SSS.6.183 - BOE Mod 1 and the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle
/BOE Mod 1 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
The Mod 1 is designed and manufactured by BOE; a division of C Products Defense. It is a multi-core centerfire rifle silencer. In the configuration tested with the 5.56 core installed, it is intended to suppress the 5.56x45mm cartridge with semiautomatic or fully automatic fire. The Mod 1 has a 1.75-inch diameter and is 6.8 inches long without a mount. The silencer may be attached to a variety of weapon systems depending on the user’s choice of mount; the BOE Quick Disconnect Adapter with the dual taper 1/2-28tpi Muzzle Brake QD mount installed increases the system length to 7.7 inches. Other mounting options are possible due to the rear of the silencer body being HUB compatible (1.375”-24 tpi threading). The outer tube of the Mod 1 is constructed of titanium, whereas the silencer core may be 3D printed titanium or Inconel alloy, depending on the user’s choice. The end cap and core is removable from the outer tube. Both solid and vented end caps are available. The silencer body and Inconel core together weigh 20.6 ounces without a mount. With the BOE mounting system installed, the total system weight increases to 26.1 ounces, as tested. The Mod 1 can be obtained from BOE Suppression.
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-CPD-085-001-24. Therefore, data pertaining to the Mod 1 in this Sound Signature Review is published with the express written permission of C Products Defense, Inc.
System Evaluation Note: The BOE Mod 1 silencer accepts both solid and vented end caps. This test report examines the performance of the silencer with the solid end cap installed. Vented end cap evaluation is forthcoming.
The testing and analysis presented in this Sound Signature Review are of the BOE Mod 1 on the M4A1 Mid-Gas Automatic AR15 rifle, chambered in 5.56x45mm NATO with a 14.5-inch barrel. Federal XM193 55gr ammunition was used in the tests. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127.
Section 6.183.1 contains Mod 1 test results and analysis.
Section 6.183.2 contains overall gross Suppression Rating comparisons of the BOE Mod 1 with other rifle silencers on the current market on the M4A1 Mid-Gas Rifle, including various configurations of the Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, CAT/WB/A1, and Surefire SOCOM556-RC2.
Section 6.183.3 contains an article summary and PEW Science laboratory staff opinions.
Summary: When paired with the 14.5-in barrel M4A1 and fired with Federal XM193 with the muzzle brake QD mount, the BOE Mod 1 with the solid end cap achieved a composite Suppression Rating™ of 44.1 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
6.183.1 BOE Mod 1 Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the BOE Mod 1 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. BOE Mod 1 Sound Metric Summary
6.183.1.1 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 BOE Mod 1 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. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature
Figure 2a. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
The BOE Mod 1 is a full-size rifle silencer with a modular monocore design. The traditional outer tube houses an interchangeable 3D-printed monocore that may vary in both material and cartridge designation. The test specimen evaluated in this report was configured with the Inconel 5.56 core. Other cores are available in 30, 36, and 46 caliber sizes. All are titanium, with the exception of the Inconel variants available in 5.56 and 30 caliber. Solid and vented end caps are also available.
PEW Science Technology Note: The core design of the BOE Mod 1 uses traditional baffle cone geometry, in a gross sense. However, the core is relatively unique in that all baffles other than the final distal baffle possess alternating radially angular surfaces that terminate longitudinally into an outer coarse lattice. This lattice forms the outer diameter boundary of the core. The longitudinal termination of each cone “ridge” forms the outer lattice wall. When the core is installed in the outer tube, its outer diameter does not touch the inner diameter of the tube. Therefore, there is annular space between the core and tube. The geometry is best viewed in photographs on the manufacturer’s website. Commonality of this geometry is present in all current caliber core designations, with the following design features of note being relevant to performance:
The radially alternating angular blast baffle and subsequent baffles are not ported.
The final distal cone baffle is radially ported.
The lattice wall “pockets” in the first expansion (blast) chamber present the same blast load angle of incidence as the pockets in each subsequent expansion chamber between baffles; the subsequent chambers being formed by the termination of the baffle ridges.
The system suppression performance is dependent upon maximizing surface area contact with geometry described in (1) and (3). The system back pressure reduction performance is dependent upon the same, in addition to annular flow, the porting in (2), and end cap selection by the user.
PEW Science Research Note 1: The blast overpressure in the free field, measured 1.0 m left of the silencer’s end cap, indicates typical blowdown behavior with significantly suppressed blast pressure amplitude in the time regime following initial jetting. There are significant first-round-pop (FRP) combustion propagation indicators in both pressure space (Fig. 1) and impulse space (Fig. 2). Technical performance observations include:
Significant FRP jetting after initial coupled exit and prior to peak primary FRP (Fig. 1a).
Significant FRP rarefaction onset prior to normalized flow (Fig. 1a).
Expedient increase to peak FRP positive phase impulse without step change(s) prior to maximum (Fig. 2b).
Relatively consistent post-FRP blast load impulse accumulation throughout the time regime of primary blowdown (Fig. 2a).
The FRP ancillary blast load propagation observed in the above test measurements likely indicates significant annular utilization. This postulation is made based upon the significant amount of core surface area contact described in the preceding Technology Note. However, as shown in the gross system shooter’s ear (operator) Suppression Rating, the BOE Mod 1 with its solid end cap may not significantly reduce adverse ejection port blast propagation from the weapon system. This leads to the further postulation that early-time internal blast load impulse accumulation is occurring from the non-ported blast baffle, the outer lattice angled pockets and tube wall, and potentially even from the muzzle brake mount. Internal PEW Science testing of this system on other platforms suggests that mount may influence system back pressure. Additionally, end cap venting does reduce the system Omega Metric, at the cost of decreased muzzle (bystander) Suppression Rating.
PEW Science Research Note 2: Due to the lattice pockets forming vents to the annular cavity created by the core and tube wall, the BOE Mod 1 is classified as a hybrid design in the PEW Science research taxonomy. This classification is given despite the aforementioned increased back pressure characteristics in the present configuration. It should be noted that efficacy of implementation does not preclude existence of design features.
PEW Science Research Note 3: With regard to overall suppression performance, the design attributes discussed above result in significant overall muzzle blast load propagation suppression performance, and that is reflected in the relatively high muzzle (bystander) Suppression Rating of the BOE Mod 1. With a muzzle Suppression Rating of 44.0, the Mod 1 provides bystander protection 1.0 m left of the muzzle that is equal to that of the PTR VENT Spiritus 556i (6.176) on the PEW Science standard M4A1 weapon system. The BOE Mod 1 is over an inch longer than the VENT Spiritus 556i; this highlights the relative efficiencies of both technologies; the coarse lattice and core interface of the hybrid Mod 1, and the Purposely Induced Porosity (PIP) variable lattice and blast load routing of the hybrid Spiritus. Both hybrid designs, they manage internal blast load propagation and heat transfer in different ways. System back pressure in each system is extremely different, as shown in the shooter’s ear Suppression Ratings displayed in Figure 5 in Section 6.183.2 of this report.
PEW Science Research Note 4: In the PEW Science Research taxonomy, hybrid design silencers are those in which elements of both conventional and high flow rate silencers are used, coupled with other technology variations and staged elements to provide parametrically varied performance attributes. Such attributes include the ability to reduce impulse accumulation from early-time shock reflections while significantly altering the rate of proximal and distal venting. These silencers may allow for minimal reciprocating weapon functional influence, while at the same time significantly suppressing signature to the operator and bystanders. Hybrid designs span a large range of the market in both brand and performance in different combustion regimes. There also exist subcategories of this class of silencers that have been shown to demonstrate efficacy in multiple flow regimes. Discussion of these subcategories is outside the scope of this report. Other hybrid designs and staged hybrids include those from Centurion Arms, PTR, CAT, CGS, SilencerCo, Surefire, updated recent Dead Air and Otter Creek Labs models, and others. For an overview of the three primary classes of rifle silencer designs, the reader is encouraged to review PEW Science Research Supplement 6.169.
PEW Science Research Note 5: 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 85 ms in Figure 1a) the mechanical noise of the bolt closing is observed. The pressure signature of Shot 6 does not display this event due to the bolt remaining open after the sixth and final round is fired from the magazine.
PEW Science Research Note 6: The closing time of the AR15 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 BOE Mod 1 with its solid end cap is 44.0 and the at-ear Suppression Rating is 19.7; different zones on the Suppression Rating Dose Chart. In the test solid end cap configuration, with the tested mount, the back pressure of the BOE system does contribute to elevated ejection port blast operator hazard. In this configuration, the back pressure is not low enough to reduce the ejection port blast loads to the shooter as significantly as some other hybrid design silencers on the standard M4A1 weapon system.
The signatures measured and analyzed at the shooter’s ear are presented below.
6.183.1.2 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. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature
Figure 3b. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Pressure Signature, Short Time Window
Figure 4a. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature
Figure 4b. BOE Mod 1 5.56x45mm NATO M4A1 Automatic Rifle Ear Sound Impulse Signature Peaks
Note the shape of the blast overpressure signature measured 6 inches right of the shooter’s right ear in Figure 3a. The reader is encouraged to compare this behavior of the BOE Mod 1 system it with that of the signature in the same figure shown in the PTR VENT Spiritus report, on the same weapon system.
PEW Science Research Note 8: After muzzle blast load blowdown out of the silencer, silencer systems exhibiting significantly low back pressure typically display low pressure amplitudes on reciprocating systems like the M4 rifle. The BOE Mod 1 on this weapon system is inducing ejection port blast loads that are coalescing with latent muzzle blast. However, because its muzzle suppression is so extreme, and the back pressure is also not extreme, the net impulse accumulation presents as relatively typical. There is no FRP front-loading to the impulse histories as seen in typical hybrids, but there is also not significant late time positive phase accumulation. For the so-called “over gassed” M4 host, the operator hazard from the BOE Mod 1 is not severe relative to other models, but it is elevated. As noted in the preceding section of this report, the vented end cap does lower the silencers Omega Metric, dropping back pressure, and reducing some ejection port blast hazard. As typical, the reader may reference Section 6.111.3 in Report 6.111 for a case study in which relative FRP blast load momentum accumulation timing is used to discern overall ejection port blast load coalescence behavior.
PEW Science Research Note 9: The muzzle blast FRP severity to bystanders with the BOE Mod 1 on this weapon system is approximately twice as severe as subsequent shots, on average. But to the shooter, the FRP severity is only approximately 50% more severe as subsequent shots with this silencer on this weapon system. This relative severity differential results from the contribution of ejection port blast hazards to shooter risk. Bystanders 1.0 m left of the end cap of the silencer are not subjected to ejection port blast hazards nearly to the same degree as the operator of the weapon system.
PEW Science Research Note 10: It is likely that the Daniel Defense M4A1RIII weapon system, as fielded, is “over-gassed”. Although this type of weapon parameter trait can increase reliability of the system in adverse conditions (e.g. lacking lubrication, use of weaker ammunition, debris inference in the reciprocating system, etc.) it is undesirable from a pure blast overpressure hazard reduction standpoint, to the weapon operator. The primary benefit of high flow rate rifle silencers (PTR VENT series, HUXWRX Flow-Through FLOW series, CAT Surge Bypass silencers, etc) is being able to maintain unsuppressed system behavior while suppressed; this allows for less modification to the systems, high reliability, and less user-error when fielding. However, when a system is already “over-gassed,” less hazard reduction may be noted. The BOE Mod 1 may still be able to provide excellent ejection port blast hazard reduction on this weapon system, but it may require the vented end cap be installed and/or the gas port size of the weapon be reduced. As it stands, the over-gassed host result in a net shooter’s ear Suppression Rating that is lower than that of other high performance high flow rate silencers.
With regard to holistic sound field, especially near reflecting surfaces, the exceptional muzzle Suppression Rating of the BOE Mod 1 likely to provide highly positive operator experience in a variety of environments. Any degree of M4A1RIII weapon system tuning (heavier buffer, smaller gas port orifice, etc) is likely to result in higher performance with regard to operator blast load protection.
Like the recently evaluated Echo Zulu Defense X1R556-Ti, the BOE Mod 1 may be considered to present a less “balanced” shooter’s ear signature on this weapon system than some other high flow rate designs.
Gross hazards and behaviors with the M4A1 weapon system are compared in the following section.
6.183.2 Suppression Rating Comparison (5.56x45mm from the M4A1)
Figure 5 presents a comparison of the PEW Science Suppression Ratings of the BOE Mod 1 in the solid end cap configuration with that of other rifle silencers on the M4A1 weapon system. The standard PEW Science M4A1 test host weapon system is described in Public Research Supplement 6.127. As PEW Science research with the M4A1 system continues, the dataset will be further populated.
Figure 5. Suppression Rating Comparisons of the BOE Mod 1 with solid and cap and the Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, HUXWRX FLOW 556 Ti, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, Surefire SOCOM556-MIN2, CAT WB, and SOCOM556-RC2 with different mounts, Using PEW-SOFT 5.56x45mm Supersonic Test Data and PEW Science Analysis
Figure 5 presents an overall summary of the postulated hazards to the operator and bystanders when fielding a BOE Mod 1 with solid end cap on the M4A1 weapon system. Data is also presented for the fielding case of the Echo Zulu Defense X1R556-Ti (6.181), PTR VENT Spiritus 556i (6.176), HUXWRX FLOW 556 Ti (6.168), Surefire SOCOM556-RC2 (6.128), SOCOM556-MINI2 (6.144), and KAC QDC PRT units (6.156) on different muzzle devices, along with fielding of the CAT WB (6.130). Hazards are expressed with the Suppression Rating; a holistic parameter that captures human inner ear damage risk potential from a measured impulsive complex overpressure signature during the entire time regime of weapon operation, including combustion, complete blowdown, and all mechanical operation, including the carrier group returning to battery, in the true free field. The parameter may be used with the dose chart at the beginning of this report. The PEW Science Suppression Rating is a damage risk criterion (DRC), a lower Suppression Rating indicates a higher personnel hazard in the free field - it is not a subjective quantity; it is an objective quantification of hearing damage risk potential. Due to its true free field test data origin and complete waveform analytical calculation basis, it is the only known universal suppressed weapon system signature comparison metric available.
The following gross conclusions can be made from the above:
The BOE Mod 1 achieves significant hazard reduction to bystanders directly adjacent to the weapon system, in the free field, on the standard untuned M4A1RIII weapon system. Its performance in this metric is the highest in the group, matching that of the shorter and smaller diameter PTR VENT Spiritus 556i (6.176). This occurs despite the noticeable bystander FRP from the BOE Mod 1. The large amount of surface area present in the coarse lattice of the core design, along with the annular volumetric expansion chamber and ridged baffles, are largely responsible for its high average muzzle suppression performance.
The free field operator (shooter) hazard reduction with the BOE Mod 1 on the standard untuned M4A1RIII weapon system is less robust than that of other hybrid designs in the dataset. The phenomena responsible for this performance reduction, to include increased early-time back pressure, are discussed in Research Note 1 of this report. The M4A1RIII is a somewhat “over-gassed” rifle. Significant hazard reduction efficacy is extremely difficult to achieve without weapon modification. Furthermore, as discussed with in-depth analysis in previous Member Research Supplement 6.169 on the MK18, specific signature attributes and environmental factors can and will influence user perception and experience. With regard to holistic sound field, especially near reflecting surfaces, the high muzzle Suppression Rating and distal blast momentum control of the BOE Mod 1 are likely to provide highly positive operator experience in a variety of environments, especially with weapon tuning. Any tuning of the M4 system for ejection port blast reduction will result in higher levels of overall operator hazard reduction performance with this silencer. FRP, however, will still influence operator hazard differentials during the first shot. That performance detriment can not be “tuned out” of the system without the use of some type of ablative medium. It should also be noted that mount system may play a role with BOE Mod 1 back pressure; the tested muzzle brake may potentially elevate this parameter.
While some advanced hybrids from Knights Armament such as the KAC QDC PRT Series (6.156) produce balanced signatures, their overall blast pressure hazard reduction is significantly lower than that of some other hybrid designs, including the BOE Mod 1. Users may choose silencers based on favoring certain mounting systems and durability metrics that may preclude the preference of high signature reduction performance. Furthermore, legacy designs such as the Surefire SOCOM556-RC2 with the 3-Prong flash hider still provide relatively high hazard reduction for both the operator and bystanders when compared to several other systems. The RC2 uses a legacy version of Surefire Total Signature Reduction hybrid technology and it does pay dividends with this system. Proper mount use is critical with Surefire rifle silencer systems, in general.
The performance gap between the two extremes of suppressed systems displayed in the current M4A1 dataset is significant; the difference in signature severity produced by the BOE Mod 1, Echo Zulu Defense X1R556-Ti, PTR VENT Spiritus 556i, and CAT WB on this weapon system, compared with that of a WARCOMP-equipped SOCOM556-MINI2, for example, is pronounced. The performance of a MAMS-equipped KAC 556 QDC/MCQ-PRT produces significantly higher blast load hazard to bystanders, but may be on par with the BOE Mod 1 for weapon operator hazard reduction in the free field, depending on mount choice. This conclusion is only valid on standard untuned systems.
Increased gross flow rate (lower back pressure) does pay dividends in ejection port blast hazard reduction to the 14.5-in barrel M4A1 midgas weapon operator, but without weapon modification, shooter’s ear protection levels may plateau. This has now been demonstrated several times with high performance silencers. Management of internal blast load impulse accumulation and flow rate in multiple time regimes is paramount for holistically balanced suppression performance on such weapon systems. The BOE Mod 1 can accept a vented end cap for use, that drops its Omega Metric and lowers late-time back pressure. This can increase the shooter’s ear (operator) Suppression Rating on a given reciprocating weapon system. Evaluation of the efficacy of the vented end cap with this silencer is forthcoming.
As detailed in this report, the Suppression Rating at the shooter’s ear may be significantly influenced by the ejection port signature from an AR15; 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.
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.
6.183.3 Review Summary: BOE Mod 1 on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-in Barrel
When paired with the 14.5-in barrel M4A1 and fired with Federal XM193 with the muzzle brake QD mount, the BOE Mod 1 with the solid end cap achieved a composite Suppression Rating™ of 44.1 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 BOE Mod 1 is a full size multi-core rifle silencer. With its 5.56 core and solid end cap, the Mod 1 exhibits significant overall signature suppression performance, and its back pressure may be reduced with the use of a vented end cap. The outer tube of the BOE Mod 1 system is titanium, and the user may choose silencer cores of both different caliber and different material (Inconel or titanium). The 3D-printed cores are "swappable” by the user, from the manufacturer. Material choice, end cap choice, and core bore size choice will dictate user experience in blast overpressure suppression, depending on weapon system selection. The silencer’s core geometry provides a significant amount of surface area, which is one of factors producing its high muzzle suppression performance.
The core design of the BOE Mod 1 uses traditional baffle cone geometry, in a gross sense. However, the core is relatively unique in that all baffles other than the final distal baffle possess alternating radially angular surfaces that terminate longitudinally into an outer coarse lattice. This lattice forms the outer diameter boundary of the core. The longitudinal termination of each cone “ridge” forms the outer lattice wall. When the core is installed in the outer tube, its outer diameter does not touch the inner diameter of the tube. Therefore, there is annular space between the core and tube. The geometry is best viewed in photographs on the manufacturer’s website. Commonality of this geometry is present in all current caliber core designations.
Due to the lattice pockets forming vents to the annular cavity created by the core and tube wall, the BOE Mod 1 is classified as a hybrid design in the PEW Science research taxonomy. This classification is given despite increased back pressure characteristics in the present configuration. It should be noted that efficacy of implementation does not preclude existence of design features. The BOE Mod 1 can accept a vented end cap for use, that drops its Omega Metric and lowers late-time back pressure. This can increase the shooter’s ear (operator) Suppression Rating on a given reciprocating weapon system. Evaluation of the efficacy of the vented end cap with this silencer is forthcoming.
The BOE Mod 1 achieves significant hazard reduction to bystanders directly adjacent to the weapon system, in the free field, on the standard untuned M4A1RIII weapon system. Its performance in this metric is the highest in the currently evaluated group, matching that of the shorter and smaller diameter PTR VENT Spiritus 556i. This occurs despite the noticeable bystander first-round-pop (FRP) from the BOE Mod 1. The large amount of surface area present in the coarse lattice of the core design, along with the annular volumetric expansion chamber and ridged baffles, are largely responsible for its high average muzzle suppression performance.
With regard to relative performance factors, the muzzle Suppression Rating of the BOE Mod 1 is now in the top 2 of the PEW Science laboratory M4A1 5.56 Rankings. The shooter’s ear Suppression Rating, characterizing operator risk, is in the bottom quartile of Rankings in the dataset of silencer performance on the M4A1RIII. The BOE Mod 1 is 6.8 inches long without a mount.
With regard to durability, BOE Mod 1 will exhibit varying degrees of resilience, depending upon both core material choice and core bore aperture choice. The user is encouraged to contact the manufacturer with questions regarding applicability for their specific use case.
The BOE Mod 1 is HUB mount capable. The user may adapt the silencer to a variety of mounting systems of their preference.
In this review, the BOE Mod 1 performance metrics depend upon suppressing a supersonic centerfire rifle cartridge on a commonly fielded 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.
