SSS.6.239 - Liberty Precision Machine Torch 762 and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)
/Liberty Precision Machine Torch 762 on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The Torch 762 is designed and manufactured by Liberty Precision Machine. It is a .30 caliber (7.62mm) centerfire rifle silencer, able to suppress most cartridges appropriately sized to travel through the bore, with fully automatic fire. The silencer is optimized for “small frame” reciprocating rifles though can be used across host size ranges and also with subsonic 300 BLK. It has a 1.74-in diameter and is 6.9 inches long with no mount installed. The rear of the silencer is threaded 1.375-24tpi to accommodate “HUB” compatible mounting systems. The Torch 762 was evaluated with several different mount systems in this test program; with the Baby Bell muzzle brake in the Rearden Atlas HUB coupler, the total system length is 7.47-in, as tested. The silencer core is welded to the first expansion (blast) chamber and is 3D printed Inconel 718 alloy. Without a mount system installed, the silencer weighs 18.6 ounces and the Baby Bell and Rearden Atlas together weigh 2.9 ounces, for a total system weight of 21.5 ounces, as tested. The Torch 762 can be obtained from Silencer Shop.
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 8.1.36 for further details. The PEW-SOFT HD Blast Hazard Prediction Tool and Hazard Mapper is presented in Report 8.1.1.
Liberty Precision Machine Torch 762 10.3-in MK18 AR-15 Free Field Hazard Map Produced by PEW-SOFT HD Blast Hazard Prediction Tool using PEW Science Test Data
Mount System and Barrel Length Performance Notes:
PEW Science evaluated the HUB compatible Torch 762 silencer test specimen in this program on multiple weapon systems with the following mounting systems and the Rearden Atlas GEN 2 HUB mount coupler, as applicable:
Direct-Thread
LPM Liberty Bell Muzzle Brake
LPM Baby Bell Muzzle Brake (test results and analysis documented in this report)
LPM Eclipse Flash Hider
On the 10.3-in standard untuned MK18 automatic rifle, the gross suppression performance of the Torch 762 is the highest with the Baby Bell mount. Performance “losses” with the other mounting systems are measurable but relatively nominal in that they do not appreciably change personnel risk metrics as quantified by the Suppression Rating Damage Risk Criterion (DRC). The largest performance disparity was observed between the Baby Bell and Liberty Bell mounting systems with this silencer on the MK18, and even in that case, the performance differential between the two mounts spans less than half a Suppression Rating category.
With longer 5.56 NATO barrels (14.5-in standard untuned M4A1 automatic rifle, for example) similar trends are observed, though the examination was not as exhaustive. The performance of the Torch 762 is observed to be relatively insensitive to pressure input, in that increasing the barrel length from 10.3-in to 14.5-in does not appear to appreciably influence the Suppression Rating calculations adjacent to the muzzle.
Note that the above mount system and barrel length performance factors are specific to the Torch 762 silencer. In general, mount and barrel length performance variances are silencer specific and should not be extrapolated to other silencer designs.
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-LPM-167-001-26. Therefore, data pertaining to the Torch 762 in this Sound Signature Review is published with the express written permission of Liberty Precision Machine, LLC.
The testing and analysis presented in this Sound Signature Review is of the Liberty Precision Machine Torch 762 mounted with the Baby Bell muzzle brake 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.
Report Table of Contents:
Section 6.239.1 contains a LPM Torch 762 performance summary comparison with other silencers that form the extreme ends of the Personnel Risk spectrum on a suppressed 5.56 AR-15 SBR.
Section 6.239.2 contains LPM Torch 762 test results and analysis on the standard untuned MK18 with the Baby Bell muzzle device connected to the silencer with a Rearden Atlas HUB mount coupler.
Section 6.239.3 contains overall Suppression Rating comparisons of the LPM Torch 762 with dedicated 223 and 30 caliber silencers on the current market, including the Blackbird F556, Otter Creek Labs Infinity 556K, Rampart Range Carson 30, Dead Air Lazarus 6, Otter Creek Labs Universe-36, JK Armament PRO-KOR 556K, Stealth Additive Works Tisha, CAT CACM 556, CAT KK, FOR Systems Monarch Recce, Engaged Industries Operator 5.56, Q Southpaw, Centurion Arms Maximus-L, Otter Creek Labs Infinity, PTR VENT Spiritus 556i, LMT AT ION LT, HUXWRX FLOW 556 Ti, Off Grid Operator Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, Surefire SOCOM556-RC3, Otter Creek Labs Polonium-30, AAC M4-2000 Mod 08, PTR VENT 3, SilencerCo Velos LBP, BOSS Guillotine, CAT WB, 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 6.239.4 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 Liberty Precision Machine Torch 762 mounted with the Baby Bell muzzle brake achieved a composite Suppression Rating™ of 45.2 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.
6.239.1 Liberty Precision Machine Torch 762 Performance Summary and Extreme Ends of Personnel Risk on a Suppressed 5.56 AR-15 SBR
Not all centerfire rifle silencers produce the same suppression performance. Not all silencer technology is created equal.
The suppression performance of a silencer on a given small arm weapon system dictates the following two parameters:
Personnel protection of the operator and bystanders from blast overpressure hazard, both in the free field and near surfaces and in confined spaces. Blast overpressure at amplitudes generated by small arms can harm a human’s inner ears and brain.
Signature detection by adversaries. Muzzle blast is the primary audible source that may be suppressed to mask position.
Historical public research by PEW Science in the Silencer Sound Standard has produced a dataset suitable for examination of technology performance trends, particularly in the case of short barrel reciprocating weapon systems firing the 5.56x45mm NATO intermediate rifle cartridge.
This report presents a third-party laboratory performance evaluation of the Liberty Precision Machine Torch 762 silencer on the standard untuned 10.3-in MK18. The Torch 762 produces performance that places it in the Top 5 MK18 Rankings as of the date of this report publication. It is therefore useful to summarize both the Top 5 performers and Bottom 5 performers, so that the aforementioned performance realities can be easily understood by the reader, contextually. The reader may sort and filter all public Rankings here. Note that the Torch 762 is the highest performing .30 caliber silencer on the 5.56 MK18 tested, to date.
Objectively, the top five performers are the safest for personnel and are likely to mask operator position from adversaries to the greatest degree. Also objectively, the bottom five performers produce the most dangerous environment for personnel and are likely to provide the least concealment of audible signature.
The top five performing systems on the MK18 showcased in public evaluations are:
Liberty Precision Machine Torch 762 (this report)
The bottom five performing systems on the MK18 showcased in public evaluations are:
The performance disparity between the top 5 silencers and bottom five silencers is the result of technological advancement and cartridge specialization driven by public research. All 5 top performers are hybrid designs. Two (the Surefire silencers), and arguably one (the KAC silencer) have hybrid design elements that pre-date the rest of the group. Surefire hybrid technology was derived from early OPS Inc. technology (see here).
The modern hybrid designs provide the greatest performance potentials while balancing operator and bystander protection and weapon system reliability and longevity. Specifically, these types of silencers use early venting and different pressure stages to relieve stagnation and increase suppression efficiency in a given design envelope, while also significantly reducing back pressure. Hybrid designs are not Flow Through silencers, and misclassification is commonplace in the silencer industry; no Flow Through silencers exist other than those manufactured by HUXWRX (formerly OSS). For more details, performance evaluations, and in-depth signature comparisons of hybrid and conventional designs, the reader may examine analysis that is previously published in:
Member Research Supplement 6.103 (supersonic 5.56 NATO)
Member Research Supplement 6.115 (supersonic 7.62 NATO)
Member Research Supplement 6.124 (subsonic 300 BLK)
Member Research Supplement 6.169 (supersonic 5.56 NATO), and recently
Member Research Supplement 6.184 (subsonic 9mm).
To be clear, it is not the addition of a single design element that produces high performance from a small arm weapon system silencer. It is the combination and purposefully engineered integration of multiple design elements that give way to high holistic system performance.
The raw performance of the LPM Torch 762 is illustrated in Figure 1 and Figure 2, below. Figure 1 displays the remainder of the aforementioned top 5 and the bottom 5 performing silencers on the MK18. Figure 2 displays the top 5 and bottom 5 .30 caliber silencers on the 5.56 MK18. The 3D-printed internal structure of the Torch 762 is highly advanced and optimized for small frame gas guns like the 5.56mm MK18, though exhibits relatively high performance on a variety of barrel lengths and cartridge input pressure regimes, to include 7.62 NATO to subsonic 300 BLK. The silencer possesses a high early time flow rate due to significant early venting to its multiple pressure stages. The later pressure stages of the silencer, along with its distal vent array, do help to maintain low back pressure through the entire firing cycle though the back pressure generation on larger volume cartridge such as 7.62 NATO is somewhat higher than with intermediate rifle cartridges like 5.56 NATO. Nonetheless, the “pressure agnostic” performance attributes claimed by Liberty Precision Machine in marketing literature are congruent with the behavior observed in this test program. Topically, a significant observed difference between the Torch 762 and the recently evaluated Blackbird F556 is the lack of external early time jet delay (lack of early external momentum throttle). Along with this more immediate venting behavior, the Torch 762 also produces superior first-round-pop (FRP) control and blast momentum control, in general. This is highly unusual for a .30 caliber silencer on a short barrel 5.56 NATO rifle.
The host weapon system in Figure 1 and Figure 2 is kept constant, and metrics shown are in terms of PEW Science Suppression Rating, which is a human risk metric calculated from raw free field blast overpressure test data. The calculated risk metrics for the unsuppressed case are also presented.
Figure 1. Suppression Rating Comparisons of the Top 5 Safest and Most Dangerous rifle silencers Using PEW-SOFT 5.56x45mm Supersonic MK18 Test Data and PEW Science Analysis
Figure 2. Suppression Rating Comparisons of the Top 5 Safest and Most Dangerous .30 Caliber rifle silencers Using PEW-SOFT 5.56x45mm Supersonic MK18 Test Data and PEW Science Analysis
From the above data, two primary conclusions are apparent:
Silencer over-bore, in general, may reduce suppression performance, but advanced technology can significantly reduce performance losses. Both Surefire silencers and the Rugged silencer are 7.62 weapon system silencers that found historical popular and industry-recommended use on 5.56 weapon systems. The Energetic Armament silencer was purposely over-bored in an effort to reduce baffle erosion under heavy firing schedules. The KAC silencer is not significantly over-bored, but is relatively primitive in its design and its technology is not appropriate to produce high performance in the given system length envelope. The Torch 762 has similar over-bore to the other 7.62mm silencers listed in Figure 1 and Figure 2 but produces significantly higher performance, outperforming most dedicated bore 5.56mm silencers. This is highly unusual and may represent the most advanced 7.62 bore 5.56 NATO suppression performance evaluated in the research, to date.
Rifle silencer suppression technology continues to advance at a rapid pace. The Stealth Additive Works, CAT SURGE BYPASS, and PTR PIP technologies are all extremely advanced. The Infinity technology in the Carson 556 gives way to another advanced hybrid design. The Staged Pressure Vectoring technology in the Blackbird F556 shares some similarities with other hybrid designs in that it possesses early-time venting and lengthened annular flow paths. The Torch 762 is also a hybrid design and uses an LPM technology named Rapid Jet Diffusion to manage flow through early venting and expedient re-routing to multiple pressure stages. In general, all of these systems and technologies are optimized and produced with advanced manufacturing.
Additive manufacturing is required in order to implement the engineering solutions present in many of the most advanced silencers. However, it is not only purposeful design and advanced manufacturing that can contribute to high performance for the end user. Some designs perform better than others, even in the same size classes; there are clear behavioral differences that are showcased with real measured test data and engineering analysis. The performance differentials may be nontrivial, even between new technologies released today. The above metrics are calculated from test data generated on a standard untuned host; weapon system tuning may raise performance potentials, as has been demonstrated in previous public research.
Detailed Torch 762 test data and analysis follows.
6.239.2 Liberty Precision Machine Torch 762 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the LPM Torch 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 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. Liberty Precision Machine Torch 762 Sound Metric Summary
6.239.2.1 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 762 are shown in Figure 3a. The sound signatures of Shot 1 and Shot 2 are shown in Figure 3b, in early time. The real sound impulse (momentum transfer potential) histories from the same 6-shot test are shown in Figure 4a. In Figure 4b, a shorter timescale is shown comparing the impulse of Shot 1 to that of Shots 2 and 3.
Fig 3a. Liberty Precision Machine Torch 762 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 3b. Liberty Precision Machine Torch 762 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 4a. Liberty Precision Machine Torch 762 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 4b. Liberty Precision Machine Torch 762 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The Liberty Precision Machine Torch 762 is a .30 caliber rifle silencer that produces performance on 5.56 NATO weapons that is higher than most dedicated bore 5.56 silencers. The hybrid technology in the Torch 762 is highly advanced and as described in the first section of this report, is highly unusual for a .30 caliber silencer on a short barrel 5.56 NATO rifle.
PEW Science Research Note 1: LPM named the technology in the Torch 762 Rapid Jet Diffusion. In implementation, the silencer has been engineered to provide an extremely high early time flow rate through numerous vent channels beginning around the throat of the first reflector (blast baffle) which load successive vent pathways and form the initial pressure stage of the silencer. Through the pressure stages, the internal flow rate of the Torch 762 is throttled. LPM performed parametric design iterations to optimize this internal flow throttle such that optimum performance was achieved with medium duration, high pressure combustion, characteristic of the 5.56 NATO cartridge from popular barrel lengths. As such, the following performance traits observed in both PEW Science testing and internal LPM evaluations result:
Blast loads clear off of the first reflector out of the first expansion chamber (blast chamber) relatively quickly and this, in conjunction with the silencer’s over-bore (.30 caliber), helps mitigate “gas stacking” during rapid fire on 5.56 weapons. This reduction in blast chamber impulse accumulation is achieved without increasing FRP severity. FRP from the silencer is effectively masked.
The behavior in (1) occurs on both 10.3-in and 14.5-in 5.56 barrels with almost identical suppressed blast severity as quantified by the calculated Suppression Ratings from the measured raw blast overpressure data. While the personnel risk does not decrease when lengthening the barrel and reducing blast pressure input into the silencer, it also does not increase.
FRP control in the high pressure regime is robust, as described above; it is also robust with low pressure input, as evaluated with subsonic 300 BLK. This is relatively unusual given the early time flow rate from the silencer, though is not unprecedented. The significantly controlled late time flow rate heavily contributes to this performance factor.
Congruent with the aforementioned controlled late time flow rate, increasing combustion volume, or duration (moving from 5.56 NATO to 7.62 NATO input, for example) results in the silencer maintaining suppression efficiency, which is notable. However, back pressure does increase. PEW Science has also evaluated the Torch 762 on both 20-in bolt-action rifle and 14.5-in SR-25 reciprocating rifle, both with the 7.62 NATO cartridge, and pure suppression performance scales just as it does with 5.56 NATO, albeit with somewhat higher back pressure. It is important to note that the back pressure of the Torch 762 with 7.62 NATO weapons may still be considered low relative to many 30 caliber silencers. The difference is that the silencer has been optimized for intermediate cartridge combustion volume rather than full size rifle cartridge volume. As a result, it is possible that somewhat more weapon tuning may be needed on 7.62 NATO weapons compared to on 5.56 NATO weapons with the Torch 762, all other things equal.
All of the above observations, together, indicate that the “pressure agnostic” performance of the Torch 762 described in Liberty Precision Machine marketing copy and literature has a high degree of merit. PEW Science testing and analysis of Torch 762 behavior has not revealed any behaviors inconsistent with that performance description.
Future report publications will detail the performance in other combustion regimes. The subject of this report is short barrel 5.56 NATO performance, and demonstrates the most extreme example of performance optimization from the silencer. The average personnel risk field is very balanced for a suppressed 10.3-in MK18 system, as illustrated in the Hazard Map at the beginning of this report and in Silencer Hazard Map Brief 8.1.36. Again, this is highly unusual for a .30 caliber silencer on this weapon system. The jet stability index used to model the forward field in the map, as derived from the measured and calculated Omega Metric, represents late time distal flow rate and is highly controlled. This measured performance attribute, along with the high early time flow rate characteristics described in the above list of performance traits, contributes significantly to the high performance of the silencer while placing operator risk (shooter’s ear Suppression Rating) near the cusp of what remains possible on standard untuned rifles. A shooter’s ear Suppression Rating near 30 on an untuned MK18 or M4 rifle may be considered a “limit” for all practical purposes, in accordance with the research to date.
PEW Science Research Note 2: Viewing the raw measured blast overpressure and impulse data presented above may result in reader confusion; it is not typical for an over-bored .30 caliber silencer to produce these types of signatures on a 10.3-in barrel 5.56 NATO weapon. If one were to view these signatures without labels or context, they may be misinterpreted to be those from a 5.56 bore silencer, or a very long over-bored silencer with high back pressure. They are neither. The following observations are noted:
Very low and controlled amplitude overpressure with moderately long blowdown duration followed by somewhat delayed late-time bolt carrier group (BCG) return to battery (Fig. 3a).
Typical controlled initial coupled jetting followed by a very short delay to primary jet onset (Fig. 3b).
FRP divergence begins from primary jet onset but is highly controlled. Accumulation rate is throttled, plateaus with a rate change prior to peak, and does not significantly differ in severity from any subsequent shots. FRP is effectively masked (Fig. 3b and Fig. 4).
Shots post-FRP are highly controlled and consistent with each other; no early heat-effects are observed (Fig. 4)
In the context of a .30 caliber rifle silencer being used on a 5.56 weapon, observations (1), (3), and (4) are highly unusual. Over-bore typically results in drastically inconsistent and severe blast overpressure and momentum deviations. Historical and pervasive high profile examples of this 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 Dead Air Sandman-S (6.92). Eventually, as silencer technology advanced, silencers like the CAT ODB (6.120) demonstrated in 2023 that over-bore silencer performance could be very competitive with and even eclipse the performance of dedicated bore 5.56 silencers on short barrel rifles. The LPM Torch 762 significantly outperforms the CAT ODB in 5.56 NATO suppression, which represents a notable step forward in over-bore silencer performance in this combustion regime.
In the context of any rifle silencers being used to suppress any barrel length 5.56 weapon, the LPM Torch 762 provides equally significant performance gains, objectively. A very recent example in the research is that of the Blackbird F556 (6.237). Topically, a significant observed difference between the Torch 762 and the F556 is the lack of external early time jet delay (lack of early external momentum throttle) which may indicate a more robust early time flow rate. Along with this more immediate venting behavior, the Torch 762 also produces superior FRP control and blast momentum control, in general. This is highly unusual for a .30 caliber silencer on a short barrel 5.56 NATO rifle.
The LPM Torch 762 is, essentially, a rifle silencer that can be used across cartridge diameter and pressure regimes without concern for significant FRP or performance inconsistency. The main caveat remains regarding some back pressure differences with increased combustion duration (see Research Note 1, sub note 4). Another important caveat is that the Torch 762 is larger than most 5.56 silencers.
PEW Science Research Note 3: At the time of writing, the measured performance of the LPM Torch 762 places it solidly in the top 5 of the overall MK18 PEW Science Rankings, close to the Stealth Additive Works Tisha (6.209) but with a .30 caliber bore sizing which is again, extremely notable. The Torch 762 is 7.47-in long as tested, which also may be a significant attribute for the user, depending on fielding requirements. Nonetheless, its pure suppression performance, low back pressure, high degree of FRP control, and shot to shot consistency, rival that of any of the top performing silencers in this category. For a .30 caliber silencer, it outperforms any other over-bored silencer suppressing 5.56 NATO in the research, to date, and most dedicated 5.56 silencers. For example, even when adapting a dedicated 5.56 bore end cap, the full size Otter Creek Labs Infinity (6.179) is outperformed by the Torch 762 in both pure suppression and back pressure reduction. For further context regarding performance and size balance, the reader is encouraged to use the Suppression Rating Parametric Visualization Tool (Members Only) for independent study.
PEW Science Research Note 4: It is extremely important for the reader to understand the Suppression Ratings are computed with free field test data, and are therefore universal when translating the weapon and operator to different environments without reflections. However, when the environment becomes complex with many reflecting surfaces, performance translation of different systems is not yet possible; sound field shapes and particle velocities result in varied blast wave time-of-arrivals, as well as changes of blast load angles of incidence; these variations change amplitude and phase waveform components. As a result of these inevitable environmental complexities, user impressions will vary, as both the shooter and bystander. Nonetheless, hazard reduction efficacy in the free field, as characterized by the Suppression Rating, holds. The Suppression Rating comparisons are the current state-of-the-art, and the most “apples to apples” sound suppression performance comparisons that currently exist. Further research is ongoing. The reader should note that shooting an LPM Torch 762 indoors and a HUXWRX FLOW silencer indoors may result in different blast overpressure risk profiles.
PEW Science Research Note 5: As in all semiautomatic AR-15 weapon testing, a second pressure pulse originates from the ejection-port signature of the weapon and it occurs early enough in time such that its waves coalesce with that of the muzzle signature. However, in late time (at approximately 95 ms in Figure 3a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 does not display this event due to the bolt remaining open after the sixth and final round is fired from the magazine.
PEW Science Research Note 6: The closing time of the AR-15 bolt is directly related to the flow restriction of a silencer for a given weapon system. PEW Science has determined bolt closing time variation from the unsuppressed state to be a reliable indicator of silencer back pressure, with strong correlation with the PEW Science Back Pressure Metric, Omega and the alpha parameter. However, PEW Science has also determined that the indicator is unreliable upon upper receiver fouling. Sound signatures are not influenced by this fouling, as these kinematics occur in late time, after gas venting to atmosphere. Momentum transfer, weapon condition (upper receiver fouling), and other factors, can significantly influence bolt closing time. PEW Science urges the reader to exercise extreme caution if using the published bolt closing time to make determinations regarding silencer flow restriction (back pressure) or weapon system kinematics. This type of calculation may provide erroneous results, as the weapon condition at the time of each test is not published data. The time-scale duration showing bolt closing time is only published by PEW Science such that the signature data pedigree may be verified.
The shape, timing, and magnitudes of the early-time pressure pulses and overall shape of the impulse waveforms measured at the muzzle, from shot-to-shot, are relatively consistent. The consistency of the waveform amplitudes highlight the silencer’s overall sound performance consistency at the muzzle after the FRP, as well as the relative consistency of the tested automatic rifle firearm configuration.
As typically indicated, first-round sound signatures always differ from subsequent shots, as the atmosphere within the silencer changes. The FRP phenomenon cannot always be shown by viewing only the peak sound pressure. This is one of the reasons why The Silencer Sound Standard requires examining multiple sound signature metrics. Ammunition consistency can play a role in the determination of FRP, however, the close examination of measured pressure and impulse waveforms typically excludes ammunition from the possible factors influencing true FRP, due to the relative consistency of most high quality factory ammunition.
PEW Science Research Note 7: Note that the muzzle Suppression Rating of the LPM Torch 762 is 44.9 and the at-ear Suppression Rating is 30.7; different zones on the Suppression Rating Dose Chart, but both higher than typical on this weapon system. The lower back pressure of the Torch 762, along with its strong average muzzle suppression, contributes to a less severe ejection port blast signature, which further decreases shooter hazard on the standard MK18 weapon system. The reader is encouraged to examine the Silencer Hazard Map at the top of this report as detailed in Silencer Hazard Map Brief 8.1.36. Weapon tuning will influence hazard reduction efficacy, and is outside the scope of this study.
The signatures measured at the shooter’s ear are presented and analyzed in the full Member Version of this report.
Comprehensive MK18 performance comparisons are presented below.
6.239.3 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 7 presents a comparison of the PEW Science Suppression Rating of the Torch 762 with that of several other silencers on the MK18 weapon system. The standard PEW Science MK18 test host weapon system is described in Public Research Supplement 6.51.
Figure 7. Suppression Rating Comparisons of the Liberty Precision Machine Torch 762 and other rifle silencers, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 7 presents an overall summary of the postulated hazards to the operator and bystanders when fielding a variety of different silencers on the standard MK18 weapon system. The Liberty Precision Machine Torch 762 from this test program is shown in red. Hazards are expressed with the Suppression Rating; a holistic parameter that captures human inner ear damage risk potential from a measured impulsive complex blast 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 and Hazard Map 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. Analytically computed metrics are color-coded in the Rankings Table, in all Silencer Hazard Maps, and keyed to the dose chart for user interpretation.
The following gross conclusions can be made from the metrics presented in Figure 7, above:
The LPM Torch 762 produces free field bystander hazard reduction on par with the following silencers on the MK18 weapon system:
The free field operator (shooter) hazard reduction of the LPM Torch 762 with the standard untuned MK18 weapon system is higher than it is with several other designs due to its higher flow rate (lower back pressure) and its relatively efficient muzzle suppression for its size. The MK18 operator protection with the Torch 762 is on par with or exceeding that of the:
The top five performing systems on the MK18 showcased in public evaluations are:
Liberty Precision Machine Torch 762 (this report)
The bottom five performing systems on the MK18 showcased in public evaluations are:
Note that the Torch 762 is the highest performing .30 caliber silencer on the 5.56 MK18 tested, to date.
PEW Science Research Note 10: Without weapon system tuning, operator hazards from a suppressed MK18, in the free field, plateau at Suppression Ratings near 30. This is due to ejection port blast loads. However, this does not mean that silencers with similar shooter’s ear Suppression Ratings will sound the same to the shooter, in the free field. On the contrary, what an operator hears through the entire time regime of a gun shot event and subsequent environmental reflections, and which acute hazards manifest, may be different. The reader is strongly encouraged to review the published Silencer Hazard Map at the top of this report and in Silencer Hazard Map Brief 8.1.36. Furthermore, to illustrate two extremes, the difference in spatial hazards from a Flow Through silencer and a high back pressure silencer are directly compared in Silencer Hazard Map Brief 8.1.5 (HUXWRX FLOW 556k vs. SilencerCo Saker 556).
As stated in Research Note 3, at the time of writing, the measured performance of the LPM Torch 762 places it solidly in the top 5 of the overall MK18 PEW Science Rankings, close to the Stealth Additive Works Tisha (6.209) but with a .30 caliber bore sizing which is again, extremely notable. The Torch 762 is 7.47-in long as tested, which also may be a significant attribute for the user, depending on fielding requirements. Nonetheless, its pure suppression performance, low back pressure, high degree of FRP control, and shot to shot consistency, rival that of any of the top performing silencers in this category. For a .30 caliber silencer, it outperforms any other over-bored silencer suppressing 5.56 NATO in the research, to date, and most dedicated 5.56 silencers. For example, even when adapting a dedicated 5.56 bore end cap, the full size Otter Creek Labs Infinity (6.179) is outperformed by the Torch 762 in both pure suppression and back pressure reduction. For further context regarding performance and size balance, the reader is encouraged to use the Suppression Rating Parametric Visualization Tool (Members Only) for independent study.
Hybrid designs continue to demonstrate significant performance with supersonic ammunition suppression, and silencers like the F556, and others, show that performance can be achieved in compact design envelopes. The performance of these next generation systems are significantly elevated when compared to that of highly prolific previous generation hybrids such as the Surefire SOCOM556-RC2 (6.52) and other newly released military silencer hybrids such as the KAC PRT family (6.156) on this weapon system. Users now have additional high performance practical options to reduce weapon system length and maintain hazard reduction.
As detailed in this report, 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 hazard reduction 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.
6.239.4 Review Summary: Liberty Precision Machine Torch 762 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 Liberty Precision Machine Torch 762 mounted with the Baby Bell muzzle brake achieved a composite Suppression Rating™ of 45.2 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 Liberty Precision Machine Torch 762 is a mid-size .30 caliber rifle silencer that provides significantly high suppression performance with a variety of cartridge pressures ranging from subsonic 300 BLK to supersonic 5.56 NATO to 7.62 NATO. The silencer has a high early time flow rate and is optimized to produce significant suppression with low back pressure on small frame reciprocating gas guns with both short and long barrel lengths. The silencer is 3D printed from Inconel alloy, HUB compatible, and approximately 7 inches long without a mount. With its manufacturer-claimed and independently verified “pressure agnostic” behavior, high performance first-round-pop (FRP) suppression, and very high 5.56 suppression performance and consistency even in the over-bore condition, the Torch 762 represents one of the biggest total steps forward in 30 caliber rifle silencer performance in the recent research.
LPM named the technology in the Torch 762 Rapid Jet Diffusion. In implementation, the silencer has been engineered to provide an extremely high early time flow rate through numerous vent channels beginning around the throat of the first reflector (blast baffle) which load successive vent pathways and form the initial pressure stage of the silencer. Through the pressure stages, the internal flow rate of the Torch 762 is throttled. LPM performed parametric design iterations to optimize this internal flow throttle such that optimum performance was achieved with medium duration, high pressure combustion, characteristic of the 5.56 NATO cartridge from popular barrel lengths.
In the context of a .30 caliber rifle silencer being used on a 5.56 weapon, the high performance and consistency observed in this test program are both highly unusual. Over-bore typically results in drastically inconsistent and severe blast overpressure and momentum deviations. Historical and pervasive high profile examples of this may be examined in test reports featuring products such as the Rugged Razor762, the Energetic Armament ARX, the Rugged Razor556, the Q Trash Panda, and the Dead Air Sandman-S. Eventually, as silencer technology advanced, silencers like the CAT ODB demonstrated in 2023 that over-bore silencer performance could be very competitive with and even eclipse the performance of dedicated bore 5.56 silencers on short barrel rifles. The LPM Torch 762 significantly outperforms the CAT ODB in 5.56 NATO suppression, which represents a notable step forward in over-bore silencer performance in this combustion regime.
In the context of any rifle silencers being used to suppress any barrel length 5.56 weapon, the LPM Torch 762 provides equally significant performance gains, objectively. A very recent example in the research is that of the Blackbird F556. Topically, a significant observed difference between the Torch 762 and the F556 is the lack of external early time jet delay (lack of early external momentum throttle) which may indicate a more robust early time flow rate. Along with this more immediate venting behavior, the Torch 762 also produces superior FRP control and blast momentum control, in general. This is highly unusual for a .30 caliber silencer on a short barrel 5.56 NATO rifle. The LPM Torch 762 is, essentially, a rifle silencer that can be used across cartridge diameter and pressure regimes without concern for significant FRP or performance inconsistency. The main caveat remains regarding some back pressure differences with increased combustion duration (see Research Note 1, sub note 4). Another important caveat is that the Torch 762 is larger than most 5.56 silencers.
At the time of writing, the measured performance of the LPM Torch 762 places it solidly in the top 5 of the overall MK18 PEW Science Rankings, close to the Stealth Additive Works Tisha but with a .30 caliber bore sizing which is again, extremely notable. The Torch 762 is 7.47-in long as tested, which also may be a significant attribute for the user, depending on fielding requirements. Nonetheless, its pure suppression performance, low back pressure, high degree of FRP control, and shot to shot consistency, rival that of any of the top performing silencers in this category. For a .30 caliber silencer, it outperforms any other over-bored silencer suppressing 5.56 NATO in the research, to date, and most dedicated 5.56 silencers. For example, even when adapting a dedicated 5.56 bore end cap, the full size Otter Creek Labs Infinity is outperformed by the Torch 762 in both pure suppression and back pressure reduction. For further context regarding performance and size balance, the reader is encouraged to use the Suppression Rating Parametric Visualization Tool (Members Only) for independent study.
The Torch 762 is approximately 7 inches long without a mount. The tested HUB coupler and muzzle brake increased the effective system length to approximately 7.5 inches. Performance with other mount types does differ in both signature suppression and back pressure; the potential performance differentials discovered in this test program resulted in less than half a Suppression Rating category of performance variation.
The tested silencer is 3D printed Inconel alloy and is expected to offer requisite durability and longevity for aggressive firing schedules. PEW Science has not evaluated the durability of this silencer. As always, the user should remain cognizant of their personal firing schedules. The user should contact Liberty Precision Machine to ensure compatibility for their use case.
In this review, the Liberty Precision Machine Torch 762 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.
