SSS.6.82 - Energetic Armament ARX and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle
/Energetic Armament ARX on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The ARX is designed and manufactured by Energetic Armament. It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm NATO cartridge. It has a 1.5-inch diameter and is 5.8 inches in length with the included direct-thread mount. The ARX is a tubeless silencer, constructed primarily of fully-welded C300 maraging steel alloy, but possesses bi-metal baffles, in that the mouths of each axial baffle orifice are Stellite steel alloy for high temperature erosion control. The user may choose to install third-party mount adapters compatible with the 1.375”-24tpi system. The silencer weighs 8 ounces and the direct-thread mount weighs 0.8 ounces, for a total system weight of 8.8 ounces. The ARX can be obtained from Energetic Armament Dealers.
This Sound Signature Review contains single-test results using the Energetic Armament ARX with the direct-thread mount 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 6.82.1 contains the ARX test results and analysis.
Section 6.82.2 contains Suppression Rating comparisons of the ARX with dedicated 223 and 30 caliber silencers on the current market, including the KAC QDSS-NT4, Rugged Razor556, Otter Creek Labs Polonium, Surefire SOCOM556-RC2, HUXWRX HX-QD 556, Q Trash Panda, CGS Helios QD, SilencerCo Saker 556, Rugged Razor762, and others.
Section 6.82.3 contains the review summary and PEW Science subjective opinions.
Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the Energetic Armament ARX mounted with the direct-thread mount achieved a composite Suppression Rating™ of 21.5 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
6.82.1 Energetic Armament ARX Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the ARX 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. 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. Energetic Armament ARX Sound Metric Summary
6.82.1.1 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 ARX 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 all the shots.
Fig 1a. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The Energetic Armament ARX is a significantly over-bored silencer for the 5.56x45mm platform. Immediate similarities between the ARX pressure signatures (Fig 1b) and impulse signatures (Fig 2) and other silencers are apparent. These waveforms measured at the muzzle share similarities with those from other over-bored silencers such as the Rugged Razor762 (Review 6.58), the Rugged Razor556 (Review 6.76), the Q Trash Panda (Review 6.61), and the CGS Helios QD (Review 6.66).
However, unlike the aforementioned silencers, the Energetic Armament ARX generates significantly severe early time jetting; it is some of the most severe jetting overpressure measured on the suppressed MK18 weapon platform by PEW Science, to date. The peak FRP from the ARX reaches an overpressure of 155.8 dB, and in conjunction with the prolonged significant positive phase duration which continues for almost a full millisecond past bullet shock, it forms a severe muzzle signature. For context, the over-bored Rugged Razor762 generates a similarly severe signature to bystanders; this is reflected in their similar muzzle Suppression Ratings. The reader in encouraged to reference the PEW Science Rankings in Section 7 of the Silencer Sound Standard for further suppression performance context.
PEW Science Research Note 1: The Energetic Armament ARX exhibits a relatively high flow rate (relatively low back pressure), as evidenced by the significantly steep initial positive phase impulse rise in Figure 2a. This flow rate is due to its large over-bore. As discussed in SSS.6.58.1.1, a larger axial orifice results in different gas dynamics than the more complex internal geometry of silencers that achieve high flow rate through other methods (e.g. OSS / HUXWRX silencers with lengthened flow paths or Surefire silencers with baffle venting). Using only axial over-bore to achieve high flow rate has significant performance consequences.
Like many rifle silencers, the ARX relies on the trapping of gas to suppress sound signature. As its bore size increases relative to cartridge diameter, the suppression performance drops; this phenomenon is exacerbated by its baffle design and is further evident in the more erratic impulse waveforms (Figure 2). The Energetic Armament ARX is an inefficient short barrel 5.56x45mm silencer, in that its flow rate is measurably lower than that of the HUXWRX (OSS) HX-QD 556 (Review 6.54), HUXWRX (OSS) HX-QD 556k (Review 6.64), and KGM R556 (Review 6.60) but its sound suppression performance is also lower. The user may choose to install a 5.56 mm bore endcap in place of the standard 30 caliber endcap on the Energetic Armament ARX. The use of the 5.56 mm endcap is postulated to change the gas dynamics, and thus the suppression performance, of the ARX on this platform. This phenomenon was explored with the Rugged Razor762 in PEW Science Member Research Supplement 6.59.
PEW Science Research Note 2: The Energetic Armament ARX also exhibits significant variation in impulse accumulation rates. When examining the measured impulse waveforms in Figure 2a, the rate of positive phase pressure accumulation, which results in impulse rise, is reduced in later shots. Similar phenomena was measured in the testing of the Knights Armament QDSS-NT4 (Review 6.78), as well as in the testing of the Rugged Razor762, Q Trash Panda, and Helios QD on the MK18. Although similar, the behavior from the ARX is postulated to occur due to over-bore; the large axial orifice being unable to successfully suppress secondary combustion from the short 5.56x45mm barrel during all shots. This differs from the phenomenon in the KAC QDSS-NT4 tests in which interstitial baffle volume is postulated to have played a role.
The practical consequence of this variation in impulse accumulation rate, and thus prolonged positive phase impulse duration, is significant late-shot-string signature. Although the FRP to bystanders from the ARX is severe, later shots in the string may be even more severe. In this test, Shot 5 exhibited the highest hearing damage risk to bystanders (even more severe than the first shot).
PEW Science Research Note 3: 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 87 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 4: 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 5: Note that the muzzle Suppression Rating of the Energetic Armament ARX with the direct-thread mount is 16.6 and the at-ear Suppression Rating is 19.2; the same zone on the Suppression Rating Dose Chart. The higher axial flow rate of the ARX is detrimental to the sound signature at the shooter’s ear on the standard MK18 weapon system; the back pressure is low, but the muzzle signature is so severe that the weapon operator is still subjected to significant overpressure. As with the use of many silencers on the standard MK18, caution should be exercised by the weapon operator. The signatures measured at the shooter’s ear are presented below.
6.82.1.2 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 and Shot 2. The real sound impulse (momentum transfer potential) histories at the ear from the same 5-shot test are shown in Figure 4. Again, full and short timescales are shown.
Figure 3a. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature
Figure 3b. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Figure 4a. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature
Figure 4b. Energetic Armament ARX 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature Peaks
The FRP with the Energetic Armament ARX on the MK18, at the shooter’s ear, is significant. The inner-ear response severity of the first shot signature, to the shooter, was measured to be almost 56-percent more severe than the overall average, in accordance with PEW Science inner ear response modeling.
PEW Science Research Note 6: The detrimental effects of over-bore observed in the muzzle waveforms are again observed in waveforms measured at the shooter’s ear. In Figure 4, the contribution of the muzzle signature to the signature near the shooter’s head is plainly visible by the duplication of impulse plateaus later in the shot string. The same significant positive phase impulse rise, and variation from shot to shot, is displayed. Note the delayed impulse accumulation later in the shot string (Shot 4, Figure 4b). Secondary combustion from the short barrel MK18 weapon system, with an over-bored silencer like the ARX, results in continuous muzzle signature hazards that impact the shooter. The multi-peak nature of impulse accumulation in Shot 4 highlights this phenomenon; continuous pressure jetting is accumulating to produce impulse rise; the baffles are buffering the pressure propagation but the bore size is too large to effectively throttle the gas flow. This inefficiency continues through the shot string.
These phenomena are common consequences of over-bore silencer use on the MK18.
6.82.2 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 5 presents a comparison of the PEW Science Suppression Rating of the Energetic Armament ARX with the direct-thread mount 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 5. Suppression Rating Comparisons of the Energetic Armament ARX and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
The detrimental effect of the significant over-bore of the Energetic Armament ARX on the MK18 weapon system is apparent in the above data. The ARX exhibits significant flow rate (relatively low back pressure), but because it accomplishes this flow rate only through significant over-bore, exhibits a Suppression Rating at the muzzle that is on-par with that of the Rugged Razor762 (a 30 caliber rifle silencer). Like in the case of the Razor762, the severe muzzle signature of the ARX impacts the signature at the shooter’s ear, lowering it to levels below that of higher backpressure silencers like the Otter Creek Labs Polonium (6.75) and SilencerCo Saker 556 (Review 6.53). Whereas the Polonium and Saker exhibit severe at-ear signatures on the MK18 due to additive ejection port pressure to the holistic signature, the ARX exhibits severe at-ear signature due to severe muzzle signature. The Polonium and Saker signatures may be influenced by so-called weapon tuning. The signature of the Energetic Armament ARX may only be influenced by end cap (orifice) change to reduce severe blast overpressure.
As previously stated, the Energetic Armament ARX is an inefficient short barrel 5.56x45mm silencer, in that its flow rate is measurably lower than that of the HUXWRX (OSS) HX-QD 556 (Review 6.54), HUXWRX (OSS) HX-QD 556k (Review 6.64), and KGM R556 (Review 6.60) but its sound suppression performance is also lower. Again, the user may choose to install a 5.56 mm bore endcap in place of the standard 30 caliber endcap on the Energetic Armament ARX. The use of the 5.56 mm endcap is postulated to change the gas dynamics, and thus the suppression performance, of the ARX on this platform. PEW Science investigated this phenomenon with the Rugged Razor762 in PEW Science Member Research Supplement 6.59.
Interestingly, the Energetic Armament ARX achieves the same Suppression Rating at the shooter’s ear on this platform as the Rugged Razor556 (Review 6.76). However, the Razor556 is quieter to bystanders. The sound field difference from the two silencers is due, primarily, to a different flow rate balance on this weapon system.
The threshold of so-called “balanced performance” of 5.56 silencers with flow rate and muzzle suppression is relatively narrow, for conventional baffle designs. The test data presented in this article indicates that the Energetic Armament ARX has performance that is skewed toward flow rate, and not suppression. 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.
As discussed, more advanced design features than axial over-bore are required to increase flow rate (reduce back pressure) and still maintain high sound suppression performance. This performance-based design balance is a continued subject of PEW Science research.
6.82.3 Review Summary: Energetic Armament ARX 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 Energetic Armament ARX mounted with the direct-thread mount achieved a composite Suppression Rating™ of 21.5 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 Energetic Armament ARX is a relatively compact 5.56mm machine gun rated rifle silencer that possesses a high flow rate at the expense of sound signature suppression performance on the MK18. The silencer is extremely light, and weighs 8.8 ounces with its included direct-thread mount.
Like other centerfire rifle silencers from Energetic Armament, the ARX uses straight cone baffles in a welded tubeless configuration. The principle design factor driving the performance of the ARX silencer is the significant baffle orifice over-bore. Although this over-bore does increase flow rate (reduce back pressure) and also assist with system durability and erosion reduction when subjected to severe muzzle jetting on short barrel rifles, it also significantly influences sound signature performance. The muzzle signature of the ARX is so severe that the backpressure reducing effects (the reduction of so-called “port pop”) is of little consequence to the signature at the shooter's head. The behavior of the ARX on the MK18 weapon system is extremely similar to that of 30 caliber silencers like the Rugged Razor762.
The user may choose to install a 5.56 mm bore endcap in place of the standard 30 caliber endcap on the ARX. The use of the 5.56 mm endcap is postulated to change the gas dynamics, and thus the suppression performance, of the ARX on this platform. This phenomenon was explored with the Rugged Razor762 in PEW Science Member Research Supplement 6.59.
In addition to the large over-bore of the ARX baffles, other design features are present to further reduce erosion. The baffles are “bi-metal;” the primary material being C300 steel alloy and the mouths being Stellite. C300 steel is not capable of significant erosion resistance at high temperature; the more resilient (but less ductile) Stellite alloy allows for high temperature and abrasive particulate impact without significant erosion over the service life of the silencer. Stellite is also used in silencers from Rugged and Dead Air, albeit in complete baffle castings.
The erosion-reducing features (significant over-bore and Stellite baffle mouths) of the Energetic Armament ARX are intended to increase durability with severe firing schedules. PEW Science has not evaluated the durability of the ARX silencer on automatic weapon systems. The user is encouraged to contact the manufacturer for proper firing schedule and cartridge-use guidance.
The rear of the ARX is threaded for universal mount adaptation. The user may choose to install third-party adapters compatible with the 1.375”-24tpi system. This feature allows for significant adaptability of the silencer, should the included direct-thread adapter not be used.
In this review, the ARX 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.
