SSS.6.139 - AAC M4-2000 Mod 08 and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle
/AAC M4-2000 Mod 08 on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The M4-2000 Mod 08 was designed and manufactured by Advanced Armament Corporation (AAC). It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm cartridge on barrels 10 inches and longer, with semiautomatic or fully automatic fire. The M4-2000 has a 1.5-inch diameter and is 6.6 inches long. The silencer is equipped with a built-in spring-ratchet latch system that interfaces with either 51-tooth AAC Blackout flash hider or AAC Brakeout muzzle brake mounts. Use of the flash hider increases the system length to 6.75 inches. The entirety of the M4-2000 baffle core is fully-welded Inconel 718 alloy with a stainless steel outer tube assembly. The silencer weighs 17.3 ounces and the Blackout flash hider mount weighs 3.9 ounces, for a total system weight of 21.2 ounces, as tested. The M4-2000 is no longer produced for the commercial market and is considered a legacy silencer.
Historical Note: The AAC M4-2000 Mod 08 is preceded in development, design, and distribution by other legacy silencer models, including the AAC M4-1000. The mounting system evolved from an 18-tooth system, to a 51-tooth system (tested here). Variations in the M4-2000 system have occurred, including:
Baffle stack changes; fewer baffles were used in initial iterations of the silencer design, as well as baffles of varying geometry. The AAC M4-2000 Mod 08 tested here has 7 fluted Inconel baffles.
Porting / vent configuration changes; the tested silencer contains no proximal vent array, nor any progressive baffle porting or venting, and is similar to the legacy AAC 556-SD rifle silencer internal design. Venting was implemented in the design after approximately production year 2013, similar to the design of the legacy AAC 416-SD rifle silencer.
The latch in the ratchet system may wear during use; later iterations of the silencer are equipped with different heat-treat and/or alloy latch material to improve service life.
Some of the above gross differences in iterations of the silencer’s design influence the sound signature to both bystanders and the shooter when using a semiautomatic rifle. Baffle quantity, shape, porting, and vent arrays all contribute to the holistic signature of the weapon system. This publication contains a performance evaluation of the unvented AAC M4-2000 Mod 08.
This Sound Signature Review contains single-test results using the M4-2000 Mod 08 mounted with the Blackout flash hider 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 6.139.1 contains the M4-2000 test results and analysis.
Section 6.139.2 contains Suppression Rating comparisons of the M4-2000 with dedicated 223 and 30 caliber silencers on the current market, including the PTR VENT 3, SilencerCo Velos LBP, BOSS Guillotine, CAT WB, PWS BDE 556, CAT ODB, Aero Precision Lahar-30L, Lahar-30, HUXWRX FLOW 762 Ti, Maxim Defense DSX, 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 6.139.3 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the AAC M4-2000 Mod 08 mounted with the Blackout flash hider mount achieved a composite Suppression Rating™ of 35.0 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
6.139.1 AAC M4-2000 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the M4-2000 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. AAC M4-2000 Mod 08 Sound Metric Summary
6.139.1.1 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 public dataset and bolt-closing signatures. The waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science laboratory sound signature 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 laboratory testing; the recognized 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 M4-2000 Mod 08 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. M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The AAC M4-2000 is an extremely high performance legacy 5.56 rifle silencer. It also exhibits significant flow restriction, or back pressure. Characteristic low amplitude normalized jetting is displayed in pressure space in Figure 1b, with relatively slow external gas momentum accumulation rates shown in Figure 2a. The long duration impulse plateau is typical of some high back pressure rifle silencer designs and is longer than that generated by even the KAC QDSS-NT4 (6.78), YHM Turbo T2 (6.98), BOSS Guillotine (6.133), and the SilencerCo Saker 556 (6.53); all examples of dedicated-bore 5.56mm rifle silencers with conventional baffles (the legacy KAC silencer notwithstanding).
PEW Science Research Note 1: The FRP signature of the tested M4-2000 is somewhat unique in that it is masked to bystanders. The gas momentum accumulation during the first shot is accelerated, as typically exhibited by a rifle silencer. However, upon reaching maximum accumulation, the FRP jetting decays and begins to enter rarefaction much earlier than typical. This FRP “quenching” in early time is highlighted in Figure 2b and results in no relative signature severity differential to bystanders during the first shot. This type of behavior is relatively atypical for a 5.56x45mm rifle silencer. In Shot 6, the silencer does exhibit erratic combustion propagation in early time. However, the jetting normalizes relatively quickly (Figure 2a).
PEW Science Research Note 2: The baffle stack of the M4-2000 (and this version of the Mod 08 iteration tested, specifically) contains seven fluted Inconel alloy cone baffles that are not ported. The proximal blast chamber geometry of the silencer is also unvented. These construction characteristics are notable, as several iterations of the M4-2000 design have proliferated though the market over the past decade. It is likely that blast chamber venting and baffle porting change gas propagation characteristics through the silencer in both early and late time, therefore changing the gross flow rate of the system and potentially influencing both weapon function and holistic sound signature differently. For this reason, the reader is cautioned that the performance characterized in this report is only valid for the unvented iteration of the AAC M4-2000 Mod 08.
The AAC M4-2000 Mod 08 exhibits higher back pressure than many silencers evaluated by PEW Science on the standard MK18 weapon system, to date. This behavior is most likely exacerbated in the tested non-ported/unvented design iteration.
PEW Science Research Note 3: Despite the legacy design of the M4-2000 system, its gross suppression performance is extremely competitive. For example, the tested M4-2000 Mod 08 exhibits slightly higher muzzle suppression performance than the modern CAT WB (6.129). The AAC silencer is larger, and produces significantly higher back pressure and operator hazard than the CAT silencer, but the gross comparison is still valid. The Surefire SOCOM556-RC2 (6.52) offers somewhat higher suppression performance than the tested iteration of the AAC M4-2000 Mod 08, all-around. While it is possible that the vented iteration of the M4-2000 may be closer to that of the Surefire silencer, further testing is needed to quantify that behavior.
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 72 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 and the alpha parameter. 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. There are other signature features measured at the shooter’s ear which may further assist with quantifying weapon kinematics.
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 AAC M4-2000 Mod 08 is 34.7 and the at-ear Suppression Rating is 20.5; different zones on the Suppression Rating Dose Chart. The lower flow rate (higher back pressure) of the M4-2000 contributes to a more severe ejection port signature, increasing the overall severity of the signature to the shooter on the standard MK18 weapon system. This phenomenon also occurs with other high back pressure silencers on the MK18 Caution should be exercised by the weapon operator. The signatures measured at the shooter’s ear are presented below.
6.139.1.2 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. An annotated timescale is displayed in Figure 3b, for Shots 1, 3, 4, and 5. 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. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature
Figure 3b. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Figure 4a. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature
Figure 4b. AAC M4-2000 Mod 08 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature Peaks
Like at the muzzle, the FRP severity differential to the shooter is nominal; the M4-2000 does not exhibit FRP that is more hazardous than subsequent shots, to bystanders or to the weapon system operator. However, the tested M4-2000 does possess significant back pressure that manifests directly in the following ways:
Ejection port blast is significant. Blast overpressure originating from the MK18 ejection port due to system pressure being higher than typical at the time of unlock is shown in Figure 3b. The gas velocity gradients induce subsequent negative pressure phase (rarefaction) which is observed to increase as the shot string continues. These phenomena are due to the elevated temperature of the system further restricting free gas expansion; the combustion gasses are unable to cool as significantly throughout the shot string.
Gas momentum transfer potential (blast load impulse) at the operator’s head is significant. This is presented in Figure 4. Note again that the trend increases in subsequent shots as system heating occurs.
Gas toxicity, uncharacterized directly by the evaluation, is postulated to increase significantly in this configuration, particularly with rapid fire.
These at-ear signature features are extreme and indicate the presence of significant gas flow momentum near the shooter’s head.
PEW Science Research Note 7: Weapon tuning for use of the AAC M4-2000 Mod 08 may be preferred or required by system operators desiring to optimize system performance and reduce hazard. For details on performance increases that are possible when “tuning” an AR-15 weapon system for a silencer, please see Review 6.111. As the M4-2000 exhibits a high degree of muzzle suppression, weapon system tuning may pay dividends for gross signature hazard reduction to the operator, in general.
It is important to note that not all silencers will possess a significant 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. Specific weapon system parameters will dictate modification efficacy.
6.139.2 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 6 presents a comparison of the PEW Science Suppression Rating of the AAC M4-2000 Mod 08 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 AAC M4-2000 Mod 08 and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 6 presents 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 during the entire time regime of weapon operation, including combustion, complete blowdown, and all mechanical operation, including the carrier group returning to battery, in the true free field. The parameter may be used with the dose chart at the beginning of this report.
It is very important to note that performance differentials outside the free field (e.g. near reflecting surfaces) may not scale linearly across all designs. This is due to blast load reflection factors varying with both amplitude and wave shape, along with other waveform components.
From the above data, it can be concluded that the legacy AAC M4-2000 Mod 08 design exhibits extremely competitive performance with many modern rifle silencers on the standard untuned MK18 weapon system. Its muzzle suppression performance is relatively high. Note, however, the relatively low Suppression Rating at the shooter’s ear. This is a direct consequence of the silencer’s extreme back pressure which results in more hazardous ejection port blast loading coalescing with suppressed muzzle blast.
The tested M4-2000 Mod 08 exhibits slightly higher muzzle suppression performance than the modern CAT WB (6.129). The AAC silencer is larger, and produces significantly higher back pressure and operator hazard than the CAT silencer, but the gross comparison is still valid. The Surefire SOCOM556-RC2 (6.52) offers higher suppression performance than the tested iteration of the AAC M4-2000 Mod 08, all-around. While it is possible that the vented iteration of the M4-2000 may be closer to that of the Surefire silencer, further testing is needed to quantify that behavior.
PEW Science Research Note 8: On this weapon system, the tested AAC M4-2000 Mod 08 induces operator hazard on par with that of the Otter Creek Labs Polonium (6.75) and Polonium K (6.95), the Dead Air Sandman-S (6.92), Thunder Beast Dominus (6.105), and vented end-cap Helios QD (6.66). The similarity in operator hazard from the M4-2000 Mod 08 all of these silencers on the standard MK18 occurs for different reasons. In the case of the Polonium, it is due to similar back pressure exacerbating ejection port blast severity. In the case of silencers like the Sandman-S, Dominus, and vented end-cap Helios QD, the similar operator hazard is due to those silencers producing muzzle blast that is so severe that the operator level of protection drops further, regardless of ejection port blast.
PEW Science Research Note 9: Due to the breadth of the Silencer Sound Standard testing and analysis pedigree, the reader is encouraged to examine the spectrum over which suppression performance on the MK18 has been demonstrated. There exist silencers evaluated on the 5.56x45mm short barrel rifle platform that have significantly lower performance. Because the PEW Science Suppression Rating is a damage risk criterion (DRC), a lower Suppression Rating indicates a higher personnel hazard in the free field. Therefore, such silencers are postulated to be more hazardous to the unprotected ear than silencers like the AAC M4-2000 Mod 08. To iterate, the Suppression Rating is a DRC - it is not a subjective quantity; it is an objective quantification of hearing damage risk potential.
Weapon tuning for use of the AAC M4-2000 Mod 08 may be preferred or required by system operators desiring to optimize system performance and reduce hazard. It is important to note that not all silencers will possess a significant 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. Specific weapon system parameters will dictate modification efficacy.
6.139.3 Review Summary: AAC M4-2000 Mod 08 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 AAC M4-2000 Mod 08 mounted with the Blackout flash hider mount achieved a composite Suppression Rating™ of 35.0 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 legacy AAC M4-2000 Mod 08 is a full size 5.56mm machine gun rated rifle silencer that exhibits high sound suppression performance and is competitive with modern designs. The silencer exhibits a high degree of durability, as well as high back pressure. It is important to note that there have been several design iterations of M4-2000 rifle silencers through the history of the original Advanced Armament Corporation.
The AAC M4-2000 Mod 08 is preceded in development, design, and distribution by other legacy silencer models, including the AAC M4-1000. The mounting system evolved from an 18-tooth system, to a 51-tooth system (tested here). Variations in the M4-2000 system have occurred, including baffle stack changes; fewer baffles were used in initial iterations of the silencer design, as well as baffles of varying geometry. The AAC M4-2000 Mod 08 tested here has 7 fluted Inconel baffles. Variations have also occurred with porting and vent configuration changes; the tested silencer contains no proximal vent array, nor any progressive baffle porting or venting, and is similar to the legacy AAC 556-SD rifle silencer internal design. Venting was implemented in the design after approximately production year 2013, similar to the design of the legacy AAC 416-SD rifle silencer.
Some of the above gross differences in iterations of the silencer’s design influence the sound signature to both bystanders and the shooter when using a semiautomatic rifle. Baffle quantity, shape, porting, and vent arrays all contribute to the holistic signature of the weapon system. This publication contains a performance evaluation of the unvented AAC M4-2000 Mod 08, which exhibits higher back pressure than many silencers evaluated by PEW Science on the standard MK18 weapon system, to date. This behavior is most likely exacerbated in the tested non-ported/unvented design iteration.
Despite the legacy design of the M4-2000 system, its gross suppression performance is extremely competitive. For example, the tested M4-2000 Mod 08 exhibits slightly higher muzzle suppression performance than the modern CAT WB. The AAC silencer is larger, and produces significantly higher back pressure and operator hazard than the CAT silencer, but the gross comparison is still valid. The Surefire SOCOM556-RC2 offers somewhat higher suppression performance than the tested iteration of the AAC M4-2000 Mod 08, all-around. While it is possible that the vented iteration of the M4-2000 may be closer to that of the Surefire silencer, further testing is needed to quantify that behavior.
On this weapon system, the tested AAC M4-2000 induces operator hazard on par with that of the Otter Creek Labs Polonium and Polonium K, the Dead Air Sandman-S, Thunder Beast Dominus, and vented end-cap Helios QD. The similarity in operator hazard from the M4-2000 Mod 08 all of these silencers on the standard MK18 occurs for different reasons. In the case of the Polonium, it is due to similar back pressure exacerbating ejection port blast severity. In the case of silencers like the Sandman-S, Dominus, and vented end-cap Helios QD, the similar operator hazard is due to those silencers producing muzzle blast that is so severe that the operator level of protection drops further, regardless of ejection port blast.
The ratcheting latch system employed by the silencer is relatively simple to operate with 51-tooth AAC Blackout flash hider or Brakeout muzzle brake mounts. The latch in the ratchet system may wear during use; later iterations of the silencer are equipped with different heat-treat and/or alloy latch material to improve service life. Operationally, users may pre-compress the latch such that it does not interface with the mount teeth during installation until the final position. This practice may prolong latch serviceability.
The fully-welded Inconel alloy baffle stack of the AAC M4-2000 Mod 08 has a history of durability on 5.56x45mm automatic weapons. Blast baffle longevity on short barrels may be increased through the use of the brake mount rather than the 3-prong flash hider mount.
In this review, the AAC M4-2000 Mod 08 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.
