEW Science Research Note 6: Following the above, the sequence of events in the measured signatures become exceedingly complex. Depending upon the silencer’s flow rate and suppression performance, the shooter’s ear is impacted by coalescing waves from multiple sources. The GSL Phoenix has such significant muzzle suppression, that the propagation of muzzle blast is suppressed and its impact to the shooter significantly delayed (see notes in Fig. 3b). The latent components of the primary suppressed muzzle blast event coalesce with the signature originating from the bolt carrier group’s unlocking mechanics*. The magnitude of this event may be influenced by silencer back pressure. Internal PEW Science research is ongoing.

*PEW Science Research Peer Review Notes: Internal engineering reviews and external engineering peer reviews have been conducted, focusing on weapon system kinematics related to these late-time events. The roller movement and trunnion disengagement events are most likely the contributors in this time regime. Note that the bolt head is able to move prior to roller disengagement. Figure 3b and Figure 4b have been updated since the original review publication to reflect these kinematics. Late-time event kinematics, such as cartridges being stripped from the magazine and the bolt returning to battery have also been verified (Figure 1a, 85 ms and Figure 3a, 83 ms).

Due to the relatively low amplitude and duration of subsonic 9x19mm combustion compared with supersonic 5.56x45mm combustion, the influence of the above signature factors on the holistic system signature, especially to the shooter, is more significant.

PEW Science Research Note 7: Unlike the case at the muzzle and to bystanders, the FRP from the GSL Phoenix at the shooter’s ear on this weapon system is not as significantly suppressed. Although the postulated hearing damage risk to the shooter from FRP is not severe, it may be approximately 20% more severe than subsequent shots, in accordance with PEW Science inner ear modeling.

6.86.2 Suppression Rating Comparison (Subsonic 9x19mm from the HK SP5-A2)

Figure 5 presents a comparison of the PEW Science Suppression Rating of the GSL Phoenix with the 3-lug mount to that of the unsuppressed 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 GSL Phoenix and the Unsuppressed HK SP5-A2, Using PEW-SOFT 9x19mm Subsonic Test Data and PEW Science Analysis

Readers may immediately note the reduction in relative severity between unsuppressed subsonic 9x19mm from the standard HK SP5-A2 weapon system compared with that of previously published unsuppressed supersonic 5.56x45mm from the standard MK18. The difference in both combustion pressure duration, and amplitude, drive the severity differential.

As described in the Member Version of this article, there are various host weapon characteristics, as well as silencer characteristics, that drive the shooter’s ear Suppression Rating lower than the muzzle (bystander) Suppression Rating on this weapon system. The GSL Phoenix is a high performance submachine gun silencer, but it is still subject to weapon system characteristics such as lock time and reciprocation kinematics. Furthermore, its flow rate directly impacts the gas dynamics of the system and influences the holistic signature,

Additional performance context will be presented in future PEW Science Sound Signature Reviews. The reader should note the following:

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 exacerbates 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.

6.86.3 Review Summary: GSL Phoenix 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 GSL Phoenix mounted with the 3-lug mount achieved a composite Suppression Rating™ of 62.4 in PEW Science testing. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.

PEW Science Subjective Opinion:

The GSL Phoenix is a full-size submachinegun silencer that exhibits extremely high suppression performance and is relatively lightweight for its size. The plethora of mounting options, user-serviceability, and performance pedigree spanning decades, are notable. Note that the Phoenix is an updated version of the legacy MK-9K submachinegun silencer.

As the Phoenix is an updated version of the MK-9K, it is therefore a coaxial silencer. However, the Phoenix does possess significantly different internal features; unlike the MK-9K that utilized stamped washers and spacers to form its baffle stack, the Phoenix possesses machined M-baffles within its coaxial core assembly. It is likely that the suppression and gas dynamics from the M-baffle system are more advanced. Testing of the MK-9K and other legacy submachinegun systems is the subject of future PEW Science research.

The GSL Phoenix is designed for the Heckler and Koch MP5 (and thus the semiautomatic SP5 analog). The measured and analyzed performance of the Phoenix on the SP5 is indicative of this design specialty. The performance of the Phoenix on this platform is significant.

Of particular note is the relatively light weight of the Phoenix. At a little over a pound, a full size machine gun silencer of its length and girth is notable. Users should also note that this weight is made possible by its aluminum construction. The Phoenix is user-serviceable; a welcome change from the legacy MK-9K design. However, because the parts are aluminum, care must be take by the user to not damage them during cleaning. PEW Science highly recommends that users follow the manufacturer’s maintenance and care instructions.

Although the GSL Phoenix is constructed of aluminum, it is rated for sustained fully automatic use on submachine gun platforms (9x19mm). It is important to note that the Phoenix is not a rifle silencer and should not be used with rifle cartridges, subsonic 300 BLK notwithstanding.

A plethora of mounting options are available for the Phoenix, including a variety of fixed-thread mounts, Sig MPX, CZ Scorpion, UZI, and Micro UZI dedicated weapon mounts, as well as a 3-lug mount to interface with standard Heckler and Koch 9mm barrel lugs. Of particular note is that the Phoenix 3-lug mount (and therefore all 3-lug mounts like it, which are now ubiquitous) is of the Gregory S. Latka (GSL) design. PEW Science considers it historically significant that the Phoenix silencer and this mount are now present in the Silencer Sound Standard. During internal PEW Science R&D, the so-called “Latka” 3-lug mount is consistently one the most high quality, resilient, and secure 3-lug mounts of its kind across brands on the current market, and does not possesses incompatibility issues on high quality barrels. Other secure 3-lug mounting solutions do exist, namely the so-called “Bixler” 3-lug mount. Evaluation of the Timothy D. Bixler (SCRC) design is the subject of future PEW Science research.

Although the sound suppression performance to bystanders, with the GSL Phoenix, is extreme, care should be take by the weapon operator due to coupled muzzle blast and ejection port signature, as is the case on many, if not all, reciprocating suppressed small arm weapon systems. The Suppression Rating dose chart is intended to help guide users to understand the potential severity in accordance with their own personal risk tolerance.

In this review, the GSL Phoenix 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.