SSS.6.176 - PTR VENT Spiritus 556i and the M4A1 Mid-Gas 5.56x45mm 14.5-in Barrel Automatic AR15 Rifle (Free Version)
/PTR VENT Spiritus 556i on the M4A1 Mid-Gas 5.56x45mm AR15 with 14.5-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 PTR VENT Spiritus 556i 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.
PTR VENT Spiritus 556i testing and analysis on the standard 10.3-in barrel MK18 is documented here.
Section 6.176.1 contains VENT Spiritus 556i test results and analysis.
Section 6.176.2 contains overall gross Suppression Rating comparisons of the PTR VENT Spiritus 556i with other rifle silencers on the current market on the M4A1 Mid-Gas Rifle, including various configurations of the HUXWRX FLOW 556 Ti, Surefire SOCOM556-MINI2, KAC QDC/CRS-PRT, KAC QDC/MCQ-PRT, CAT/WB/A1, and Surefire SOCOM556-RC2.
Section 6.176.3 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, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 44.2 in PEW Science testing.
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 37.5 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
6.176.1 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
6.176.1.1 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 VENT Spiritus 556i are shown in Figure 1a. The sound signatures of Shot 1, Shot 2, and Shot 3 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. PTR VENT Spiritus 556i 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Pressure Signature
Fig 1b. PTR VENT Spiritus 556i 5.56x45mm NATO M4A1 Automatic Rifle Sound Pressure Signature
Figure 2a. PTR VENT Spiritus 556i 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
Figure 2b. PTR VENT Spiritus 556i 5.56x45mm NATO M4A1 Automatic Rifle Muzzle Sound Impulse Signature
An in-depth examination of the 5.56x45mm NATO suppression performance of the PTR VENT Spiritus 556i is published in report 6.175 in which it was tested on the PEW Science standard MK18 weapon system. Much of the same discussion, performance analysis, and gross behavior of the silencer outlined in that test report also apply to the tested case herein. In this report, the same silencer with the same muzzle device were tested on the PEW Science standard M4A1 weapon system. The differences between the two weapon systems are:
Barrel length (the MK18 possesses a 10.3-in barrel, whereas the M4A1RIII possesses a 14.5-in barrel).
Gas system length (the MK18 has a carbine-length gas port location, whereas the M4A1RIII has a mid-length gas port location).
Gas port orifice size (the MK18 has a 0.070” diameter gas port, whereas the M4A1RIII gas port has a 0.076” diameter).
All three of the above characteristics change the performance of the gross suppressed small arm weapon system, with any rifle silencer. Changes can be significant.
As discussed in the previous test report, 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 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.
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. As discussed in the previous MK18 test report, 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 environments 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 of 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. This was observed in MK18 testing with the 10.3 in barrel (ref. 6.175, Fig. 1b).
Below a critical pressure, the radial PIP vents function with a significant degree of wavelet dispersion and suppression efficiency increases dramatically. Muzzle suppression performance below this critical input pressure, on a 14.5-in barrel, can be examined directly in this report:
Note Figure 1b, above; at approximately 29.9 ms the blast load propagation exhibits significantly less additional jetting.
Furthermore, jetting normalizes earlier in time, when compared to the measured loads from the 10.3-in barrel. 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.
There is pronounced FRP throttle (~30.2 ms, Fig. 2b), as well as no post-FRP blast momentum accumulation rate change. Suppression efficiency is significant.
PEW Science Research Note 2: As previously discussed, silencers exhibiting radial distal 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 are not shown to adversely influence these direct in-line measurements on a 14.5-in barrel, when compared to on a 10.3-in barrel. This is a significant finding, because even with this radial distal venting, the PTR VENT Spiritus 556i achieves a muzzle Suppression Rating of 44.0 on the M4A1RIII host weapon system. This level of risk reduction, adjacent to the muzzle, is extremely high for the cartridge and system.
PEW Science Research Note 3: The muzzle suppression phenomenology highlighted in this study is even more significant when considering the level of early time flow rate through the VENT Spiritus 556i and its influence on operator risk. On the untuned M4A1RIII rifle, which possesses a 0.076-in diameter gas port at the mid-length position, the Spiritus 556i is still displaying signs of low back pressure behavior and ejection port blast reduction (ref. Fig. 4b, full report). While the silencer does not reach the level of operator risk reduction it does on the MK18, the two weapon systems are significantly different; the larger gas port and longer dwell time of the 14.5-in host results in an “over-gassed” system. Even with exceedingly high flow rates, achieving the same ejection port blast load reduction as possible on the MK18 is unlikely. This postulation is supported by analysis of the test results in this report, along with analysis of results from M4 testing of the HUXWRX FLOW 556 Ti (6.168) and CAT WB (6.130).
PEW Science Research Note 4: Many silencers possess “performance scaling” with varying input blast pressures. For example, it is likely that a conventionally designed simple cone-baffle rifle silencer will achieve a greater degree of pure muzzle signature suppression on a 14.5-in barrel 5.56x45mm AR15 weapon system than it would on a 10.3-in barrel system, all other things equal. However, as silencer designs become more complex, performance scales nonlinearly and sometimes may not scale until the barrel length delta becomes much larger. One common example of minimal performance increase with barrel length increase is the case of the Surefire SOCOM556-RC2 (6.128). For all intents and purposes, the muzzle signature from the Surefire silencer is relatively similar with both barrel lengths. It is postulated that high-pressure efficiency of the annular venting in the RC2 design is largely responsible for this behavior.
The PTR VENT Spiritus 556i is significantly complex, has multiple annular flow paths, and utilizes varying degrees of porosity in its PIP regions to achieve its performance goals. It is likely that such designs enjoy a suppression performance benefit with less severe input blast loads, but not a given. With the VENT Spiritus 556i, specifically, the distal radial vent porosity is a major factor. This factor, and the inherent critical pressure threshold that occurs somewhere between 10.3-in and 14.5-in barrel combustion input with this particular design, is responsible for the extreme muzzle Suppression Rating delta between the two tests. This is highly unusual and should not be extrapolated to other silencer designs. Reader caution is advised. The reader should not assume such performance deltas from 10.3-in MK18 to 14.5-in M4 are typical of all designs.
PEW Science Research Note 5: The first-round-pop (FRP) signature of the PTR VENT Spiritus 556i silencer on the 14.5-in barrel M4A1, to bystanders, relative to subsequent shots, is somewhat similar to that on the 10.3-in barrel MK18. This is a direct result of the use of the PIP technology. VENT silencers utilizing PIP exhibit extremely low relative FRP severity.
PEW Science Research Note 6: High flow rate silencer technologies can still not completely alleviate increased hazards on weapon systems in which the gas system delivers increased blast impulse in the unsuppressed state. The increased dwell time and gas port orifice size of the mid-length gas Daniel Defense 14.5-in barrel system create a more hazardous ejection port blast environment for the weapon operator. This is further discussed in the shooter’s ear data and analysis presentation in Section 6.176.1.2.
PEW Science Research Note 7: 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 90 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 8: 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 9: Note that the muzzle Suppression Rating of the PTR VENT Spiritus 556i is 44.0 and the at-ear Suppression Rating is 26.1; different zones on the Suppression Rating Dose Chart. The lower back pressure of the VENT Spiritus 556i contributes to a less severe ejection port blast signature. The back pressure is low enough to reduce the ejection port blast loads to the shooter more significantly than with many other silencers on the standard M4A1 weapon system. However, the native ejection port blast hazards from this weapon system are worthy of mention.
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, in which gross hazards and behaviors with the M4A1 weapon system are compared in the following section.
6.176.2 Suppression Rating Comparison (5.56x45mm from the M4A1)
Figure 5 presents a comparison of the PEW Science Suppression Ratings of the PTR VENT Spiritus 556i 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 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 PTR VENT Spiritus 556i on the M4A1 weapon system. Data is also presented for the fielding case of the 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 PTR VENT Spiritus 556i achieves significantly advanced 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 almost half a category higher than the nearest competitors which demonstrates extremely high performance. This occurs despite the somewhat lower performance of the VENT Spiritus 556i directly adjacent to the system muzzle on the short barrel MK18; this is due to the radial distal PIP venting of the silencer, its location directly in-line with the pressure sensor, and the critical pressure threshold discussed in Research Note 1 of this report and detailed in the previous MK18 test report (6.175).
The free field operator (shooter) hazard reduction with the PTR VENT Spiritus 556i on the standard untuned M4A1RIII weapon system is on par with that of the other high performers, despite being very high on the MK18. The M4A1RIII is an “over-gassed” rifle. Significant hazard reduction efficacy is extremely difficult to achieve without weapon modification. Nonetheless, it is important to note that the mechanisms by which the operator hazard reduction on the standard untuned M4A1RIII is achieved with the Flow-Through technology in the HUXWRX silencers, SURGE BYPASS hybrid technology in the CAT WB, and PIP in the VENT series are significantly different. The waveform parameters vary significantly as a result, and the Suppression Rating allows one to distill the overall severity into a single metric for free field hazard prediction. 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 exceptional muzzle Suppression Rating and distal blast momentum control of the VENT Spiritus 556i are likely to provide highly positive operator experience in a variety of environments. Any tuning of the M4 system for ejection port blast reduction will result in high levels of overall operator hazard reduction performance with this silencer.
The Surefire SOCOM556-RC2 with the 3-Prong flash hider provides 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 PTR VENT Spiritus 556i 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 reduction to both bystanders and the weapon operator.
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.
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.
6.176.3 Review Summary: PTR VENT Spiritus 556i 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, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 44.2 in PEW Science testing.
When paired with the 10.3-in barrel MK18 and fired with Federal XM193, the PTR VENT Spiritus 556i achieved a composite Suppression Rating™ of 37.5 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 short-barrel MK18 weapon system of any silencer evaluated by PEW Science to date. When used on the popular 14.5-in barrel M4A1RIII mid-gas rifle, its muzzle suppression performance is class-leading. 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 10.3-in MK18 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, and even with radial PIP venting, is at at the top of the M4A1 Rankings. The shooter’s ear Suppression Rating, characterizing operator risk, is in the top 3 of the MK18 Rankings and competes strongly with the highest performing silencers on the M4A1RIII. 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.
