SSS.6.175- PTR VENT Spiritus 556i and the MK18 5.56x45mm Short Barrel Automatic AR15 Rifle (Free Version)
/PTR VENT Spiritus 556i on the MK18 5.56x45mm AR15 with 10.3-in Barrel
The VENT Spiritus 556i is designed and manufactured by PTR Industries. It is a 223 caliber centerfire rifle silencer, intended to suppress the 5.56x45mm cartridge with semiautomatic or fully automatic fire. The VENT Spiritus 556i has a 1.62-inch diameter and is 6 inches long. The silencer may be attached to a variety of weapon systems depending on the user’s choice of mount; the included 1/2-28tpi direct thread mount increases the system length to 6.38 inches. Other mounting options are possible due to the rear of the silencer body being HUB compatible (1.375”-24 tpi threading). The entirety of the VENT Spiritus 556i structure is monolithic and constructed from 3D Printed Inconel alloy. The silencer weighs 15.6 ounces and the included direct thread mount weighs 2.1 ounces, for a total system weight of 17.8 ounces, as tested. The VENT Spiritus 556i can be obtained from PTR Dealers.
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-PTR-084-001-24. Therefore, data pertaining to the VENT Spiritus 556i in this Sound Signature Review is published with the express written permission of PTR Industries Inc.
The testing and analysis presented in this Sound Signature Review are of the VENT Spiritus 556i on the MK18 Automatic AR15 rifle 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.
PTR VENT Spiritus 556i testing and analysis on the standard 14.5-in barrel M4A1RIII is documented here.
Section 6.175.1 contains VENT Spiritus 556i test results and analysis.
Section 6.175.2 contains overall Suppression Rating comparisons of the VENT Spiritus 556i with with dedicated 223 and 30 caliber silencers on the current market, including the 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 6.175.3 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 PTR VENT Spiritus 556i with direct-thread mount achieved a composite Suppression Rating™ of 37.5 in PEW Science testing.
When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 44.2 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
6.175.1 PTR VENT Spiritus 556i Sound Signature Test Results
A summary of the principal Silencer Sound Standard performance metrics of the PTR VENT Spiritus 556i 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. PTR VENT Spiritus 556i Sound Metric Summary
6.175.1.1 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 PTR VENT Spiritus 556i 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 Shots 2 and 3.
Fig 1a. PTR VENT Spiritus 556i 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. PTR VENT Spiritus 556i 5.56x45mm NATO MK18 Automatic Rifle Sound Pressure Signature
Figure 2a. PTR VENT Spiritus 556i 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. PTR VENT Spiritus 556i 5.56x45mm NATO MK18 Automatic Rifle Muzzle Sound Impulse Signature
The PTR VENT Spiritus 556i represents a significant update to the VENT series. Like other silencers in the series, the VENT Spiritus 556i is a hybrid design, incorporating both high flow rate features and conventional geometries to control distal blast propagation while reducing adverse influence on weapon function. For an overview of the three primary classes of rifle silencer designs, the reader is encouraged to review PEW Science Research Supplement 6.169.
The design of the VENT Spiritus 556i does share some similarities with that of the previously evaluated PTR VENT 3 (6.135). However, notably, the VENT Spiritus 556i is almost 2 inches shorter than the VENT 3 and constructed of Inconel alloy instead of titanium alloy. Another significant difference between the two silencers is the radial venting present at the distal end of the VENT Spiritus 556i. All PTR VENT silencers utilize Purposely Induced Porosity (PIP) technology both internally and at venting locations, including at the end caps. The VENT Spiritus 556i includes twelve PIP vents around the distal outer circumference.
PEW Science Research Note 1: Multiple flow paths, including annular rerouting, are present in the VENT Spiritus 556i. As a staged design, the silencer does allow for high pressure blast load to propagate through multiple areas of the silencer simultaneously, and a significant flow path terminates at the distal radial PIP vents. The VENT Spiritus 556i is the first consumer silencer from PTR to feature radial PIP venting. The use of PIP in silencer designs is adaptable; one particular benefit of its use is pressure bleed to atmosphere prior to final end-state orifice. PIP may be used to vent blast pressure prior to the end cap of the silencer. This allows intermediate pressure management throughout the internal flow; PIP porosity variation may be tuned for suppression through venting at different pressures. In various currently non-consumer VENT silencer systems for military applications (suppression of large caliber ammunition, multi-barrel electrically-operated gatling guns, or “miniguns,” etc) radial PIP venting is highly utilized. Early managed venting of blast pressure to atmosphere can pay significant performance dividends in such high pressure applications to the entire silencer system.
The VENT Spiritus 556i is shorter than the VENT 3, and thus benefits from radial venting in greater proportion. There is an important idiosyncrasy in radial venting of which the reader should be aware, as well as specific performance factors with regard to radial PIP venting. PEW Science laboratory testing in multiple 5.56x45mm combustion regimes has resulted in the determination of significant pressure sensitivity with regard to the resultant distal radial blast propagation for this particular design. At a critical pressure input, radial blast propagation becomes severe enough such that the external pressure field directly adjacent to the vent paths experiences meaningfully elevated amplitude. Below a critical pressure, the radial PIP vents function with a significant degree of wavelet dispersion and suppression efficiency increases dramatically. Muzzle suppression performance above and below this critical input pressure value can be examined directly in this report and the accompanying 14.5-in M4A1RIII evaluation of the PTR VENT Spiritus 556i (6.176). The 41% increase in barrel length from the MK18 to the M4A1 results in significant external pressure field changes with this silencer, directly adjacent to the muzzle.
PEW Science Research Note 2: It is extremely important to note that silencers possessing radial venting (whether that be direct-venting in legacy designs, toroidal or lengthened flow path venting in modern designs, or highly advanced staged PIP venting in the subject silencer) are at an inherent disadvantage in free field blast overpressure testing using MIL-STD 1474E pressure sensor locations. The PEW Science Silencer Sound Standard, which is an enhanced and strict interpretation of MIL-STD 1474E, utilizes a muzzle pressure sensor located 1.0 m left of the distal end of the silencer, 1.6 m above grade (silencer and sensor elevation). External pressure field shape from any suppressed small arm weapon system is a function of gas velocity, momentum profile, and multiple blast pressure origins, including the ejection port of semiautomatic systems. In the case of the PTR VENT Spiritus 556i, the twelve distal radial PIP vents add an additional blast propagation origin, directly in-line with the pressure sensor (a single point in the pressure field). Above the critical input pressure described in Research Note 1, their effects are directly measurable and displayed in test data. This phenomenon, along with other unique factors, characterize the Spiritus 556i performance:
The PTR VENT Spiritus 556i exhibits an unusually low free field blast pressure amplitude for its blowdown rate (Fig. 1a). Bolt carrier group return to battery is significantly delayed due to lower carrier velocity.
At high pressure input (e.g. 10.3-in MK18), muzzle flow precursors are well developed and relatively significant (Fig. 1b).
Typical exit event coupled jetting is present (Fig. 1b), followed by the aforementioned radial vent blast load coalescence (Fig. 1b, 29.8 ms). First-round-pop (FRP) propagation in the radial PIP exit events is well defined, and congruent with the expectation of flow origin within the silencer, in accordance with design reviews.
Free field blast pressure normalizes after the primary radial vent coalescence and significantly suppressed signature is maintained.
Again, it is extremely important to note that the radial blast venting load coalescence with the primary distal flow is exacerbated to due directionality; it is in-line with the pressure sensor. And, because of the nature of PIP venting and wavelets created from such flow gradients through the porosity, it is extremely likely that off axis propagation may differ in severity. This may result in a very localized zone of higher intensity. Therefore, the calculated muzzle Suppression Rating of 35.9 at the standard test location may trend higher (lower risk) immediately foreword or aft of the muzzle. Outside of the free field, this postulation is somewhat less relevant due to the complication of reflections. More laboratory testing is needed to fully quantify this system behavior. At the current time, extreme efficiency of the distal vents eliminating directionality concerns has been noted below critical input pressure (ref. 6.176). It is also important to view this phenomenon in context; the higher risk zone is still characterized by a 35.9 muzzle Suppression Rating, which is a relatively high level of protection on the MK18 weapon system.
PEW Science Research Note 3: High pressure input radial vent directionality phenomena notwithstanding, the PTR VENT Spiritus 556i is an extremely advanced 5.56x45mm rifle silencer. The holistic pressure field is significantly suppressed. The weapon operator is subjected to a shooter’s ear Suppression Rating of 31.0 on the standard untuned MK18 rifle, which is unprecedented for a system not utilizing HUXWRX Flow-Through technology. This is a significant technological performance achievement for several reasons:
The distal gas velocity from the PTR VENT silencers, and the Spiritus 556i, is significantly more controlled than that from a Flow-Through silencer. When fired outside of the free field, near reflecting surfaces, Flow-Through silencers may induce significant blast load reflections. The amplifying reflection factor, c_r, is directly proportional to both amplitude and angle of incidence; resultant reflected blast overpressures are often over twice as high as measured free field values. The wavelet distribution from PIP technology appears to provide superior reduction in reflection intensity when compared to overlapping toroidal lengthened-path Flow-Through technology. PEW Science postulates this performance differential will be apparent to users operating near berms, vehicles, awnings, structure walls, and other reflecting surfaces. Anecdotal user reports have indicated flat obstacles in the near field sized approximately 4-ft cubed (standard IBC chemical totes) present enough reflecting surface area for significantly noticeable signature severity increase with HUXWRX Flow-Through silencers. These reports are congruent with characterized blast propagation behavior in laboratory testing.
Possessing a low degree of blast load impulse accumulation near the muzzle orifice within the silencer is paramount to the efficacy of hybrid silencer design performance on semiautomatic weapons. The PTR VENT Spiritus 556i has extremely expedient early venting, allowing for blast load clearing off of the first reflector (blast baffle). Early and continuous venting, supplemented by the dynamically designed varying makeup of the PIP lattice regions, enables incredibly low ejection port blast amplification, even on an untuned host. Again, this is unprecedented for silencers other than Flow-Through models from HUXWRX, and certainly unprecedented for any silencers with a high degree of distal blast propagation momentum control, to this level. Even with the radial venting at the distal end of the VENT Spiritus 556i, the operator is subjected to less risk than many competing high performance models.
PEW Science Research Note 4: As with all PTR VENT silencers, in all tested combustion regimes, the VENT Spiritus 556i exhibits extremely minimal FRP. Complete masking of FRP from high fidelity instrumented PEW-SOFT test measurements is seldom possible. However, PEW Science engineering calculations indicate that the severity of the Spiritus 556i FRP on this weapon system is extremely similar to follow-up shots. Adverse FRP severity should not be a significant concern to operators or bystanders, in practicality, with this system.
PEW Science Research Note 5: With regard to relative performance factors, the muzzle Suppression Rating of the VENT Spiritus 556i is in the top 10 of the PEW Science laboratory MK18 Rankings, even with radial PIP venting. The shooter’s ear Suppression Rating, characterizing operator risk, is in the top 3 of the Rankings. The VENT Spiritus 556i is 6 inches long without a mount and is constructed entirely of Inconel. This is a significant development.
It is worth listing various other technologies in the hybrid design taxonomy. Differential flow rates in early and late-time are common characteristics of advanced hybrid designs in which elements of high flow rate designs are combined with more traditional geometries to throttle the rate of combustion gas propagation late enough in the time regime so weapon operation is influenced to a lower degree. Other examples of hybrid technologies and hybrid designs examined in the Standard research pedigree include (but are not limited to):
CGS Hyperion Technology - Hyperion (6.27), Hyperion K (6.28), Helios QD (6.13), SCI-SIX (6.101)
Surefire Total Signature Reduction - SOCOM556-RC2 (6.52), SOCOM762-RC2 (6.26), SOCOM556-RC3 (6.151), SOCOM-556-MINI2 (6.144)
CAT SURGE BYPASS - CAT ODB (6.120), CAT WB (6.129)
Liberty Precision Machine Tech - Torch (6.126)
SilencerCo LBP - Velos LBP (6.134)
PTR Purposely Induced Porosity (PIP) - VENT 3 (6.135)
KAC Pressure Reduction Technology (PRT) - KAC 556 QDC/CRS-PRT (6.156), KAC 556 QDC/MCQ-PRT (6.156)
FOR Systems Tech - Monarch 7.62 (6.155)
Sig Sauer Forward Flux - SLH300Ti (6.107)
Again, the above are classified as hybrid designs in the PEW Science research taxonomy. None of the above technologies or silencers are “Flow-Through” designs. That technology is only available from HUXWRX, and its principles of operation differ significantly from all of the above. Although some of the above silencers may be marketed as “Flow-Through” silencers by dealers and distributors that sell products, the physical mechanisms and performance differentials between all of the technologies are significant. The reader is highly encouraged to examine the in-depth laboratory testing and analysis of HUXWRX systems for a detailed description of pertinent behavioral factors. For example, when distal gas velocity increases significantly, as it does in a true Flow-Through design, there are consequences to the sound field that may induce unfavorable frequency components and reflection phenomena as discussed in Research Note 3. The Research Caution at the beginning of this FLOW 556 Ti test report elaborates on this phenomenon, with additional research references available.
PEW Science Research Note 6: It is likely that the durability of the PTR VENT Spiritus 556i is higher than many silencers on 5.56 NATO weapons. Due to its Inconel construction, the system is more resistant to particle erosion from high temperature and pressure jet impingement.
PEW Science Research Note 7: 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.
PEW Science Research Note 8: 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 95 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 9: 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 10: Note that the muzzle Suppression Rating of the PTR VENT Spiritus 556i is 35.9 and the at-ear Suppression Rating is 31.0; the same zone on the Suppression Rating Dose Chart. The lower back pressure of the VENT Spiritus 556i does contribute to a less severe ejection port blast signature, and the gas throttling technology in the silencer does slow blast propagation to reduce bystander hazard. The back pressure is low enough to reduce the ejection port blast loads to the shooter more significantly than with most other silencers on the standard MK18 weapon system. Weapon tuning may 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. Comparative analysis of holistic performance follows.
6.175.3 Suppression Rating Comparison (5.56x45mm from the MK18)
Figure 5 presents a comparison of the PEW Science Suppression Rating of the PTR VENT Spiritus 556i 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 5. Suppression Rating Comparisons of the PTR VENT Spiritus 556i and other rifle silencers, 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 variety of different silencers on the standard MK18 weapon system. The PTR VENT Spiritus 556i 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 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 PTR VENT Spiritus 556i produces free field bystander hazard reduction on par with that of several other hybrid designs such as the solid end cap Liberty Precision Machine Torch (6.126), Surefire SOCOM556-RC2 (6.52), the CAT ODB (6.120), and the long configuration of the PWS BDE 556 (6.123), with moderately higher performance than the CAT WB (6.129), HUXWRX FLOW 762 Ti (6.114), and Otter Creek Labs Polonium K (6.95). Note that off-axis performance of the VENT Spiritus 556i may be higher than its muzzle Suppression Rating reflects, due to the phenomena discussed in this report.
The free field operator (shooter) hazard reduction of the VENT Spiritus 556 with the standard untuned MK18 weapon system is elevated beyond most systems, including hybrid systems, such as the aforementioned vented Torch. The VENT Spiritus 556i outperforms most standard and conventional baffle system silencers in shooter hazard reduction, including the Otter Creek Labs Polonium (6.75), despite both silencers achieving relatively comparable free field bystander hazard reduction. All Polonium series silencers are outperformed by the VENT Spiritus 556 on the standard MK18 in operator hazard reduction due to their high backpressure. The higher early-time flow rate of the PTR system allows for significantly less ejection port blast propagation than most silencers on the standard untuned MK18.
Overall, in both bystander and operator protection, the silencer significantly outperforms legacy designs such as the Q Trash Panda (6.61). The designs of the two silencers represent completely different technological eras. Personnel risk reduction with the PTR system is of a different evolutionary step. Other primitive designs like the Energetic Armament ARX (6.82) and Rugged Razor 762 (6.58) produce a degree of personnel hazard that may be considered hazardous when compared to that of the VENT Spiritus 556i.
The muzzle Suppression Rating of the VENT Spiritus 556i is in the top 10 of the PEW Science laboratory MK18 Rankings, even with radial PIP venting. The shooter’s ear Suppression Rating, characterizing operator risk in the free field, is in the top 3 of the Rankings. The VENT Spiritus 556i is 6 inches long without a mount and is constructed entirely of Inconel. This is a significant development.
PEW Science Research Note 14: The PTR VENT Spiritus 556i represents a further evolutionary step in semiautomatic centerfire rifle suppression technology. Varying the configuration, location, and prevalence of PIP technology in the design is a powerful engineering tool. This type of parametric adaptation and flexibility appears to enable significant performance potentials. PEW Science postulates that further design advancement is not only possible, but likely. With length envelopes on the order of 6 inches; almost 2 inches shorter than previous VENT models, extremely competitive performance potentials may be demonstrated. PEW Science highly encourages the reader to examine the follow-on 14.5-in M4A1 test report with the VENT Spiritus 556i (6.176), in which the barrel length increase drops the pressure input below a critical threshold and significant muzzle suppression performance gains are noted, directly in-line with the pressure sensor.
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 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.
6.175.3 Review Summary: PTR VENT Spiritus 556i 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 PTR VENT Spiritus 556i with direct-thread mount achieved a composite Suppression Rating™ of 37.5 in PEW Science testing.
When paired with the 14.5-in barrel M4A1 and fired with Federal XM193, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 44.2 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 PTR VENT Spiritus 556i is a full size 5.56mm machine gun rated rifle silencer that exhibits highly advanced signature suppression performance and back pressure reduction. Constructed entirely of 3D-printed Inconel alloy, the HUB-mountable VENT Spiritus 556i also exhibits some of the most significant operator hazard reduction on the standard MK18 weapon system of any silencer evaluated by PEW Science to date. In combination with minimal FRP and strong distal blast momentum control, the Purposely Induced Porosity (PIP) technology in the silencer allows for high performance in a variety of environments with notable potential to continue to advance performance thresholds in the suppressed small arms state of practice.
The design of the VENT Spiritus 556i does share some similarities with that of the previously evaluated PTR VENT 3. However, notably, the VENT Spiritus 556i is almost 2 inches shorter than the VENT 3 and constructed of Inconel alloy instead of titanium alloy. Another significant difference between the two silencers is the radial venting present at the distal end of the Spiritus 556i. All PTR VENT silencers utilize Purposely Induced Porosity (PIP) technology both internally and at venting locations, including at the end caps. The Spiritus 556i includes twelve PIP vents around the outer circumference.
Multiple flow paths, including annular rerouting, are present in the VENT Spiritus 556i. As a staged design, the silencer does allow for high pressure blast load to propagate through multiple areas of the silencer simultaneously, and a significant flow path terminates at the distal radial PIP vents. PEW Science laboratory testing in multiple 5.56x45mm combustion regimes has resulted in the determination of significant pressure sensitivity with regard to the resultant distal radial blast propagation. At a critical pressure input, radial blast propagation becomes severe enough such that the external pressure field directly adjacent to the vent paths experiences meaningfully elevated amplitude. Below a critical pressure, the radial PIP vents function with a significant degree of wavelet dispersion and suppression efficiency increases dramatically. Muzzle suppression performance above and below this critical input pressure value can be examined directly in this report and the accompanying 14.5-in M4A1RIII evaluation of the PTR VENT Spiritus 556i. The 41% increase in barrel length from the MK18 to the M4A1 results in significant external pressure field changes with this silencer, directly adjacent to the muzzle.
Possessing a low degree of blast load impulse accumulation near the muzzle orifice within the silencer is paramount to the efficacy of hybrid silencer design performance on semiautomatic weapons. The PTR VENT Spiritus 556i has extremely expedient early venting, allowing for blast load clearing off of the first reflector (blast baffle). Early and continuous venting, supplemented by the dynamically designed varying makeup of the PIP lattice regions, enables incredibly low ejection port blast amplification, even on an untuned host. This is unprecedented for silencers other than Flow-Through models from HUXWRX, and certainly unprecedented for any silencers with a high degree of distal blast propagation momentum control, to this level. Even with the radial venting at the distal end of the VENT Spiritus 556i, the operator is subjected to less risk than many competing high performance models.
As with all PTR VENT silencers, in all tested combustion regimes, the VENT Spiritus 556i exhibits extremely minimal FRP. Complete masking of FRP from high fidelity instrumented PEW-SOFT test measurements is seldom possible. However, engineering calculations indicate that the severity of the Spiritus 556i FRP on this weapon system is extremely similar to follow-up shots. Adverse FRP severity should not be a significant concern to operators or bystanders, in practicality, with this system.
With regard to relative performance factors, the muzzle Suppression Rating of the VENT Spiritus 556i is in the top 10 of the PEW Science laboratory MK18 Rankings, even with radial PIP venting. The shooter’s ear Suppression Rating, characterizing operator risk, is in the top 3 of the Rankings. The VENT Spiritus 556i is 6 inches long without a mount and is constructed entirely of Inconel. This is a significant development.
It is likely that the durability of the PTR VENT Spiritus 556i is higher than many silencers on 5.56 NATO weapons. Due to its Inconel construction, the system is more resistant to particle erosion from high temperature and pressure jet impingement.
The PTR VENT Spiritus 556i is HUB mount capable, and includes a direct-thread mount. The user may adapt the silencer to a variety of mounting systems of their preference.
In this review, the PTR VENT Spiritus 556i 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.
