SSS.6.126 - Liberty Precision Machine Torch and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle
/Liberty Precision Machine Torch on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The Torch is manufactured by Liberty Precision Machine (LPM). It is a 6mm centerfire rifle silencer, intended to suppress the 5.56x45mm cartridge on barrels as short as 7.5 inches in length. The Torch is has a modular end cap; it may be used with both the included solid and vented end caps that both possess flash-hiding features. It has a 1.74-inch diameter and is 6.2 inches long with no mount. The rear of the silencer is threaded with the so-called HUB universal diameter and pitch, allowing the use of a variety of mounting solutions. With the included direct thread mount, the silencer’s length increases to 6.4 inches. The silencer is tubeless and all welded components are 17-4 stainless steel. The Torch uses a serial-ID ring on the rear portion of the silencer, under license. The silencer weighs 14 ounces, and the included titanium direct thread mount weighs 0.8 ounces, for a total system weight of 14.8 ounces, as tested. The Torch can be obtained from Liberty Precision Machine.
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 for public research 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 data production for this Sound Signature Review white paper was funded in part by PEW Science Project PEW-LPM-064-001-23. Therefore, data pertaining to the Torch in this Sound Signature Review is published with the express written permission of Liberty Precision Machine, LLC.
This Sound Signature Review contains the results from two tests using the Torch with the direct thread 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 tests. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Section 6.126.1 contains the Torch Solid End Cap Configuration test results and analysis.
Section 6.126.2 contains the Torch Vented End Cap Configuration test results and analysis.
Section 6.126.3 contains Suppression Rating comparisons of the Torch in both configurations with dedicated 223 and 30 caliber silencers on the current market, including the PWS BDE 556, CAT ODB, Aero Precision Lahar-30L, Lahar-30, HUXWRX FLOW 762 Ti, Maxim Defense DSX, Thunder Beast Dominus, KAC 5.56 QDC, CGS SCI-SIX, Dead Air Nomad-30, YHM Turbo T2, Dead Air Sandman-S, HUXWRX FLOW 556k, Energetic Armament ARX, KAC QDSS-NT4, Rugged Razor556, Otter Creek Labs Polonium and Polonium-K, Surefire SOCOM556-RC2, HUXWRX HX-QD 556 and HX-QD 556k, Q Trash Panda, CGS Helios QD, SilencerCo Saker 556, Rugged Razor762, and others.
Section 6.126.4 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the LPM Torch with its solid end cap achieved a composite Suppression Rating™ of 35.9 in PEW Science testing. With its vented end cap installed, the Torch achieved a Suppression Rating of 29.8.
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
6.126.1 Liberty Precision Machine Torch (Solid End Cap) Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the Torch with its solid end cap is shown in Table 1. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. This is a members-only review and includes pressure and impulse waveforms measured at the shooter’s ear. PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
Table 1. Liberty Precision Machine Torch (Solid End Cap) Sound Metric Summary
6.126.1.1 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 Torch in its solid end cap configuration 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. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
With its solid end cap, the LPM Torch exhibits high muzzle signature suppression performance and a relatively consistent gas momentum profile (Figure 2) on the 5.56x45mm MK18 weapon system. Although the measured gas momentum at the muzzle during first round pop (FRP) is significant, it may not be interpreted as severe to bystanders, in accordance with PEW Science inner ear modeling.
Like many centerfire rifle silencers exhibiting a high degree of muzzle suppression, the measured early-time signatures of the Torch are consistent. Divergence occurs upon primary jetting, in which the vented paths in the silencer’s baffle stack are purged throughout the shot string. For a 6mm silencer, the rate of rise to maximum positive phase impulse is high, achieving a rate nominally faster than the Surefire SOCOM556-RC2 (6.52). The gross signature severity at the muzzle from both silencers is very similar. Both silencers also utilize early-time venting, though they do so with drastically different geometry.
PEW Science Research Note 1: The LPM Torch uses a vented blast baffle with an oversized primary orifice. The baffles possess annular cavities and are best described as “progressively ported.” With respect to early time gas dynamics, this “nested” blast baffle configuration alters both the shock reflections from primary muzzle blast as well as the gas phase, potentially lowering the impact of the silencer on the kinematics of a host weapon like the the standard MK18 weapon system. This potential may be realized regardless of end cap choice. This purposeful alpha parameter minimization employed by LPM also has the consequence of potentially reducing blast baffle erosion due to the geometry of primary jet impingement. However, it should be noted that muzzle device may significantly play a role in this behavior. The jet expansion from the free orifice in the direct thread mount used in this test should be considered a baseline case. Mount changes may alter the benefits of these early-time gas dynamics.
PEW Science Research Note 2: The gas dynamics of the Torch do not completely normalize until after Shot 2; note the slightly shallower initial slope, beginning with Shot 3 in Figure 2. It is postulated that this behavior is indicative of slight nonuniformity in gas flow due to the porting design in the silencer baffles or annular space. When gross flow rate is increased, measurement of the phenomenon is exacerbated. Those gas dynamics are examined in Section 6.126.2 with the vented end cap.
PEW Science Research Note 3: The silencer possesses lower effective back pressure in early-time than typical 5.56x45mm silencers, even with its solid end cap. For example, the Torch produces lower bolt speed on the MK18 than both the Otter Creek Labs Polonium (6.75) and the SilencerCo Saker 556 (6.53). The Polonium is also a 6mm silencer. Both the Polonium and the Saker share a similar blast baffle design geometry. As described above, the blast baffle design of the Torch is unique. The Torch produces a less severe signature at the operator’s head on the untuned MK18 weapon system than both of those silencers, regardless of end cap. Resulting gas dynamics measured at the shooter’s ear with the Torch are included in the PEW Science Member version of this review. For weapon function, the Liberty Precision Machine Torch with its solid end cap can best be compared to the CGS SCI-SIX (6.101) on the standard MK18. The two silencers produce extremely similar effective weapon kinematics, though the ejection port signatures they produce differ. This is further discussed in Section 6.126.1.2.
PEW Science Research Note 4: As in all semiautomatic AR15 weapon testing, a second pressure pulse originates from the ejection-port signature of the weapon and it occurs early enough in time such that its waves coalesce with that of the muzzle signature. However, in late time (at approximately 81 ms in Figure 1a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 does not display this event due to the bolt remaining open after the sixth and final round is fired from the magazine.
PEW Science Research Note 5: The closing time of the MK18 bolt is directly related to the flow restriction of a silencer for a given weapon system. PEW Science has determined bolt closing time variation from the unsuppressed state to be a reliable indicator of silencer back pressure, with strong correlation with the PEW Science Back Pressure Metric, Omega and the alpha parameter. However, PEW Science has also determined that the indicator is unreliable upon upper receiver fouling. Sound signatures are not influenced by this fouling, as these kinematics occur in late time, after gas venting to atmosphere. Momentum transfer, weapon condition (upper receiver fouling), and other factors, can significantly influence bolt closing time. PEW Science urges the reader to exercise extreme caution if using the published bolt closing time to make determinations regarding silencer flow restriction (back pressure) or weapon system kinematics. This type of calculation may provide erroneous results, as the weapon condition at the time of each test is not published data. The time-scale duration showing bolt closing time is only published by PEW Science such that the signature data pedigree may be verified.
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 6: Note that the muzzle Suppression Rating of the Torch with its solid end cap is 35.6 and the at-ear Suppression Rating is 22.4; different zones on the Suppression Rating Dose Chart. The back pressure of the Torch contributes to a more severe ejection port signature, increasing the overall severity of the signature to the shooter on the standard MK18 weapon system. The vented end cap may be used to reduce this shooter hazard, though there are tradeoffs to overall performance, which are examined in Section 6.126.2.
The signatures measured at the shooter’s ear are presented below.
6.126.1.2 SOUND SIGNATURES AT SHOOTER’S EAR
Real sound pressure histories from the same 6-shot test acquired with PEW-SOFT at the shooter’s ear are shown below. Again, the waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science testing is 1.0 MS/s (1 MHz).
The primary sound signature pressure histories at the ear for all 6 shots are shown in Figure 3. The primary sound signature history is shown in Figure 3a. An annotated timescale is displayed in Figure 3b, for Shots 1 and, 2. The real sound impulse (momentum transfer potential) histories at the ear from the same 6-shot test are shown in Figure 4. Again, full and short timescales are shown.
Figure 3a. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature
Figure 3b. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Figure 4a. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature
Figure 4b. Liberty Precision Machine Torch (Solid End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature Peaks
Like at the muzzle, the FRP at the shooter’s ear is measurable. But, also like at the muzzle, PEW Science inner ear modeling indicates a relatively low FRP severity to the shooter, relative to subsequent shots. Ejection port signature contributes to shooter hazard throughout the shot string.
PEW Science Research Note 7: There is a significantly prolonged gas momentum accumulation plateau measured at the shooter’s ear during the first shot (Figure 4b). As previously mentioned, it is not extremely severe relative to subsequent shots, but is noticeable. The primary contributor to this momentum accumulation plateau is FRP muzzle blast.
The shooter’s ear Suppression Rating of the Torch with its solid end cap is similar to that of the SOCOM556-RC2 on this host, and there are features in the waveforms measured at the shooter’s ear that indicate gross weapon kinematics are also extremely similar. The low amplitude of pressure blowdown earlier in time, which allows carrier group impact with the receiver extension to be visualized (Figure 3b) is one indicator. The return of the carrier group to battery is another.
PEW Science Research Note 8: One differentiator between the shooter’s ear waveforms of the solid end cap Torch and the SOCOM556-RC2 is the FRP impulse accumulation and its front or back loaded nature, depending on the silencer. The SOCOM556-RC2 is slightly more balanced. This phenomenon is discussed in the MK18 vs. SURG tuning comparison in article 6.111 (Maxim DSX SURG). Regardless of this phenomenon that presents in FRP in this test of the Torch, the Torch is a relatively balanced silencer when compared to that of the RC2, even with less robust FRP control than the RC2.
As discussed in the preceding section, the LPM Torch with its solid end cap and the CGS SCI-SIX produce extremely similar effective weapon kinematics, though the ejection port signatures they produce differ. Members are encouraged to examine the impulse histories measured at the shooter’s ear with the selected SCI-SIX variant and note the front-loaded FRP behavior. The ejection port signature from the solid end cap Torch system has slightly more severe ejection port blast, which is one of the reasons for the lower operator hazard when using the SCI-SIX on the standard MK18.
PEW Science Research Note 9: It is likely that if the standard MK18 weapon system is tuned, the Torch silencer system with its solid end cap will achieve nominally higher levels of suppression performance at the shooter’s ear. Weapon tuning is outside the scope of this article. However, the reader is referred to the aforementioned SURG study for the benefits of such weapon tuning, as applied to the 10.3-in 5.56x45mm automatic rifle. In that test series, effective gas port size as the variable is shown to significantly change signature hazard to the operator. Manufacturer feedback from Liberty Precision Machine indicates that more gas impulse from an adjustable gas block is needed to tune a weapon than with some other silencers. PEW Science postulates that this is most likely due to the extremely low alpha parameter of the torch; the shock reflections are redirected in early time. Without the early time contribution to the rearward impulse propagation from these reflections, the gas phase becomes of greater importance to the total impulse load to cycle the weapon. Therefore, the system behaves like a lower backpressure silencer for function, but not necessarily for blowback, with the solid end cap. This is an excellent, practical example of alpha and Omega variance, and the differences in performance when isolating changes in those two parameters.
6.126.2 Liberty Precision Machine Torch (Vented End Cap) Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the Torch with its vented end cap is shown in Table 2. The data acquired 1.0 m (39.4 in) left of the muzzle is available for viewing to all. As stated in Section 6.126.1, this is a members-only review and includes pressure and impulse waveforms measured at the shooter’s ear. PEW Science thanks you for your support; further testing, research, and development of PEW-SOFT and the Silencer Sound Standard is made possible by members like you!
Table 2. Liberty Precision Machine Torch (Vented End Cap) Sound Metric Summary
6.126.2.1 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.
The primary sound signature pressure histories for all 6 shots with the Torch with its vented end cap are shown in Figure 5a. The sound signatures of Shot 1 and Shot 2 are shown in a smaller time window in Figure 5b. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 6a. In Figure 6b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shot 2, Shot 3, and Shot 4.
Fig 5a. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 5b. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature, Short Time Window
Fig 6a. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Fig 6b. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature, Short Time Window
One thing that is immediately apparent upon examination of the signatures measured at the muzzle from the vented configuration of the Torch is that gas momentum is drastically increased. The larger orifice in the vented end cap allows for both the primary and annular jetting to exit the silencer at a higher velocity. This higher particle velocity builds momentum earlier in time, and is responsible for the faster pressure rise in Figure 5 and steeper impulse accumulation rates shown in Figure 6.
PEW Science Research Note 10: Another significant difference between the behavior of the Torch with its solid and vented end caps is its signature consistency. Like other silencers utilizing modular end caps to further access venting arrays, combustion propagation can sometimes be erratic throughout the shot string. This phenomenon was noted in the MK18 testing of the CGS Helios QD (6.66), only in its vented configuration, and for only two shots. The design of that silencer is different than that of the Torch, and it is also significantly over-bored for the cartridge. This type of erratic combustion propagation can also occur in over-bored silencers even if they do not possess venting. An example of a system with primitive baffles designs exhibiting that behavior on this weapon system is the Dead Air Sandman-S (6.92) in which combustion propagation becomes erratic as the shot string continues. In the case of the Torch, gas momentum is erratic immediately after FRP. PEW Science postulates that the phenomenon discussed in Research Note 2 in the test of the solid end cap configuration of the Torch is exacerbated with larger flow area at the distal orifice.
PEW Science Research Note 11: During FRP, the signature exhibits a less pronounced momentum accumulation plateau (Figure 6b). The rarefaction that produces this later time consistency does not present in subsequent shots until after Shot 4. Again, this indicates erratic behavior, otherwise defined as signature inconsistency that presents similarly to over-bore. Such inconsistency characterized in measured impulse signatures from over-bored silencers may be examined in test reports featuring products such as the Rugged Razor762 (6.58), the Energetic Armament ARX (6.82), the Rugged Razor556 (6.76), the Q Trash Panda (6.61), and the aforementioned Dead Air Sandman-S (6.92). Despite exhibiting somewhat similar erratic behavior, the vented configuration of the Torch still outperforms all of those silencers in gross muzzle suppression on the standard MK18 weapon system, except for the Trash Panda which nominally outperforms the vented configuration of the Torch at the muzzle.
The severity of the signature from the Torch does increase with its vented end cap. However, its muzzle signature suppression performance still eclipses that of many other silencers tested on the MK18, including the CGS Helios QD (6.66), HUXWRX FLOW 556k (6.83), KAC 5.56 QDC (6.104), Thunder Beast Dominus SR (6.105), Rugged Razor556 (6.76), Dead Air Sandman-S (6.92), and the Energetic Armament ARX (6.82).
The gross flow rate of the Torch also increases with the use of the vented end cap. For PEW Science members, the signatures at the shooter’s ear with the vented configuration of the Torch are presented. The combination of high early-time flow rate (lower alpha) with the lowering of distal restriction (dropping Omega) can sometimes achieve a desired increase in flow rate to reduce operator hazard on systems in which such hazard is dominated by ejection port signature.
6.126.2.2 SOUND SIGNATURES AT SHOOTER’S EAR
Real sound pressure histories from the same 6-shot test acquired with PEW-SOFT at the shooter’s ear are shown below. Again, the waveforms are not averaged, decimated, or filtered. The data acquisition rate used in all PEW Science testing is 1.0 MS/s (1 MHz).
The primary sound signature pressure histories at the ear for all 6 shots with the Torch in its vented configuration are shown in Figure 7a. A zoomed-in timescale is displayed in Figure 7b, in the region of peak sound pressure. The real sound impulse (momentum transfer potential) histories at the ear from the same 6-shot test are shown in Figure 8.
Fig 7a. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature
Fig 7b. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Fig 8a. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature
Fig 8b. Liberty Precision Machine Torch (Vented End Cap) 5.56x45mm NATO MK18 Automatic Rifle Ear Sound Impulse Signature, Short Time Window
It is clear, from the above data, that the vented end cap of the Torch reduces effective silencer back pressure. Operator hazard is also reduced; the ejection port blast contribution to the signature measured at the operator’s head is reduced. Note the lower pressure blowdown amplitude at approximately 45 ms in Figure 7b. Compare this signature region to that of the same measured with the solid end cap in Figure 3b. Ejection port blast duration has dropped. This is a result of the bolt carrier group staying closed slightly longer; the bolt speed reduction is also visible (its impact on the receiver extension happens later and it returns to batter later than with the solid end cap). The vented end cap reduces ejection port blast hazard to the operator, with this specific silencer in this specific weapon configuration.
PEW Science Research Note 12: There is no “free lunch” with some silencer technologies. The LPM Torch design utilizes a nested vented blast baffle array to redirect early time shock and allow early time gas phase propagation forward. However, the silencer’s baffle design is still somewhat conventional even with the use of annular cavities. The distal venting of a portion of these cavities with a larger distal orifice (a vented end cap) combines with its early time behavior to produce an overall flow rate conducive to a reduction in ejection port blast by altering weapon kinematics less-so than a conventional rifle silencer. However, the distal venting is largely uncontrolled. This is not a multistage silencer and although it is somewhat of a hybrid design with its baffle vent arrays, it is less advanced than some other designs. The distal orifice gas propagation is still severe, which lowers its muzzle Suppression Rating significantly with the vented end cap, compared to with the solid end cap.
Although the signature does get more severe to bystanders, the vented end cap results in a system that is nominally similar to that of the HUXWRX (OSS) HX-QD 556 (6.54) on this weapon system. For a silencer with a largely conventional, though annularly ported, baffle design to achieve such balance on the standard MK18, is notable.
PEW Science Research Note 13: There may be advantages to achieving the gross Suppression Rating balance seen in the vented Torch system performance in the way it is achieved, compared to way the HX-QD 556 performance is achieved with so-called Helix Flow-Through technology. PEW Science research is ongoing. The following phenomena may significantly influence sound-field:
Distal gas velocity gradients.
Gas velocity vector shapes.
Wave shape-dependent reflection factors.
PEW Science laboratory research focuses on various phenomena, including the above. Many of these phenomena are outside the scope of the public data presentation in the Silencer Sound Standard. As more technologies are publicly presented, the phenomena will increase in relevance to the Standard. For example, firing weapons in enclosed spaces presents hazards that can scale nonlinearly and differently with different technologies.
The Torch in its vented configuration is less damaging to the shooter’s ear, due to somewhat lower backpressure. However, it is also more severe to bystanders.
6.126.3 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 9 presents a comparison of the PEW Science Suppression Rating of the two configurations of the Liberty Precision Machine Torch 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 9. Suppression Rating Comparisons of the Liberty Precision Machine Torch (with solid and Vented End Caps) and other silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 9 presents detailed PEW Science Suppression Ratings, computed at the muzzle and ear, for the listed silencers. The Suppression Rating is a holistic parameter that captures human inner ear damage risk potential from a measured impulsive overpressure signature during the entire time regime of weapon operation, including combustion, complete blowdown, and all mechanical operation, including the carrier group returning the battery, in the true free field. The parameter may be used with the dose chart at the beginning of this report.
The overall performance of the Liberty Precision Machine Torch on the standard MK18 is best summarized by the following:
With its solid end cap, the Torch produces a sound field extremely similar in severity to that of the Surefire SOCOM556-RC2 (6.52) on this weapon system.
With its vented end cap, the Torch’s signature severity is very similar to that of the HUXWRX (OSS) HX-QD 556 (6.54) on this weapon system. It is important to note that severity comparisons are valid in the free field. Further research is being conducted on the efficacy of different high flow system technologies and the respective hazards produced near reflecting surfaces.
The Torch produces lower bolt speed on the MK18 than both the Otter Creek Labs Polonium (6.75) and the SilencerCo Saker 556 (6.53). Like the Polonium, the Torch is also a 6mm silencer. Both the Polonium and the Saker share a similar blast baffle design geometry. As previously described in this report, the blast baffle design of the Torch is unique. The Torch produces a less severe signature at the operator’s head on the untuned MK18 weapon system than both of those silencers, regardless of end cap.
The severity of the signature from the Torch does increase with its vented end cap. However, its muzzle signature suppression performance still eclipses that of many other silencers tested on the MK18, including the CGS Helios QD (6.66), HUXWRX FLOW 556k (6.83), KAC 5.56 QDC (6.104), Thunder Beast Dominus SR (6.105), Rugged Razor556 (6.76), Dead Air Sandman-S (6.92), and the Energetic Armament ARX (6.82).
Although less weapon tuning may be needed with its solid end cap configuration than with other silencers, the vented end cap configuration of the Torch provides superior reduction of ejection port blast hazard to the weapon operator with this silencer.
The Liberty Precision Machine Torch represents a flexible design with modularity in its end cap configurations that enable spanning a relatively large range of use cases for the AR-15 weapon system.
PEW Science Research Note 14: The Torch, in both of its end cap configurations, outperforms many silencers tested on the MK18 by PEW Science, to date, in signature hazard reduction to bystanders, the weapon operator, or both. Due to the breadth of the Silencer Sound Standard testing and analysis pedigree, the reader is encouraged to examine the spectrum over which suppression performance on the MK18 has been demonstrated. There exist silencers evaluated on the 5.56x45mm short barrel rifle platform that have significantly lower performance. Because the PEW Science Suppression Rating is a damage risk criterion (DRC), a lower Suppression Rating indicates a higher personnel hazard in the free field - it is not a subjective quantity; it is an objective quantification of hearing damage risk potential.
As shown in Figure 9, the Suppression Rating at the shooter’s ear may be significantly influenced by the ejection port signature from the MK18; all other things equal. For details on performance increases that are possible when “tuning” an AR-15 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-15 weapon system. Specific weapon system parameters will dictate modification efficacy.
6.126.4 Review Summary: Liberty Precision Machine Torch 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 LPM Torch with its solid end cap achieved a composite Suppression Rating™ of 35.9 in PEW Science testing. With its vented end cap installed, the Torch achieved a Suppression Rating of 29.8. As with all weapon systems, the user is encouraged to examine both muzzle and ear Suppression Ratings.
PEW Science Laboratory Staff Opinion:
The Liberty Precision Machine Torch is a full size 6mm centerfire rifle silencer that may be configured with the included solid or vented flash hiding end caps to allow the user to adapt it to various weapon systems. The silencer possesses high gross suppression performance and may also be adapted to mimic holistic signature performance of a Flow-Through silencer. The Torch is stainless steel, possesses a nested blast baffle, and its gas dynamics allow for less over function of the AR-15 platform. The silencer also possesses a modular rear mounting interface that may be used with a variety of mounting solutions and muzzle devices.
The LPM Torch represents a flexible design with modularity in its end cap configurations that enable spanning a relatively large range of use cases for the AR-15 weapon system. With its solid end cap, the Torch produces a sound field extremely similar in severity to that of the Surefire SOCOM556-RC2 on the standard MK18. With its vented end cap, the Torch’s signature severity is very similar to that of the HUXWRX (OSS) HX-QD 556 on the MK18. It is important to note that severity comparisons are valid in the free field. Further research is being conducted on the efficacy of different high flow system technologies and the respective hazards produced near reflecting surfaces.
The LPM Torch uses a vented blast baffle with an oversized primary orifice. The baffles possess annular cavities and are best described as “progressively ported.” With respect to early time gas dynamics, this “nested” blast baffle configuration alters both the shock reflections from primary muzzle blast as well as the gas phase, potentially lowering the impact of the silencer on the kinematics of a host weapon like the the standard MK18 weapon system. This potential may be realized regardless of end cap choice. This purposeful alpha parameter minimization employed by LPM also has the consequence of potentially reducing blast baffle erosion due to the geometry of primary jet impingement. However, it should be noted that muzzle device may significantly play a role in this behavior. The jet expansion from the free orifice in the direct thread mount used in this test should be considered a baseline case. Mount changes may alter the benefits of these early-time gas dynamics.
Although less weapon tuning may be needed with its solid end cap configuration than with other silencers, the vented end cap configuration of the Torch provides superior reduction of ejection port blast hazard to the weapon operator with this silencer.
The rear mount threading of the LPM Torch is 1.375”-24tpi; relatively common in many modern rifle silencers. As a result of this common modular interface, a plethora of mounting systems may be used. The performance of the Torch may be influenced by mounting system choice. The user’s choice of mount may balance system weight, length, durability, utility, and even back pressure of the silencer. The data presented by PEW Science in this Sound Signature Review was measured with the direct thread mount with both tested configurations of the silencer.
In this review, the Liberty Precision Machine Torch 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.
