SSS.6.45 - OSS HX-QD 762 and the Q mini FIX 300 BLK Subsonic (Free Version)
/OSS HX-QD 762 on a Q mini FIX 300 BLK with 8-in Barrel
The HX-QD 762 is designed and manufactured by OSS. It is a 30 caliber centerfire rifle silencer, intended to suppress most cartridges with projectiles appropriately sized to travel through the bore, including 300 Winchester Magnum. It has a 1.62-inch diameter and is 7.1 inches in length. The silencer mounts to proprietary OSS LH-threaded taper-mount muzzle devices. The outer tube of the silencer is constructed of heat-treated 17-4 stainless steel, with the internal components being constructed of both 17-4 stainless steel and Grade 5 titanium. The silencer weighs 22.9 ounces with the Flash Hider-QD 762 taper mount, as tested. The HX-QD 762 can be obtained from Silencer Shop.
The HX-QD 762 Ti is also available, which reduces the system weight by 4.8 ounces while exhibiting similar sound suppression performance.
This review contains single-test results using the HX-QD 762 mounted with the Flash Hider-QD on the Q mini FIX bolt action pistol, chambered in 300 BLK with an 8-inch barrel. Discreet Ballistics 190gr ammunition was used in the test.
Section 6.45.1 contains the HX-QD 762 test results and analysis.
Section 6.45.2 contains Suppression Rating comparisons with selected .30 rifle silencers in the subsonic flow regime.
Section 6.45.3 contains Suppression Rating comparisons with selected .30 rifle silencers in both the subsonic and supersonic flow regimes, along with high-fidelity comparisons of the OSS HX-QD 762 performance in both flow regimes in pressure and impulse space.
Section 6.45.4 contains the review summary and PEW Science opinions.
Summary: When paired with the Q mini FIX 8” 300 BLK and fired with Discreet Ballistics 190gr Subsonic Target ammunition, the OSS HX-QD 762 with Flash Hider-QD achieved a Suppression Rating™ of 33.8 in PEW Science testing.
The supersonic .308 performance of the OSS HX-QD 762 is detailed in previous Sound Signature Review 6.41, in which it achieved a Suppression Rating of 35.1.
Relative Suppression Rating Performance is Summarized in SSS.7 - PEW Science Rankings
6.45.1 OSS HX-QD 762 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the OSS HX-QD 762 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. OSS HX-QD 762 Sound Metric Summary
6.45.1.1 SOUND SIGNATURES AT THE MUZZLE
Real sound pressure histories from a 5-shot test acquired with PEW-SOFT™ are shown below. 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, here.
Figure 1 shows a 2-millisecond long sequence of events during the first test shot with the OSS HX-QD 762, as measured 1.0 m left of the muzzle. There are four significant events shown:
During combustion within the weapon system, a 121.1 dB peak is measured.
As the precursor flow exits the silencer’s endcap vent array, a peak of 128.6 dB is measured.
Prior to muzzle blast exit, peak precursor flow is measured to reach a peak of 134.9 dB.
The maximum peak pressure amplitude of the first shot; the primary muzzle blast flow coupled with the bullet endcap exit event, is measured to be 155.8 dB.
This is a highly unusual sequence observed when firing subsonic 300 BLK ammunition from a bolt-action weapon system with an attached silencer; the precursor flow being plainly visible prior to muzzle blast is a phenomenon resulting from the extremely high flow rate of the OSS technology. As always, internal silencer design can significantly influence the measured timing and pressure amplitudes.
Fig. 1 Early-Time Shot History, OSS HX-QD 762 Bolt Action 300 BLK Muzzle Sound Pressure Signature, 20-MAR-2021
Visibility of plainly decoupled precursor flow (the pressure measured from compression and subsequent overpressure pulse through the air column in the gun barrel by the bullet prior to bullet exit) is rarely seen in the sound signature of a suppressed small arm weapon system. Typically, this phenomenon occurs nested with the post-endcap bullet exit event due to flow restriction in silencers trapping this lower pressure volumetric flow in a subsonic flow field. The OSS silencer allows this early time flow to travel relatively unimpeded through the silencer, exiting the endcap prior to the bullet leaving the silencer. By the time the bullet leaves, the muzzle blast flow is close behind and exits the multi-orifice array in the endcap. This extreme event is coupled with the bullet endcap exit, and at a peak of 155.8 dB in Figure 1, is the highest peak sound pressure from a subsonic suppressed weapon system measured by PEW Science, to date.
It is extremely important to note that while the overpressure measured 1.0 m left of the muzzle in this subsonic 300 BLK test of the OSS HX-QD 762 is higher than that measured with the same silencer in the supersonic .308 HX-QD 762 test, the actual sound signature 1.0 m left of the weapon muzzle, as interpreted by the human inner ear in this test, is on-par with that of the .308 supersonic test. This phenomenon is a byproduct of the extremely high flow rate of the silencer, and is discussed later in this article.
In addition to 300 BLK subsonic sound signature comparisons given in Section 6.45.2 of this review, subsonic and supersonic flow comparisons are discussed in Section 6.45.3.
The primary sound signature pressure histories for all 5 shots are shown in Figure 2a. A zoomed-in timescale displays the region of peak sound pressure in Figure 2b, for the first two shots. The real sound impulse (momentum transfer potential) histories from the same 5-shot test are shown in Figure 3. Again, full and short timescales are shown.
Fig 2a. OSS HX-QD 762 Bolt Action 300 BLK Muzzle Sound Pressure Signature, 20-MAR-2021
Fig 2b. OSS HX-QD 762 Bolt Action 300 BLK Muzzle Sound Pressure Signature, Short Time Window, 20-MAR-2021
Figure 3a. OSS HX-QD 762 Bolt Action 300 BLK Muzzle Sound Impulse Signature, 20-MAR-2021
Figure 3b. OSS HX-QD 762 Bolt Action 300 BLK Muzzle Sound Impulse Signature, 20-MAR-2021
As discussed in the previous supersonic .308 test analysis, and above, the OSS HX-QD 762 exhibits extremely high flow rate. The flow rate out of the silencer is so fast, and the duration of the smaller subsonic 300 BLK case charge load so much lower than .308, that the sound overpressure decay to ambient happens prior to ground reflection. This phenomenon is shown in Figure 2a, in which the ground reflection to the sensor is visible at approximately 37 ms. Typically, with longer duration combustion (.308, for example) this reflection coalesces with the continued gas blowdown out of the silencer, as seen in the .308 test of this silencer, and other high-flow silencers with .308, like the Dead Air Sandman-K in Sound Signature Review 6.15.
PEW Science Note 1: Interestingly, even with the radically high flow rate of the OSS HX-QD 762, Figure 2b shows a slight pressure regime first-round-pop (FRP) and Figure 3 shows a more exaggerated FRP in impulse space. The first round pop with subsonic 300 BLK is postulated to be significantly noticeable to bystanders, as determined by PEW Science inner-ear response analysis.
PEW Science Note 2: With each subsequent shot, the peak positive phase impulse is measured to decrease, as shown in Figure 3b. This phenomenon is not yet well studied by PEW Science with the OSS silencer and it does not occur in the supersonic flow regime; it appears to be isolated to shorter duration subsonic flow with this silencer. PEW Science postulates that due to the lower pressure and shorter duration of subsonic 300 BLK cartridge combustion, the flow cavities in the OSS design may not be fully utilized when compared to longer duration, higher pressure flow. Also, the silencer does not necessarily get quieter to bystanders with subsequent shots, but it does get quieter to the shooter. These phenomena are the subject of further study.
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.
With subsonic 300 BLK from an 8-inch barrel, the OSS HX-QD is only nominally quieter to bystanders than it is with supersonic .308 from a 20-in barrel. Direct comparisons are provided in Section 6.45.2 and 6.45.3, below. The FRP of the HX-QD 762 on subsonic 300 BLK is significant to bystanders and shooters, as determined by PEW Science inner ear modeling, whereas it is not significant with supersonic .308 to either parties. This silencer represents a significant deviation in sound suppression mechanism from others on the market. The intended use of the HX-QD 762 silencer is to reduce back pressure with a high mass flow rate, and reduce sound signature as much as practical for the flow rate achieved. The physical consequence of this is relatively poor subsonic sound suppression.
PEW Science Note: The OSS HX-QD 762 is an inefficient subsonic rifle silencer. In the subsonic flow regime, lower mass flow rate (trapping gas) is a primary mechanism of sound signature suppression. As the OSS design exhibits relatively high mass flow rate, its subsonic suppression capability is less than optimal when compared to many other silencers in this market segment. Furthermore, there are other silencers that achieve high mass flow rate though different design mechanisms (e.g. large orifice size) that still may excel at subsonic flow suppression.
Comparisons with other silencers in the subsonic flow regime are shown in Section 6.45.2, with the supersonic and subsonic comparisons of the HX-QD 762 shown in Section 6.45.3.
6.45.2 Suppression Rating Comparison - Subsonic 300 BLK
The OSS HX-QD 762 suppressor is intended to possess high mass flow rate (low back pressure; low PEW Science Omega metric) while exhibiting as much sound suppression as is practical (maximizing PEW Science Suppression Rating). As previously discussed, its subsonic sound signature suppression performance is less than optimal. Figure 6 shows a performance comparison of the seven .30 rifle silencer configurations tested with the subsonic 300 BLK cartridge shown in public PEW Science testing, to date. Unsuppressed and suppressed Suppression Ratings are shown for both the shooter and bystanders.
Figure 6. Suppression Rating Comparisons Of .30 Rifle Silencers Using PEW-SOFT 300 BLK Subsonic Test Data
The mass flow rate of the OSS HX-QD 762 is too high, and the 8-in 300BLK test host barrel too short, to effectively suppress subsonic 300 BLK when compared to many other mid-size .30 silencers on the market. As stated previously in this review, this is a physical consequence of the silencer’s design. The Suppression Rating 1.0 m left of the endcap is two categories lower than most of the silencers shown in Figure 6, and both the muzzle and ear Suppression Ratings are three categories lower than that of the Sig SRD762Ti-QD (Review 6.39), which represents an extremely significant gap in sound suppression performance. Even the compact YHM Resonator K (Review 6.30) is quieter than the HX-QD 762 with subsonic 300 BLK, despite the HX-QD being quieter than the Resonator K with supersonic .308 (see Section 6.45.3). Again, this is a consequence of the OSS HX-QD design; it is a purpose-built high mass flow rate silencer intended for use with the high pressures generated with supersonic cartridges.
It is important to note that the propensity of a rifle silencer to exhibit differing sound signature suppression in the supersonic and subsonic flow regimes is typical. However, when the performance in the flow regimes varies drastically, as is the case with the OSS HX-QD 762, it typically occurs due to the primary mechanism of suppression varying significantly. To illustrate the differing sound suppression phenomena, detailed comparative analysis of the HX-QD 762 in both flow regimes is presented below, along with summary data for two other silencers.
6.45.3 Suppression Rating Comparison - Subsonic 300 BLK vs. Supersonic .308
The sound suppression performance of three silencers in both the supersonic and subsonic flow regimes are compared in Figure 7, below. The solid colors in the plot denote supersonic .308 performance, whereas the typical shaded patterns denote subsonic 300 BLK performance. As the PEW Science Suppression Rating is a universal sound signature metric based upon the response of the human inner ear, all metrics in this plot are comparable to each other, regardless of cartridge. The PEW Science Suppression Rating is the only sound signature metric that allows the comparison of human inner ear response to fast transients, across all suppressed weapon system platforms.
Figure 7. Suppression Rating Comparisons Of .30 Rifle Silencers Using PEW-SOFT 300 BLK Subsonic and .308 Supersonic Test Data
The immediate conclusion presented in Figure 7 is that the sound suppression performance of the OSS HX-QD 762 hits a maximum threshold. As the silencer is unable to trap gas, and must use other mechanisms for primary sound signature suppression, such as heat dissipation, the lower flow pressure and mass flow rate of the subsonic 300 BLK cartridge does little to help its suppression performance.
The contrast in the performance of other silencer designs is significant; even with small, relatively loud silencers like the YHM Resonator K and Energetic Armament VOX S (multiple reviews), their performance increase with the use of subsonic 300 BLK when compared with supersonic .308 is significant. Those silencers are able to trap gas; it is their primary sound suppression mechanism. The VOX S, for example, represents a silencer design that has an almost reversed flow efficiency compared with the OSS HX-QD 762. Where the OSS design excels at supersonic suppression performance with a high mass flow rate resulting in extremely low back pressure (at the expense of subsonic performance) the Energetic Armament VOX S has lower mass flow rate, relatively high back pressure, and relatively poor supersonic suppression performance, but adequate subsonic sound signature suppression for its size. The OSS design is extremely complex; the Energetic Armament design is extremely simple. The two silencers, therefore, represent almost opposite ends of the efficiency spectrum for both flow regime and design envelope. Neither silencer excels in both categories. The YHM Resonator K, for its size, is actually the most balanced silencer shown in Figure 7, due to its significantly lower back pressure than the Energetic Armament VOX S, with higher subsonic suppression performance than the OSS HX-QD 762.
PEW Science Research Note: It may be difficult for the reader to reconcile the performance differentials shown in Figure 7; PEW Science postulates that most readers and silencer users have never been presented with information indicating that silencers perform differently in different flow regimes, anecdotal experience notwithstanding. To further illustrate the physical behavior of the OSS HX-QD 762 design, detailed waveform comparisons of the silencer in both flow regimes are presented below.
Figure 8a presents the first round sound signatures of the OSS HX-QD 762 silencer in the supersonic and subsonic flow regimes, respectively, in pressure space. The same comparison is shown in impulse space, in Figure 8b.
Figure 8a. OSS HX-QD 762 Supersonic .308 And Subsonic 300BLK Bolt Action Rifle Muzzle Sound Pressure Signature Comparison (FRP)
Figure 8b. OSS HX-QD 762 Supersonic .308 And Subsonic 300BLK Bolt Action Rifle Muzzle Sound Impulse Signature Comparison (FRP)
The OSS HX-QD exhibits higher peak sound pressure with subsonic 300 BLK from an 8-in barrel, than it does with supersonic .308 from a 20-in barrel, by a significant margin (Figure 8a). However, the opposite relationship holds true in impulse space (Figure 8b). This is a direct illustration of two phenomena:
The high flow rate of the OSS HX-QD762 is clear, as previously discussed; the precursor flow (the pressure measured from compression and subsequent overpressure pulse through the air column in the gun barrel by the bullet prior to bullet exit, and this pressure being expelled into the silencer and out of the endcap) is plainly visible in pressure space before the bullet and muzzle blast exit during subsonic flow. This also appears in impulse space as early time positive phase impulse accumulation. The HX-QD 762 lets flow out of the silencer too quickly for subsonic suppression to be effective.
The heat dissipation and other energy transfer mechanisms in the OSS silencer are not efficiently utilized until a minimum flow pressure and velocity threshold is achieved. The internal geometry of the HX-QD is not effectively utilized under a certain flow velocity and pressure threshold.
To illustrate that the above phenomena are not artifacts of ancillary internal combustion from FRP, the exercise is repeated below in Figure 9a and Figure 9b.
Figure 9a. OSS HX-QD 762 Supersonic .308 And Subsonic 300BLK Bolt Action Rifle Muzzle Sound Pressure Signature Comparison (Shot 2)
Figure 9b. OSS HX-QD 762 Supersonic .308 And Subsonic 300BLK Bolt Action Rifle Muzzle Sound Pressure Signature Comparison (Shot 2)
The exact same phenomena observed during Shot 1 in both supersonic and subsonic flow regimes with the HX-QD that were observed in Figure 8 are again observed in Figure 9. Regardless of internal atmosphere, the OSS HX-QD is inefficient at subsonic sound signature suppression when compared to supersonic flow.
The OSS silencer technology is not the only silencer technology that exhibits deficiency in one flow regime. As previously stated, the Energetic Armament VOX S exhibits the opposite deficiency, as do other silencers with simple straight cone designs, such as the Q Trash Panda (Review 6.4), albeit to a lesser degree. Silencers like the Trash Panda make up for supersonic flow suppression deficiencies with larger volume; a serendipitous performance balance with utility that only stretches so far. Internal volumetric increases typically assist significantly with subsonic flow suppression, all other things equal. The balance of supersonic and subsonic suppression performance of small arm weapon system silencers is a subject of ongoing PEW Science research.
6.45.4 Review Summary: OSS HX-QD 762 on a Q mini FIX 300 BLK with 8-in Barrel
When paired with the Q mini FIX 8” 300 BLK and fired with Discreet Ballistics 190gr Subsonic Target ammunition, the OSS HX-QD 762 with Flash Hider-QD achieved a Suppression Rating™ of 33.8 in PEW Science testing.
PEW Science Subjective Opinion:
The OSS HX-QD 762 is a mid-size, relatively heavy, and durable .30 rifle silencer that exhibits class-leading back pressure reduction with a notable balance of sound signature suppression performance in the supersonic flow regime, but relatively inefficient sound signature suppression performance in the subsonic flow regime. The HX-QD 762 is also offered in a titanium version which reduces the weight of the system by almost 5 ounces; its sound suppression parameters in both flow regimes are similar to those of the steel version. Users should note that most silencers exhibit significantly different sound suppression characteristics in different flow velocity and pressure regimes, i.e. when suppressing supersonic vs. subsonic cartridges. This sound suppression performance variation, across different flow regimes, is more pronounced with silencers possessing high flow rate (low back pressure) characteristics, like the HX-QD 762.
The HX-QD 762 contains a series of ported helical baffle components within the silencer core. Functionally, the core uses geometric features to induce turbulent flow, while early and continuously routing combustion gasses into annular space for down-stream venting to atmosphere. The distal end of the silencer contains significant exit flow area around its outer circumference. The sound suppression efficiency of this design is directly proportional to cartridge pressure, flow velocity, and duration.
The aforementioned method by which the HX-QD 762 shapes gas flow and allows it to exit the silencer is significantly different than many silencers on the current market. As shown in this review, the flow characteristics of the silencer significantly reduce efficiency in the subsonic flow regime when compared to the supersonic flow regime. While the OSS HX-QD 762 represents the best balance of Suppression Rating and back pressure reduction in the supersonic flow regime measured by PEW Science, it provides an excellent case study on how difficult it is to suppress a subsonic cartridge like 300 BLK without trapping gas.
The left-hand (LH) threaded taper mounts from OSS are simple to operate. They may be installed on the weapon system with an adjustable wrench; the mount bodies, themselves, serve as wrench-flats. The mount sits flush with the rear of the silencer when fully installed; there is no mount protrusion. As the silencer is LH threaded to the mount, the mount is easily removed from the silencer, should the mount be detached from the weapon while still in the silencer. One can then tighten the entire assembly to the conventionally right-hand (RH) threaded barrel muzzle, and continued RH tightening will subsequently loosen the silencer from the mount. Although proper mount installation torque mitigates such a solution from being absolutely necessary, this mechanical feature is welcome for practicality.
The silencer is also offered in a titanium version, as stated above. The Ti version may be attractive to some users due to the weight reduction; PEW Science has tested the Ti version and noted similar Suppression Rating performance to the steel version tested. Durability of the steel silencer is expected to be higher than that of the Ti silencer. PEW Science has not evaluated the durability of the HX-QD 762 silencer system(s) on semiautomatic or automatic host weapons. Note that the nature of low flow restriction (low back pressure) silencers may influence durability. These phenomena are subjects of further research.
In this review, the OSS HX-QD 762 performance metrics depend upon suppressing a subsonic intermediate rifle cartridge. While the sound signature of such cartridges can be suppressed to levels that may result in the desire of the shooter and bystanders to not wear hearing protection, PEW Science encourages the reader to remain vigilant with regard to all subsonic rifle cartridge suppression claims. The gas volume and combustion products created by firing a subsonic intermediate rifle cartridge such as 300 BLK are still significant; the measured pressure and impulse magnitudes, and their durations, illustrate this fact. The subsonic suppression performance of the HX-QD 762 is lower than other silencers of similar size.
The hearing damage potential of subsonic rifle use is not insignificant. PEW Science encourages the reader to consider the Suppression Rating when deciding on an appropriate silencer and host weapon combination for their desired use.
