SSS.6.110 - Maxim Defense DSX and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)
/Maxim Defense DSX on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The DSX is designed and manufactured by Maxim Defense. It is a 5.56mm centerfire rifle silencer, intended to suppress the 5.56x45mm cartridge on barrels as short as 5.5 inches in length. The DSX-D (the direct thread model tested) has a 1.75-inch primary diameter and is 7.9 inches in length from distal wrench features to the base of the direct thread mount. The DSX-M is identical to the DSX-D other than the capability for its direct thread mount to be removed and fitted with universal so-called HUB mounting solutions. Without the direct thread mount installed, the DSX-M is 7.25 inches long. The silencer’s core is monolithic 17-4 stainless steel, and the unit is user serviceable; a retention spring is included that helps to prevent unintended system disassembly during use. The mount, as well as the tube, are Grade 5 titanium. The DSX-D silencer weighs 22.2 ounces, as tested. The DSX-M, without its direct thread mount installed, weighs 20.5 ounces. The DSX silencers may be obtained from Maxim Defense.
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-Maxim-049-001-22. Therefore, data pertaining to the DSX in this Sound Signature Review is published with the express written permission of Maxim Defense Industries, LLC.
This Sound Signature Review contains single-test results using the Maxim Defense DSX direct thread mounted on the MK18 Automatic AR15 rifle, chambered in 5.56x45mm NATO with a 10.3-inch barrel. Federal XM193 55gr ammunition was used in the test. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Section 6.110.1 contains the DSX test results and analysis.
Section 6.110.2 contains Suppression Rating comparisons of the DSX with dedicated 223 and 30 caliber silencers on the current market, including the Thunder Beast Dominus, KAC 5.56 QDC, CGS SCI-SIX, Dead Air Nomad-30, YHM Turbo T2, Dead Air Sandman-S, HUXWRX FLOW 556k, Energetic Armament ARX, KAC QDSS-NT4, Rugged Razor556, Otter Creek Labs Polonium and Polonium-K, Surefire SOCOM556-RC2, HUXWRX HX-QD 556 and HX-QD 556k, Q Trash Panda, CGS Helios QD, SilencerCo Saker 556, Rugged Razor762, and others.
Section 6.110.3 contains the review summary and PEW Science subjective opinions.
System Note: The Maxim Defense DSX has also been evaluated with the Maxim Defense Suppressed Upper Receiver Group (SURG). SURG systems are often fielded by end users requiring an optimized upper receiver system paired with a silencer. The evaluated SURG system is different than the standard MK18, despite having the same barrel length. Details of this testing and analysis are provided in Review 6.111 - Maxim Defense DSX SURG. A high level comparison of DSX MK18 and DSX SURG performance is also provided in Section 6.110.2 of this review. Review 6.111 contains a significantly detailed comparative case study for PEW Science Members.
Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Maxim Defense DSX achieved a composite Suppression Rating™ of 38.8 in PEW Science testing.
When incorporated into the Maxim Defense 10.3-in barrel SURG system and fired with Federal XM193, the Maxim Defense DSX achieved a composite Suppression Rating™ of 39.8 in PEW Science testing (Review 6.111).
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
6.110.1 Maxim Defense DSX Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the DSX 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. Maxim Defense DSX Sound Metric Summary
6.110.1.1 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 locked back on the follower of the empty magazine. 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 DSX 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 6-shot test are shown in Figure 2a. In Figure 2b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shot 2 and Shot 3.
Fig 1a. Maxim Defense DSX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Maxim Defense DSX 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. Maxim Defense DSX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Maxim Defense DSX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The Maxim Defense DSX exhibits a relatively low gross flow rate, despite its relatively large volume. The sound suppression performance at the muzzle, in the free field, is significant. Consistent initial jetting is noted followed by gradual amplitude increase to eventual peak (Fig 1b). Note the rate of positive phase impulse accumulation in Fig 2a is relatively low. These signature features are indicative of silencers that restrict flow and that may exhibit significant signature suppression, depending upon frequency and phase components. In the case of the DSX, it exhibits the highest Suppression Rating at the muzzle on the MK18 published in the current dataset; slightly higher than that of the Otter Creek Labs Polonium (6.75). It should be noted that the DSX is larger than the Polonium.
PEW Science Research Note 1: The first-round-pop (FRP) from the DSX is noted in both pressure space (Figure 1) and impulse space (Figure 2). It is interesting to note that the FRP is postulated to be extremely minimal to bystanders, relative to subsequent shots, in accordance with PEW Science inner ear modeling. The consistency of the impulse accumulation histories in Fig 2a are also notable, post-FRP.
PEW Science Research Note 2: One of the reasons for the high degree of consistency noted in the signatures is the silencer’s dedicated bore aperture for the cartridge. The Maxim Defense DSX was designed around the M855 5.56x45mm cartridge. Larger bores are still able to produce consistent signatures, but it is more challenging, depending on the technology implemented in the silencer. An example of this challenge displayed in test data and analysis can be seen in test reports featuring silencers such as the Rugged Razor762 (6.58), the Energetic Armament ARX (6.82); the Rugged Razor556 (6.76); the Q Trash Panda (6.61), and the Dead Air Sandman-S (6.92); all display erratic behavior. Less erratic flow rate, despite an even larger over-bore, is possessed by silencers with alternate flow geometry, like the CGS Helios QD (6.66). This silencer is also significantly over-bored, but possesses coaxial flow paths that may be accessed early in its core geometry.
Typically, as a rifle silencer’s bore becomes smaller, flow rate decreases, all other things equal. However, the flow may be somewhat restricted overall, depending on baffle geometry.
PEW Science Research Note 3: The DSX suppresses overpressure amplitude significantly in early time, and although it possesses a relatively low gross overall flow rate, it jets gas extremely consistently not only from shot to shot, but during each shot. The jetting in each shot is relatively smooth over the time window (ref. Fig 2b). Despite the significantly prolonged positive phase, the gross signature severity is lower than typical for its measured free field peak overpressure and impulse. This is most likely a function of overall amplitude and consistency, resulting from generous interior expansion volumes in the monolithic core, coupled with dedicated bore aperture. This behavior results in a signature, on the MK18, that is less severe at the muzzle and relatively less severe to the operator when compared to silencers with similar gross flow rates. Muzzle signature contributes significantly to operator hazard level, regardless of weapon system.
PEW Science Research Note 4: As in all semiautomatic AR15 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 77 ms in Figure 1a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 does not display this event due to the bolt remaining open after the sixth and final round is fired from the magazine.
PEW Science Research Note 5: The closing time of the MK18 bolt is directly related to the flow restriction of a silencer for a given 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. However, PEW Science has also determined that the indicator is unreliable upon upper receiver fouling. Sound signatures are not influenced by this fouling, as these kinematics occur in late time, after gas venting to atmosphere. 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 automatic rifle firearm configuration.
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 6: Note that the muzzle Suppression Rating of the Maxim Defense DSX is 38.6 and the at-ear Suppression Rating is 22.0; a lower zone on the Suppression Rating Dose Chart. The lower flow rate (higher back pressure) of the Maxim Defense DSX contributes to a more severe ejection port signature, increasing the overall severity of the signature on the standard MK18 weapon system. This phenomenon also occurs with the YHM Turbo T2, the SilencerCo Saker, and the full-size Polonium on the MK18, albeit more severely. The DSX’s muzzle signature is less severe than that of many silencers, to the shooter, on the MK18. Despite this advantage, caution should be exercised by the weapon operator. Note that Maxim Defense produces a dedicated SURG system that is tuned for use with the DSX. That system has been tested and analyzed in Review 6.111.
6.110.2 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 6 presents a comparison of the PEW Science Suppression Rating of the Maxim Defense DSX to that of other rifle silences on the MK18 automatic AR15 rifle. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Figure 6. Suppression Rating Comparisons of the Maxim Defense DSX and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 6 presents the detailed PEW Science Suppression Ratings, computed at the muzzle and ear, for the listed silencers. The Suppression Rating is a holistic parameter that captures human inner ear damage risk potential from a measured impulsive overpressure signature. The parameter may be used with the dose chart at the beginning of this report.
When examining the relative performance of the silencers presented above, the Maxim Defense DSX is shown to posses a less severe muzzle signature than all of the other silencers shown in the current dataset, on the standard MK18 weapon system. The DSX’s Suppression Rating to bystanders is similar to that of the Otter Creek Labs Polonium (6.75). This degree of muzzle suppression on the standard MK18 is significant; for the Suppression Rating to approach the so-called 40-zone from a 10.3 inch barrel 5.56x45mm weapon system is notable. To illustrate the relative severity of the signatures of dedicated 5.56x45mm silencers like the DSX, there also exist dedicated 5.56 silencers that produce significantly more severe muzzle signatures. Such silencers include the Energetic Armament ARX (6.82); a silencer with a signature on the MK18 that may be considered hazardous to bystanders, even for relatively low dose exposure, compared to that from the Maxim Defense DSX. The suppressed MK18 weapon system can produce significantly different hazards to personnel, depending on the silencer used.
PEW Science Research Note 8: It is interesting to note that despite the high degree of muzzle suppression, the Maxim Defense DSX exhibits a Suppression Rating at the shooter’s ear on par with that of the Surefire SOCOM556-RC2 (6.52). This is due to flow rate; although the DSX possesses more overall gross flow restriction, it also suppresses more at the muzzle. The flow restriction does induce a greater ejection port signature contribution, dropping the level of protection at the shooter’s ear on the MK18, but not severely compared to most dedicated-bore 5.56 silencers.
The Maxim Defense DSX has also been evaluated with the Maxim Defense SURG (Suppressed Upper Receiver Group). SURG systems are often fielded by end users requiring an optimized upper receiver system paired with a silencer. The evaluated SURG system is different than the standard MK18, despite having the same barrel length. Details of this testing and analysis are provided in Review 6.111 - Maxim Defense DSX SURG. A high level comparison of DSX MK18 and DSX SURG performance is also provided in Figure 7, below.
Figure 7. Suppression Rating Comparisons of the Maxim Defense DSX on the MK18 and SURG, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
As shown in Figure 7, the Suppression Rating at the shooter’s ear may be significantly influenced by the ejection port signature from the MK18; all other things equal. For more details on dedicated SURG testing and analysis with the DSX, please see Review 6.111. That publication directly illustrates the benefit of “tuning” an AR-15 weapon system for a silencer. It is important to note that not all silencers will possess the same increase in shooter’s ear Suppression Rating from weapon tuning. Signature at the operator’s head is a function of both muzzle and ejection port signatures from the AR-15 weapon system.
6.110.3 Review Summary: Maxim Defense DSX on the MK18 5.56x45mm AR15 with 10.3-in Barrel
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Maxim Defense DSX achieved a composite Suppression Rating™ of 38.8 in PEW Science testing. When incorporated into the Maxim Defense 10.3-in barrel SURG system and fired with Federal XM193, the Maxim Defense DSX achieved a composite Suppression Rating™ of 39.8 in PEW Science testing (Review 6.111). As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
PEW Science Subjective Opinion:
The Maxim Defense DSX is a full-size 5.56 machine gun rated rifle silencer. With a manufacturer-rated barrel length minimum of 5.5 inches for fully automatic firing schedules, the DSX is appropriate for extreme duty use. The signature suppression performance of the silencer on the short-barrel MK18 is very high at the muzzle; however, the silencer is relatively large compared to other dedicated 5.56 silencers. Nonetheless, the performance is significant, and its weight is on par with that of some other duty silencers. It should be noted that an identical version of the silencer is offered with a modular rear mount interface.
The Maxim DSX possesses an asymmetrical monolithic steel core. Such silencer internal geometries are colloquially referred to as “monocores.” Monocore silencer design is mature in the modern silencer market and has existed for decades. Advantages of monolithic cores include simplified manufacturing, system alignment, and in the case of the DSX, generous expansion volumes for the 5.56x45mm cartridge, resulting in significant muzzle signature suppression.
Despite its large volume, the DSX is not a “low backpressure” silencer. Just as mature as monocore designs, is the antiquated (and incorrect) assertion that silencer backpressure is a function of internal volume. Silencer backpressure is a function of shock propagation and gross flow rate. The DSX possesses significant overall flow restriction, as evidenced in the measured waveforms, weapon kinematics, and ejection port signature contribution to shooter hazard on the standard MK18 weapon system. This phenomenon is further illustrated in the significantly improved performance of the DSX at the shooter’s ear when using the tuned SURG system in lieu of the standard 0.070” gas port MK18 upper assembly. The testing and analysis of the DSX with the SURG system is the subject of the next article in this series, published concurrently.
The DSX possesses some relatively unique features for a duty-use 5.56 silencer. For example, it is user serviceable; the steel monocore can be removed from the titanium tube for maintenance. There exists a steel retention spring that helps to prevent unintended system disassembly during use. If the user does not wish to field the silencer in the direct thread configuration, the DSX-M model exists in which the direct thread insert can be removed and the user’s choice of so-called “HUB” mounting systems can be installed.
The performance of the Maxim Defense DSX, for the size, is not necessarily an outlier in the overall state of practice. However, it is the first example of a monocore design published in The Silencer Sound Standard analysis pedigree, to date. The fact that it also happens to exhibit significant 5.56x45mm SBR suppression performance is also notable. Also notable is that the DSX is rated to pass multiple SOCOM SURGE firing cycles, on barrels as short as 5 inches.
In this review, the DSX performance metrics depend upon suppressing a supersonic centerfire rifle cartridge on a short barrel gas-operated rifle, which is an incredibly difficult task. PEW Science encourages the reader to remain vigilant with regard to all supersonic centerfire rifle suppression claims. The gas volume and combustion products created by the firing of the supersonic 5.56x45mm cartridge are significant; the measured pressure and impulse magnitudes, and their durations, illustrate this fact. Silencer performance on automatic (reciprocating) rifles depends on many factors. Weapon configuration may significantly influence total suppressed small arm system performance.
The hearing damage potential of supersonic centerfire rifle use is significant. PEW Science encourages the reader to consider the Suppression Rating when deciding on an appropriate silencer and host weapon combination for their desired use.
