SSS.6.211 - Dillon Rifle Company DRC308 and the KAC SR-25 7.62x51mm 14.5-in Barrel Automatic AR-10 Rifle (Free Version)
/Dillon Rifle Company DRC308 on the KAC 7.62x51mm SR-25 with 14.5-in Barrel
The DRC308 is distributed by Dillon Rifle Company. It is a 30 caliber centerfire rifle silencer, intended to suppress the 7.62x51mm cartridge with semiautomatic or fully automatic fire. The DRC308 has a 1.75-inch diameter and is 6.5 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 tested third-party 3/4-24tpi direct-thread mount increased the system length to 6.84 inches. The included 5/8-24tpi direct-thread mount is similarly sized. 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 DRC308 structure is monolithic and constructed from 3D printed Inconel alloy. The silencer weighs 17.9 ounces and the tested direct thread mount weighs 1.2 ounces, for a total system weight of 19.1 ounces, as tested. The DRC308 can be obtained from Dillon Rifle Company.
Silencer Hazard Map:
The predicted personnel hazards generated by the tested weapon system in this report, in the free field, are shown in the adjacent Silencer Hazard Map. Click or tap the Map to enlarge. Please reference Silencer Hazard Map Brief 8.1.8 for further details. The PEW-SOFT HD Blast Hazard Prediction Tool and Hazard Mapper is presented in Report 8.1.1.
Dillon DRC308 14.5-in SR-25 AR-10 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data
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-136-001-25. Therefore, data pertaining to the DRC308 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 DRC308 on the KAC SR-25 Automatic AR-10 rifle, chambered in 7.62x51mm NATO with a 14.5-inch barrel. Lake City M80 149gr ammunition was used in the tests. The standard PEW Science KAC SR-25 test host weapon system is described in Public Research Supplement 6.210.
Section 6.211.1 contains Dillon DRC308 test results and analysis.
Section 6.211.2 contains overall gross Suppression Rating comparisons of the Dillon DRC308 and the unsuppressed KAC SR-25 automatic rifle.
Section 6.211.3 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 14.5-in barrel KAC SR-25 and fired with Lake City M80 149gr ammunition, the Dillon DRC308 achieved a composite Suppression Rating™ of 25.9 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.
6.211.1 Dillon DRC308 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the Dillon DRC308 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 DRC308 Sound Metric Summary
6.211.1.1 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 DRC308 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 DRC308 7.62x51mm NATO 14.5-in SR-25 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Dillon DRC308 7.62x51mm NATO 14.5-in SR-25 Automatic Rifle Sound Pressure Signature
Figure 2a. Dillon DRC308 7.62x51mm NATO 14.5-in SR-25 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Dillon DRC308 7.62x51mm NATO 14.5-in SR-25 Automatic Rifle Muzzle Sound Impulse Signature
Like the smaller DRC556, the Dillon DRC308 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 DRC308 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)
Dillon DRC556 - 5.56 M4A1 (6.194)
Of the above five silencers, the design of the Dillon DRC308 is most similar to that of the Dillon DRC556 in its DMLS (3D printed) Inconel alloy construction and gross envelope. However, it is important to note that the DRC308 is over an inch longer than the DRC556.
PEW Science Research Note 1: In addition to external geometry, there are some minor differences between the DRC308 and DRC556; there is some additional vent area on the first reflector (blast baffle) of the DRC308. Like the DRC556 and the PTR VENT Spiritus, multiple flow paths, including annular rerouting, are present in the DRC308. 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 DRC556 and Spiritus. However, initial conditions in the blast chambers of the Dillon silencers allow less blast load clearing in early time; there is less radial and annular venting around the blast baffle than in the PTR Spiritus and this directly induces elevated internal blast load impulse accumulation in early time. One result of this behavior on 5.56 platforms is extremely efficient gross suppression performance from the system, for its length. The use of PIP in the DRC556 provides almost the same gross muzzle suppression as the Spiritus, on average, in a shorter envelope. The DRC308, being longer to deal with more severe 7.62 NATO combustion, may still provide efficient performance for its length. Further research on the SR-25 platform is needed to quantify relative performance potentials (see Research Note 2).
PEW Science Research Note 2: Using the Suppression Rating Parametric Visualization Tool (Members Only), and limiting the maximum tested system length to 6.84 inches, filtering for .308 ammunition, 17 silencer configurations are shown to compare with the Dillon DRC308. With a muzzle Suppression Rating of 24.4, the DRC308 is in the top 10 performers in that metric, and the range of muzzle Suppression Ratings is 18.6 to 28.4, on the 20-in bolt-action rifle test host. Preliminarily, it is postulated that the DRC308 produces competitive signature suppression performance, for its size, in this combustion regime. It is extremely important to note that the blast overpressure input from a 20-in barrel 7.62 NATO system and 14.5-in barrel 7.62 NATO system are significantly different. Furthermore, it is also important to note that the Dillon DRC308 is intended for automatic (reciprocating) rifle use; not bolt-action rifle use. Therefore, its flow rate and blast load input bias are optimized for the host weapon type in this test program, not for longer barrel locked breach weapons.
PEW Science Research Note 3: The behavior of the Dillon DRC308 on the 14.5-in barrel 7.62x51mm NATO SR-25 is somewhat unique, in the context of comparison with 5.56 NATO combustion propagation behavior on similar barrel lengths, and also different from the behavior of 7.62 NATO signatures measured from 20-in barrels in the research. The DRC308 SR-25 signatures shown above possess the following attributes:
The DRC308 produces relatively high peak free field blast overpressure amplitude, but with a short blowdown duration (Fig. 1a).
The positive phase from initial jetting is longer duration than typically seen in 5.56 combustion (Fig. 1b).
First-round-pop (FRP) from the system exhibits divergence during initial coupled jetting and primary jetting, but relaxes during secondary jetting and into blowdown (Fig. 1b and Fig. 2).
Blast load impulse accumulation, post-primary jetting, is significantly reduced in amplitude (Fig. 2a).
Post-FRP consistency is robust, with accumulation rate consistency between FRP and post-FRP shots in the string (Fig. 2b).
The above observations are interesting when compared to a highly prolific 30 caliber rifle silencer fielded on the 20-in barrel bolt-action rifle - SilencerCo Omega 300 (6.10). The SilencerCo Omega 300 achieves a muzzle Suppression Rating of 24.8 on that weapon system; only nominally higher than the DRC308 muzzle Suppression Rating of 24.4. The Omega 300 produces significantly lower peak blast impulse 1.0 m left of the end cap of the silencer, however the blast overpressure blowdown duration from the silencer is significantly longer than from the DRC308; note the impulse histories transition into the negative phase later with the Omega. The behavior of the two silencers on the two different host weapons is significantly different, despite the relatively similar personnel risk metrics 1.0 m left of the end cap, in the free field.
PEW Science Research Note 4: FRP is significantly suppressed with the DRC308 and relative risk increase to bystanders during the FRP event may be considered negligible on this host weapon.
PEW Science Research Note 5: As in all semiautomatic rifle 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 98 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 automatic rifle bolts is often 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 DRC308 is 24.4 and the at-ear Suppression Rating is 18.8; the same zone on the Suppression Rating Dose Chart. In the tested configuration, the blast loads from the tested weapon system are significantly suppressed, but not suppressed enough for a human to forgo the use of hearing protection, for most use cases. Use of this silencer on the SR-25, when compared to firing the SR-25 unsuppressed, may significantly reduce the risk of blast overpressure injuries, such as traumatic brain injury (TBI), particularly near reflecting surfaces.
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 SR-25 weapon system are compared in the following section.
6.211.2 Suppression Rating Comparison (7.62x51mm from the 14.5-in SR-25)
Figure 5 presents a comparison of the PEW Science Suppression Ratings of the Dillon DRC308 with that of the unsuppressed KAC SR-25 weapon system. The standard PEW Science SR-25 test host weapon system is described in Public Research Supplement 6.210. As PEW Science research with the KAC SR-25 system continues, the dataset will be further populated.
Figure 5. Suppression Rating Comparisons of the Dillon DRC308 and the Unsuppressed 14.5-in KAC SR-25, 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 DRC308 on the 14.5-in KAC SR-25 weapon system with a direct-thread mount. Data is also presented for the fielding case of the unsuppressed KAC SR-25. 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.
As previously discussed in Research Note 3, the above observations are interesting when compared to a highly prolific 30 caliber rifle silencer fielded on the 20-in barrel bolt-action rifle - SilencerCo Omega 300 (6.10). The SilencerCo Omega 300 achieves a muzzle Suppression Rating of 24.8 on that weapon system; only nominally higher than the DRC308 muzzle Suppression Rating of 24.4. The Omega 300 produces significantly lower peak blast impulse 1.0 m left of the end cap of the silencer, however the blast overpressure blowdown duration from the silencer is significantly longer than from the DRC308; note the impulse histories transition into the negative phase later with the Omega. The behavior of the two silencers on the two different host weapons is significantly different, despite the relatively similar personnel risk metrics 1.0 m left of the end cap, in the free field.
As it stands, the Dillon DRC308 is less than 7 inches long, with its mount, and significantly reduces operator hazard when compared to the fielding of an unsuppressed 14.5-in barrel SR-25. Short barrel 7.62 NATO weapons are significantly hazardous to personnel. It is is important to note that blast overpressure may damage not only a human’s ears, but a human’s brain. Suppressed shooting is highly recommended.
PEW Science Research Note 11: 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 DRC308, in a 6.84-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 12: Several silencers possessing hybrid design traits are expected to exhibit performance differentials on the standard 20-in .308 bolt-action and 14.5-in SR-25 test host weapon systems. PEW Science urges extreme caution when attempting to extrapolate the 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 automatic rifle; all other things equal. For details on performance increases that are possible when “tuning” an automatic weapon system for a silencer, please see Review 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 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.
6.211.3 Review Summary: Dillon Rifle Company DRC308 on the KAC 7.62x51mm SR-25 with 14.5-in Barrel
When paired with the 14.5-in barrel KAC SR-25 and fired with Lake City M80 149gr ammunition, the Dillon DRC308 achieved a composite Suppression Rating™ of 25.9 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 DRC308 is a midsize 7.62mm rifle silencer with competitive muzzle suppression performance for its size, optimized for automatic (reciprocating) rifle use. Constructed entirely of 3D-printed Inconel alloy, the silencer also offers the requisite durability for heavy firing schedules. The DRC308 is HUB-mountable and produces gross free field muzzle blast suppression on supersonic rifle platforms on par with some longer silencers; with the tested direct-thread mount, the silencer is only 6.84-in long. This performance, for form factor, is postulated to be significant. The back pressure induced by the DRC308 is not significantly high.
Like the smaller DRC556, the Dillon DRC308 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 DRC308 design utilizes Purposely Induced Porosity (PIP) technology both internally and at venting locations. Of those silencers, the design of the Dillon DRC308 is most similar to that of the Dillon DRC556 in its DMLS (3D printed) Inconel alloy construction and gross envelope. However, it is important to note that the DRC308 is over an inch longer than the DRC556.
The DRC308, being longer to deal with more severe 7.62 NATO combustion, may still provide efficient performance for its length. Further research on the SR-25 platform is needed to quantify relative performance potentials. Using the Suppression Rating Parametric Visualization Tool available to PEW Science Members, and limiting the maximum tested system length to 6.84 inches, filtering for .308 ammunition, 17 silencer configurations are shown to compare with the Dillon DRC308. With a muzzle Suppression Rating of 24.4, the DRC308 is in the top 10 performers, and the range of muzzle Suppression Ratings is 18.6 to 28.4, on the 20-in bolt-action rifle test host. Preliminarily, it is postulated that the DRC308 produces competitive signature suppression performance, for its size, in this combustion regime.
It is interesting to compare the Dillon DRC308 to a highly prolific 30 caliber rifle silencer fielded on the 20-in barrel bolt-action rifle - the SilencerCo Omega 300. The SilencerCo Omega 300 achieves a muzzle Suppression Rating of 24.8 on that weapon system; only nominally higher than the DRC308 muzzle Suppression Rating of 24.4. The Omega 300 produces significantly lower peak blast impulse 1.0 m left of the end cap of the silencer, however the blast overpressure blowdown duration from the silencer is significantly longer than from the DRC308. The behavior of the two silencers on the two different host weapons is significantly different, despite the relatively similar personnel risk metrics 1.0 m left of the end cap, in the free field.
It is likely that the durability of the Dillon DRC308 is higher than many silencers on 7.62 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 DRC308 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 tested system was used with a third-party direct-thread mount as the KAC SR-25 is threaded 3/4-24tpi (different from the common 5/8-24tpi of many 30 caliber systems).
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 DRC308, in a 6.84-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 DRC5308 performance metrics depend upon suppressing a supersonic centerfire rifle cartridge on a short barrel gas-operated 7.62 NATO 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 7.62x51mm 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.
