SSS.6.194 - Dillon Rifle Company DRC556 and the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle (Free Version)
/Dillon Rifle Company DRC556 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
The DRC556 is distributed by Dillon Rifle Company. It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm cartridge with semiautomatic or fully automatic fire. The DRC556 has a 1.75-inch diameter and is 5.38 inches long with no mount. The silencer may be attached to a variety of weapon systems depending on the user’s choice of mount; the included 1/2-28tpi direct thread mount increases the system length to 5.75 inches. Other mounting options are possible due to the rear of the silencer body being HUB compatible (1.375-24 tpi threading). The entirety of the DR556 structure is monolithic and constructed from 3D printed Inconel alloy. The silencer weighs 15.4 ounces and the included direct thread mount weighs 2.1 ounces, for a total system weight of 17.5 ounces, as tested. The DRC556 can be obtained from Dillon Rifle Company.
PEW Science is an independent private testing laboratory and also hosts the world’s only independent public 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 analysis production for this Sound Signature Review was funded in part by PEW Science Project PEW-Dillon-110-001-25. Therefore, data pertaining to the DRC556 in this Sound Signature Review is published with the express written permission of Dillon Rifle Company, Inc.
The testing and analysis presented in this Sound Signature Review are of the Dillon DRC556 on the M4A1 Mid-Gas Automatic AR-15 rifle, chambered in 5.56x45mm NATO with a 14.5-inch barrel. Federal XM193 55gr ammunition was used in the tests. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127.
Section 6.194.1 contains Dillon DRC556 test results and analysis.
Section 6.194.2 contains overall gross Suppression Rating comparisons of the Dillon DRC556 with other rifle silencers on the current market on the M4A1 Mid-Gas Rifle, including various configurations of the CAT TSWIF, Sylvan Arms SA223TIS, BOE Mod 1, Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, CAT/WB/A1, and Surefire SOCOM556-RC2.
Section 6.194.3 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the Dillon DRC556 achieved a composite Suppression Rating™ of 43.7 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.
6.194.1 Dillon DRC556 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the Dillon DRC556 direct-thread mounted is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. The data acquired 0.15 m (6 in) right of the shooter’s ear is only available to membership supporters of PEW Science and the Silencer Sound Standard. You can support public PEW Science testing, research, and development with a membership, here. State-of-the-art public firearm sound signature testing and research conducted by PEW Science is supported by readers like you.
Table 1. Dillon DRC556 Sound Metric Summary
6.194.1.1 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 Dillon DRC556 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. Dillon DRC556 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Dillon DRC556 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature
Figure 2a. Dillon DRC556 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Dillon DRC556 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
The Dillon DRC556 is a hybrid design, incorporating both high flow rate features and conventional geometries to control distal blast propagation while reducing adverse influence on weapon function. Specifically, it is classified as a staged hybrid in the PEW Science Silencer Sound Standard research taxonomy. For an overview of the three primary classes of rifle silencer designs, the reader is encouraged to review PEW Science Research Supplement 6.169. The DRC556 design utilizes Purposely Induced Porosity (PIP) technology both internally and at venting locations. Other silencers utilizing PIP technology evaluated by PEW Science in the public research pedigree include the:
PTR VENT 2 - 9x19mm MP5 (6.131)
PTR VENT 3 - 5.56x45mm MK18 (6.135)
PTR VENT 1 - 7.62x51mm bolt-action (6.160)
PTR VENT Spiritus 556i - 5.56 MK18 (6.175) and 5.56 M4A1 (6.176).
Of the above four silencers, the design of the Dillon DRC556 is most similar to that of the PTR VENT Spiritus 556i in its DMLS (3D printed) Inconel alloy construction and gross envelope. However, it is important to note that the DR556 is over half an inch shorter than the Spiritus, and larger in diameter.
PEW Science Research Note 1: In addition to external geometry, there are other differences between the DRC556 and Spiritus 556i; one of the most significant is the internal geometry of the first expansion chamber (blast chamber) and first reflector (blast baffle). Like the Spiritus, multiple flow paths, including annular rerouting, are present in the DR556. As a staged design, the silencer does allow for high pressure blast load to propagate through multiple areas of the silencer simultaneously, and a significant flow path terminates at distal and radial PIP vents; the external venting configuration is similar to that of the Spiritus. However, initial conditions in the blast chamber allow less blast load clearing in early time; there is less radial and annular venting around the blast baffle and this directly induces elevated internal blast load impulse accumulation in early time. One result of this behavior is extremely efficient gross suppression performance from the system, for its length. The use of PIP in the DRC556 has been implemented to provide almost the same gross muzzle suppression as the Spiritus, on average, in a shorter envelope.
PEW Science Research Note 2: Despite the similar gross muzzle suppression metrics, the behavior of the DRC556 and Spiritus on this host weapon platform are different:
The DRC556 produces lower peak free field blast pressure amplitude, but with longer blowdown duration (Fig. 1a).
First-round-pop (FRP) divergence is elevated in early time compared to that of the Spiritus (Fig. 1b), though maximum momentum normalization occurs at a lower amplitude (Fig. 2a).
Initial jet velocity is elevated which induces early rarefaction events (Fig. 1b).
External blast load impulse accumulation has clear staged propagation (Fig. 2a).
The longer blowdown in (1), lower momentum amplitude in (2), and staged propagation in (4) are all most likely significantly influenced by the differences in blast chamber. Early time blast load reflections do not clear expediently enough when compared to the Spiritus in the time regime of interest on this specific barrel length. The practical result of this behavior, on the standard 14.5-in M4A1RIII untuned mid-length gas AR-15 is higher back pressure than the Spiritus with almost identical gross suppression performance. This tradeoff illustrates one of the parametric performance traits of PIP technology. In this particular case, to achieve extreme levels of gross suppression performance in a shorter length envelope, some flow parameters were reduced, even with volumetric increases from diameter change. Nonetheless, the gross suppression performance of the Dillon DRC556 is very high, especially for its size. This is extremely notable given its 5.75-in total tested system length. Suppression performance of this level is highly unusual from a silencer of this size.
PEW Science Research Note 3: Despite almost uniform momentum amplitude at maximum accumulation throughout the shot string (Fig. 2a), the FRP that presents to bystanders in the free field from the Dillon DR556 is approximately 70 percent more severe than follow up shots on this barrel length, on average. It is postulated that due to the length of the system and the available PIP utilization, the ancillary combustion during the FRP event is not quenched as expediently as in the Spiritus, for example. There may potentially be a pressure stage delay due to the clearing differences discussed in Research Note 1. This hypothesis is supported by the presence of the initial accumulation peak in the impulse histories as described in (4) of Research Note 2. It is likely that the PTR Spiritus enables more expedient propagation of secondary combustion to internal PIP components and possesses enough length to enable a longer duration of contact with PIP before final distal vent, when compared to the Dillon silencer.
PEW Science Research Note 4: When comparing silencers of similar length(s) to the Dillon DRC556, the only silencer that comes close to meeting its gross suppression performance on this weapon system, published to date, is the CAT WB (6.130) which is approximately a third of an inch longer in its tested configuration. The muzzle (bystander) suppression performance of the WB is somewhat lower than that of the DRC556 on average, though the relative FRP suppression performance of the WB is superior. With regard to shooter (operator) suppression performance, the personnel risk reduction afforded by the CAT WB is more robust. This is due in large part to the much higher early time flow rate in the CAT WB. The CAT WB has lower back pressure in both early and late time than the Dillon silencer, in the tested configurations.
When compared to other short silencers tested and analyzed in the pedigree, the DRC556 offers significantly higher performance. The gross suppression of the silencer, as previously stated, is highly unusual for its size and is nontrivial. As an extreme point of comparison, note that the highest muzzle Suppression Rating in the public research pedigree as of the date of this report publication is produced by the 7.7-inch BOE Mod 1 on this same weapon system (6.183). The gross bystander risk reduction from the Dillon DRC556 is only nominally lower, and it is almost a full two inches shorter.
PEW Science Research Note 5: As in all semiautomatic AR-15 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 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 6: The closing time of the AR-15 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.
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 7: Note that the muzzle Suppression Rating of the DRC556 is 43.6 and the at-ear Suppression Rating is 21.0; different zones on the Suppression Rating Dose Chart. In the tested configuration, the back pressure of the Dillon DRC556 contributes to elevated operator hazard from ejection port blast on this weapon system. However, the total pressure field suppression performance of this compact system is very high and produces bystander personnel protection levels of large silencers on the standard M4A1 weapon system.
The signatures measured and analyzed at the shooter’s ear are presented in the full Member Version of this report.
Gross hazards and behaviors with the M4A1 weapon system are compared in the following section.
6.194.2 Suppression Rating Comparison (5.56x45mm from the M4A1)
Figure 5 presents a comparison of the PEW Science Suppression Ratings of the Dillon DRC556 with that of other rifle silencers on the M4A1 weapon system. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127. As PEW Science research with the M4A1 system continues, the dataset will be further populated.
Figure 5. Suppression Rating Comparisons of the Dillon DRC556 and the CAT TSWIF, Sylvan Arms SA223TIS, BOE Mod 1, Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, Surefire SOCOM556-MIN2, CAT WB, and SOCOM556-RC2 with different mounts, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 5 presents an overall summary of the postulated hazards to the operator and bystanders when fielding a Dillon DRC556 on the M4A1 weapon system with the included direct thread mount. Data is also presented for the fielding case of the CAT TSWIF (6.193), Sylvan Arms SA223TIS (6.187), BOE Mod 1 (6.183), Echo Zulu Defense X1R556-Ti (6.181), PTR VENT Spiritus 556i (6.176), HUXWRX FLOW 556 Ti (6.168), Surefire SOCOM556-RC2 (6.128), SOCOM556-MINI2 (6.144), and KAC QDC PRT units (6.156) on different muzzle devices, along with fielding of the CAT WB (6.130). Hazards are expressed with the Suppression Rating; a holistic parameter that captures human inner ear damage risk potential from a measured impulsive complex 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. The PEW Science Suppression Rating is a damage risk criterion (DRC), a lower Suppression Rating indicates a higher personnel hazard in the free field - it is not a subjective quantity; it is an objective quantification of hearing damage risk potential. Due to its true free field test data origin and complete waveform analytical calculation basis, it is the only known universal suppressed weapon system signature comparison metric available.
The following gross conclusions can be made from the above:
The Dillon DRC556 achieves hazard reduction to bystanders directly adjacent to the weapon system, in the free field, on the standard untuned M4A1RIII weapon system that is comparable to much longer silencers, including the PTR VENT Spiritus 556i and BOE Mod 1 with its solid end cap. Its gross free field suppression performance eclipses that of the CAT WB and FLOW 556 Ti on this weapon system, which is extremely notable. The performance gap between it and the 3-Prong-equipped Surefire SOCOM556-RC2 is extreme. At 5.75-in of total length as tested, the DRC556 is currently unmatched in gross muzzle Suppression Rating for the length, on this weapon system.
As a result of increased back pressure when compared to some silencers, the free field operator (shooter) hazard reduction with the Dillon DRC556 on the standard untuned M4A1RIII weapon system is on par with that of the high performance Echo Zulu Defense X1R556-Ti, which also exhibits somewhat of a lower early time flow rate and high muzzle suppression performance. In the free field, operator protection from the Dillon DRC556 will be similar to that of a 3-prong-equipped Surefire SOCOM556-MINI2 on this weapon system. That level of free field operator protection is also similar to that of a WARCOMP-equipped 556-RC2 or a 3-Prong-equipped KAC QDC/MCQ-PRT on this weapon system.
In this combustion regime on the standard untuned 14.5-in mid-length gas M4A1RIII AR-15, there are silencers in the research pedigree that do not reach the absolute muzzle suppression performance as the Dillon DRC556, but provide equivalent or higher operator protection in the free field. These silencers include the CAT TSWIF which is shorter than the DRC556 and the CAT WB, the holistic performance of which is very competitive. The KAC QDC/CRS-PRT also reduces hazard to the shooter in the free field, albeit at the expense of more hazardous conditions to a bystander adjacent to the weapon system. It is important to note that the HUXWRX FLOW 556 Ti significantly reduces hazard to the weapon operator in the free field.
It is important to note that the M4A1RIII is also a somewhat “over-gassed” rifle. Significant hazard reduction efficacy is extremely difficult to achieve without weapon modification. Furthermore, as discussed with in-depth analysis in previous Member Research Supplement 6.169 on the MK18, specific signature attributes and environmental factors can and will influence user perception and experience. Tuning of the M4 system for ejection port blast reduction may result in higher levels of overall operator hazard reduction performance with several silencers. FRP, however, will still influence operator hazard differentials during the first shot. That performance detriment can not be “tuned out” of the system without the use of some type of ablative medium.
Increased gross flow rate (lower back pressure) does pay dividends in ejection port blast hazard reduction to the 14.5-in barrel M4A1 midlength gas weapon operator, but without weapon modification, shooter’s ear protection levels may plateau. This has now been demonstrated several times with high performance silencers. Management of internal blast load impulse accumulation and flow rate in multiple time regimes is paramount for holistically balanced suppression performance on such weapon systems.
PEW Science Research Note 12: The use of PIP technology in silencers continues to present high performance cases. Perhaps just as significant are the performance potentials presenting in ever shrinking size envelopes. The gross free field muzzle blast suppression from the Dillon DRC556, in a 5.75-in total tested system length with mount, is expected to significantly influence expectations regarding the performance of compact supersonic rifle silencers. Performance potentials with reduced form factor are expected to be competitive as the implementations of technologies like PIP, and others, continue to advance.
PEW Science Research Note 13: Several silencers possessing hybrid design traits exhibit performance differentials on the standard 10.3-in MK18 and 14.5-in M4A1RIII test host weapon systems. PEW Science urges extreme caution when attempting to extrapolate performance of a silencer on either of these weapon systems to the other without instrumented test data and engineering analysis. Performance differentials may be counterintuitive due to the complexities of hybrid systems’ response to varying blast load input pressure(s) and duration(s).
As detailed in this report, the Suppression Rating at the shooter’s ear may be significantly influenced by the ejection port signature from an AR-15; all other things equal. For details on performance increases that are possible when “tuning” an AR-15 weapon system for a silencer, please see Report 6.111. 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.
Small arm weapon system suppression performance is a spectrum. The PEW Science Suppression Rating and the Silencer Sound Standard help quantify this spectrum for end users and industry, objectively.
6.194.3 Review Summary: Dillon Rifle Company DRC556 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the Dillon DRC556 achieved a composite Suppression Rating™ of 43.7 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 Dillon DRC556 is a somewhat compact dedicated 5.56mm rifle silencer with extreme muzzle suppression performance for its size. Constructed entirely of 3D-printed Inconel alloy, the silencer also offers the requisite durability for heavy firing schedules. The DRC556 is HUB-mountable and produces gross free field muzzle blast suppression on supersonic rifle platforms on par with that of much larger silencers; with its included direct thread mount, the silencer is only 5.75-in long. This performance, for form factor, is extremely significant. The back pressure induced by the DRC556 is not significantly high, though it is somewhat higher than some competing models in this performance class.
The Dillon DRC556 is a hybrid design, incorporating both high flow rate features and conventional geometries to control distal blast propagation while reducing adverse influence on weapon function. Specifically, it is classified as a staged hybrid in the PEW Science Silencer Sound Standard research taxonomy. The DRC556 design utilizes Purposely Induced Porosity (PIP) technology both internally and at venting locations similarly to the VENT series from PTR. Of those silencers, the design of the Dillon DRC556 is most similar to that of the PTR VENT Spiritus 556i in its DMLS (3D printed) Inconel alloy construction and gross envelope. However, it is important to note that the DR556 is over half an inch shorter than the Spiritus, and larger in diameter.
Other than external geometry, there are other differences between the DRC556 and Spiritus 556i; one of the most significant is the blast chamber and blast baffle. One result of these differences is extremely efficient gross suppression performance from the system, for its length. The use of PIP in the DRC556 has been implemented to provide almost the same gross muzzle suppression as the Spiritus, on average, in a shorter envelope. Another result is higher back pressure than the Spiritus with almost identical gross suppression performance. This tradeoff illustrates one of the parametric performance traits of PIP technology. In this particular case, to achieve extreme levels of gross suppression performance in a short length envelope, some flow parameters were reduced, even with volumetric increases from diameter change. Nonetheless, the gross suppression performance of the Dillon DRC556 is very high, especially for its size. This is extremely notable given its 5.75-in total tested system length. Suppression performance of this level is highly unusual from a silencer of this size.
In this combustion regime on the standard untuned 14.5-in mid-length gas M4A1RIII AR-15, there are silencers in the research pedigree that do not reach the absolute muzzle suppression performance as the Dillon DRC556, but provide equivalent or higher operator protection in the free field. These silencers include the CAT TSWIF which is shorter than the DRC556 and the CAT WB, the holistic performance of which is very competitive. The KAC QDC/CRS-PRT also reduces hazard to the shooter in the free field, albeit at the expense of more hazardous conditions to a bystander adjacent to the weapon system. It is important to note that the HUXWRX FLOW 556 Ti significantly reduces hazard to the weapon operator in the free field.
It is likely that the durability of the Dillon DRC556 is higher than many silencers on 5.56 NATO weapons. Due to its Inconel construction, the system is more resistant to particle erosion from high temperature and pressure jet impingement. Dillon recommends that fully automatic fire be conducted with 90 to 120 rounds fired in bursts, after which a 10-minute cool down period to ambient temperature should be allowed. The end user is encouraged to contact Dillon for further guidance.
The Dillon DRC556 is HUB mount capable, and includes a direct-thread mount. The user may adapt the silencer to a variety of mounting systems of their preference.
The use of PIP technology in silencers continues to present high performance cases. Perhaps just as significant are the performance potentials presenting in ever shrinking size envelopes. The gross free field muzzle blast suppression from the Dillon DRC556, in a 5.75-in total tested system length with mount, is expected to significantly influence expectations regarding the performance of compact supersonic rifle silencers. Performance potentials with reduced form factor are expected to be competitive as the implementations of technologies like PIP, and others, continue to advance.
In this review, the Dillon DRC556 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.
