SSS.6.104 - KAC 5.56 QDC and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)
/KAC 5.56 QDC on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The 5.56 QDC is manufactured by Knight’s Armament Company. It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm NATO cartridge. It has a 1.43-inch diameter and is 6.4 inches in length. Like its predecessor, the QDSS-NT4, the 5.56 QDC possesses a “crimped cone” baffle core constructed from Inconel steel alloy, which is welded to the primary tube. The silencer possesses an integral mounting collar with ball bearings that interface with sockets machined into KAC QDC muzzle devices. The silencer weighs 17.5 ounces and the 3-Prong flash hider weighs 2.4 ounces, for a total system weight of 19.9 ounces, as tested. The 5.56 QDC may now be considered a legacy silencer. Inquiries for acquisition should be directed to Knight’s Armament Company as inventory may not be available at vendors such as Silencer Shop.
This Sound Signature Review contains single-test results using the KAC 5.56 QDC with the 3-Prong 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 6.104.1 contains the 5.56 QDC test results and analysis.
Section 6.104.2 contains Suppression Rating comparisons of the 5.56 QDC with dedicated 223 and 30 caliber silencers on the current market, including the 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 6.104.3 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 KAC 5.56 QDC mounted with the 3-Prong flash hider mount achieved a composite Suppression Rating™ of 28.0 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
6.104.1 KAC 5.56 QDC Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the 5.56 QDC tested with the 3-Prong flash hider 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. The data acquired 0.15 m (6 in) right of the shooter’s ear is only available to membership supporters of PEW Science and the Silencer Sound Standard. You can support PEW Science testing, research, and development with a membership, here. State-of-the-art firearm sound signature testing and research conducted by PEW Science is supported by readers like you.
Table 1. KAC 5.56 QDC Sound Metric Summary
6.104.1.1 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 5.56 QDC are shown in Figure 1a. The sound signatures of Shot 1, Shot 2, and Shot 3 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 Shot 1 to that of Shot 2 and Shot 3.
Fig 1a. KAC 5.56 QDC 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. KAC 5.56 QDC 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. KAC 5.56 QDC 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. KAC 5.56 QDC 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Like its predecessor, the KAC QDSS-NT4 (Review 6.78), the KAC 5.56 QDC is a dedicated-bore 5.56x45mm silencer. The baffle geometry in the 5.56 QDC is similar to that in the QDSS-NT4 with two notable differences; the 5.56 QDC possesses one less baffle and also possesses additional porting. These internal differences result in the 5.56 QDC exhibiting a higher flow rate than the QDSS-NT4. This change in flow rate is observable in several waveform features presented in the above figures:
The early-time gas jetting from the 5.56 QDC is slightly delayed but higher amplitude, compared with that of the QDSS-NT4 (Figure 1b).
The rate of rise to peak positive phase impulse is significantly higher than that measured from the QDSS-NT4 (Figure 2a).
The legacy QDSS-NT4 exhibited stepped impulse accumulation (ref. Figure 2a, SSS.6.78.1.1) that was relatively erratic. The direct porting in the 5.56 QDC internal geometry increases flow rate and results in a more pronounced stepped behavior (Figure 2b). The impulse accumulation is significantly more consistent with the 5.56 QDC than with the QDSS-NT4.
PEW Science Research Note 1: The KAC 5.56 QDC exhibits some signature characteristics similar to that of the CGS Helios QD (Review 6.66). Despite the differing bore aperture and significantly different internal geometric features of the two silencers, the holistic gas flow is somewhat similar. The suppression performance on the MK18 of the 5.56 QDC and the Dead Air Nomad-30 (Review 6.100) is even more similar, though their gas flow differs greatly. When comparing the performance of the KAC 5.56 QDC to the CGS and Dead Air silencer, the two primary differences are:
The consistency of the 5.56 QDC signature.
The ability of the 5.56 QDC to achieve similar flow rate with a tighter bore aperture.
It is relatively common for a dedicated-bore 5.56 silencer to exhibit flow consistency in impulse space when fired on the standard MK18 weapon system. However, it is not as common for a dedicated-bore 5.56 silencer to exhibit as high a flow rate as the 5.56 QDC without ancillary distal venting. PEW Science postulates the high flow rate is made possible by the aforementioned early internal porting and baffle removal; the increase in consistency over the legacy QDSS-NT4 is postulated to be due to both more normalized flow through the stack at the higher rate, and improvements in manufacturing technology.
PEW Science Research Note 2: Unlike its predecessor, the KAC 5.56 QDC possesses significant first round pop (FRP) to bystanders on this weapon system. Although not as easily discernable due to the higher impulse amplitude, this FRP behavior is observed in both pressure space (Figure 1b; early jetting) and impulse space (Figure 2b; constant stepped impulse differential prior to peak accumulation). The FRP is postulated to be significant to bystanders, in accordance with PEW Science inner ear response analysis. It is likely that this pronounced FRP differential between the legacy QDSS-NT4 and newer 5.56 QDC is due to the removal of a baffle without additional flow shaping, and may be exacerbated by the porting early in the stack. Holistically, the sound signature suppression performance of the legacy KAC QDSS-NT4 is slightly higher than that of the KAC 5.56 QDC. This is reflected in the Suppression Rating calculated at both the muzzle and ear.
It is important to note that the flow rate of the KAC 5.56 QDC is much higher (the back pressure generation much lower) than some other dedicated-bore 5.56 silencers, such as the YHM Turbo T2 (Review 6.98), the Surefire SOCOM556-RC2 (Review 6.52), the SilencerCo Saker 556 (Review 6.53), and the Otter Creek Labs Polonium (Review 6.75).
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 80 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 KAC 5.56 QDC with the 3-Prong flash hider mount is 25.9 and the at-ear Suppression Rating is 22.7; the same zone on the Suppression Rating Dose Chart. The higher flow rate of the 5.56 QDC, when compared with that of some other dedicated bore 5.56x45mm silencers, allows it to produce a more balanced sound signature, between the muzzle and ear, on the standard MK18 weapon system. Regardless of this relatively balanced signature, as with the use of many silencers on the standard MK18, caution should be exercised by the weapon operator. Holistic suppression performance comparisons on the MK18 weapon system are examined in the section below.
6.104.2 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 5 presents a comparison of the PEW Science Suppression Rating of the KAC 5.56 QDC with the 3-Prong flash hider 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 KAC 5.56 QDC and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
The relatively balanced signature of the KAC 5.56 QDC on the MK18 weapon system is apparent in the above data, as well as its slight overall performance decrease when compared to its predecessor, the KAC QDSS-NT4. As discussed in the preceding section, the removal of a baffle and ancillary internal porting both act to increase the flow rate of the 5.56 QDC over that of the QDSS-NT4, but the overall sound signature suppression is slightly reduced.
The KAC 5.56 QDC exhibits a Suppression Rating at the shooter’s ear that is on-par with that of the Surefire SOCOM556-RC2 (6.52) and KGM R556 (6.60); both dedicated 5.56x45mm bore silencers with higher than average flow rates. The 5.56 QDC exhibits a higher flow rate than the SOCOM556-RC2. The sound signature of the KAC 5.56 QDC produces a hearing damage risk bystanders that is on par with the HUXWRX FLOW 556k (6.83). The Surefire SOCOM556-RC2 is significantly quieter to bystanders than the KAC 5.56 QDC and HUXWRC FLOW 556k, as reflected by the Suppression Rating at the muzzle.
PEW Science Research Note 8: The KAC 5.56 QDC does exhibit a higher flow rate than typical for a dedicated-bore 5.56 silencer. This allows the silencer to reduce the hazard to the MK18 weapon system operator when compared to silencers with more significant flow restriction, such as the SilencerCo Saker 556 (6.53), Otter Creek Labs Polonium (6.75), and YHM Turbo T2 (Review 6.98). It is interesting to note that there are silencers with somewhat higher flow restriction than the KAC 5.56 QDC that still exhibit greater sound signature suppression performance at both the muzzle and the ear, such as the CGS SCI-SIX (Review 6.101). The technologies in the silencers are significantly different; the KAC 5.56 QDC uses legacy technology with reduced baffle quantity and added porting, whereas the CGS SCI-SIX uses early porting to a more advanced geometry. The KAC 5.56 QDC may be considered an incremental evolution of the KAC QDSS-NT4 design. It is not radically different, internally, as shown in the measured holistic signature reduction performance.
Regardless of the legacy design elements in the KAC 5.56 QDC, is does exhibit balanced performance. As often stated by PEW Science, both gross suppression and overall flow rate are important contributors to the holistic signature. The signature to which the shooter’s ear is subjected is a function of both ejection port and muzzle signatures. 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.
6.104.3 Review Summary: KAC 5.56 QDC 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 KAC 5.56 QDC mounted with the 3-Prong flash hider mount achieved a composite Suppression Rating™ of 28.0 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 KAC 5.56 QDC is a full-size 5.56mm machine gun rated rifle silencer that possesses competitive sound signature suppression performance with many silencers on the current market, and achieves balanced performance on the MK18. Like its predecessor, the QDSS-NT4, the 5.56 QDC may now also be considered a legacy design. The silencer system weighs 19.9 ounces; lighter than its predecessor due to possessing one less baffle.
Despite the age of its crimped cone baffle design, the 5.56 QDC and its predecessor, the QDSS-NT4, both exhibit sound suppression performance that meets or exceeds that of some 5.56x45mm silencers on the current market, on the MK18. The baffle geometry in the 5.56 QDC is similar to that in the QDSS-NT4 with two notable differences; the 5.56 QDC possesses one less baffle and also possesses additional porting. These internal differences result in the 5.56 QDC exhibiting a higher flow rate than the QDSS-NT4. This change in flow rate is observable in the test data and analysis presented in this review.
The first-round-pop (FRP) suppression performance of the KAC 5.56 QDC is reduced when compared to that of the legacy QDSS-NT4. PEW Science postulates that the FRP differential between the two silencers is due to the removal of a baffle without additional flow shaping, and may be exacerbated by the porting early in the stack.
The mounting system of the KAC 5.56 QDC silencer is significantly different than the gate latch used with the QDSS-NT4. The QDC system uses an integral mounting collar with ball bearings that interface with sockets machined into KAC QDC muzzle devices. The muzzle devices possess an indexing pin that is received by a slot in the silencer mount interface. The pin provides a repeatable radial mounting orientation of the silencer, and when the mounting collar is tightened, the ball bearings are forced into the machined sockets on the muzzle device, preventing disengagement of the silencer. While this mount system is extremely secure and significantly less susceptible to so-called “carbon lock” than some other mounts, seizing of the silencer on the mount is still possible, and the user is encouraged to perform regular maintenance per manufacturer directive.
The KAC 5.56 QDC uses three crimped cone Inconel steel baffles. The baffle design has been scaled, both smaller and larger, for use in various Knight’s Armament silencer products through the company’s history. The silencer is extremely durable and may be used with aggressive semiautomatic and automatic firing schedules.
In this review, the 5.56 QDC 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.
