Taming the bark of an Avenger

[subscriber]

Bob,

The exact distance for the mic is not cast in concrete (as long as it is repeatable once accepted as standard).  Far enough not to clip. 

Off to the side at 50 yards may be too quiet, unless you fix the gain at a higher level.  If that does not work, then closer, but without risk of clipping.

Just thought that it would be interesting to compare downrange at non sound level clipping distance, with same distance off to the side (and same gain).  Because that tells us how directional the sound is, and if the delta or ranking between LDCs is the same for both positions.   We assume the ranking would be the same, but if the LDC body acts as a speaker in one instance, the sound reading may be higher than its muzzle facing ranking suggests.

[WhatUPSbox?]

You may be able to reduce the response of the mic in the downrange test by changing the orientation with respect to the muzzle. Audacity has a slider for adjusting the mic input but this does not address the ADC on the android side or even if you are recording with Audacity on a laptop, I'm not sure it addresses the soundcard process.

I'm not sure you need a separate reference sound generator. If you have a configuration that's easy to re-establish (maybe the printed cap but no LDC) then just doing repeatability shots periodically in your test sequence should let you know if the instrumentation scheme is stable on a particular day. For convenience, I just use a separate gun (P17) for the repeatability checks.

It was interesting in your file, in the louder shots (like the first one), Playing the second 150 ms of the shot still produced a reasonably audible shot sound even though the db's were significantly reduced. Your metal target shots illustrated why target distance can matter.

[subscriber]

The target "ding" acts as a useful reference sound.    The flight time lag from "pop" to "ding" also acts as confirmation that muzzle velocity is the same between shots.  At least, not different enough to raise questions about the reason for differences in muzzle blast; other than different LDC states.

[ER00z]

All of the work going into this is simply amazing and has been a good read so far.

I don't have an Avenger, but an Origin which I believe has the same (or very similar?) barrel & shroud assembly. I went with a third party setup (Donnyfl) to center the barrel and keep the db's down (very effective), but have found all this very interesting.

As an outsider looking in, It would be interesting to see two final variations come from all of these trials, one that extends from the shroud 4"-5" for maximum db reduction and one that is just extends past the shroud enough to tighten (an internal design). Design both to center the barrel, as I believe its a nessesity as my particular example was way off and others may encounter similar.

P.S., if you 3D printer guys need a guinea pig for barrel band designs, send me a PM, Lol. I'd like to buy a thin/plain wide band (3"to 8", no rails/etc.) but I don't do PayPal/eBay/etc., and I'm sure others might be in similar situations...

[subscriber]

The target "ding" acts as a useful reference sound.   

That said, the last recording seems to have the muzzle report about as loud as the target ding.  Any LDC quieter than that will have the target noise keep the peak measured level at the target's peak level.  So, another form of measurement clipping - that needs to be avoided by meter placement, and or a quiet trap. 

At least with the full sound recording, one can separate the report from the target noise, due to the flight time delay to 50 yards.

[subscriber]

Zack,

Which DFL LDC did you go with?   Could you please post pictures showing it installed, and removed from your air rifle; including the internal adaptor?  Do you have to remove the LDC to air fill?  If so, does that affect you desire for LDC diameter?  To avoid removal for air filling, 26 mm seems to be the max OD; or it needs to have a bottle neck shape in front of the shroud.

My latest designs with a coarse thread for rapid removal have grown to 38 mm, or 1.5" in OD.  If a given design seems "good", I plan to do an integral design with the internal shroud airstripper bits.  That would be more tedious to remove and replace for air filling; unless the two piece design is favored by Avenger owners.

[ER00z]

The Umarex Origin, to my understanding uses the same shroud and possibly barrel as the Avenger. It does not fill in the front of the cylinder, but instead  closer to the trigger guard via fill probe (no hindrance from any sized moderator).

The moderator is a Tanto, combined with the newer adapter design. I believe the moderator O.D. is 30mm (1.22 inch listed). The adapter extends some, possibly to make filling the Avenger easier with either a Tanto (5" length) Or Koi (7"length) moderator (both 30mm O.D.).

Anyways, here's some photos

[subscriber]

Thank you, Zack

How does this setup group, compared to stock?

[ER00z]

Groups are fantastic with this setup, except they shift around with shroud movement. These guns (Avenger/Origin) are capable of sub1.5" at 100 yards on a calm day, or at least my example is. In stock form this particular gun had a "droopy barrel" within the shroud. There was possible pellet clipping on the OEM muzzle cap, but just barely if any. It seemed to group ok out of the box.

[WhatUPSbox?]

There are a couple of barrel band designs on Thingiverse
https://www.thingiverse.com/search?q=avenger+barrel+band&page=1&type=things&sort=relevant

[TorqueMaster]

As an outsider looking in, It would be interesting to see two final variations come from all of these trials, one that extends from the shroud 4"-5" for maximum db reduction and one that is just extends past the shroud enough to tighten (an internal design). Design both to center the barrel, as I believe its a nessesity as my particular example was way off and others may encounter similar.

P.S., if you 3D printer guys need a guinea pig for barrel band designs, send me a PM, Lol. I'd like to buy a thin/plain wide band (3"to 8", no rails/etc.) but I don't do PayPal/eBay/etc., and I'm sure others might be in similar situations...

Ultimately that may be what I am after as well.  If an all internal is "quiet enough" I'd prefer not to have extra length hanging out there -- I'm definitely getting VERY spoiled by the longer ones though.

I'm also looking at buying/designing/printing another barrel band for my Avengers.  I have shimmed the original with electrical tape, and that has cured 90% of my poi changes, but there is still a lack of rigidity at the muzzle, the barrel/shroud can still "rotate" (the motion feels more an arc than linear) around the air tube.  A second band will help, and if neither the shroud nor air tube can rotate inside the band, even better.  It'd be trivial to draw up and print, but I haven't taken time to come up with a design I'd like visually.  It will NOT use the (imo) near-worthless grub screw concept on the original band.  Before it's over I may replace it too.

On the Avenger the shroud and air tube ... I'm going from memory.. are 25.0 and 25.1mm OD respectively, with a 1mm (give or take) gap between them.  Is the Origin essentially identical there?

[ER00z]

Those dementions seem correct, by the best I can measure (no calipers available).

Funny you mentioned Electrical Tape, I came up with this last night...
Electric tape, two dead AAA batteries and a 25mm x 2.4mm o-ring
(Untested as of yet)

[JimD]

Zack,

I mentioned a couple printed moderators I got from another member on page three of this thread, I think it was reply 57.  Both were quieter than my Tanto with the one that is all inside the shroud the quietest.  It is what I am using.  I know nothing about the design except they work. 

Jim

[TorqueMaster]

Groups are fantastic with this setup, except they shift around with shroud movement. These guns (Avenger/Origin) are capable of sub1.5" at 100 yards on a calm day, or at least my example is. In stock form this particular gun had a "droopy barrel" within the shroud. There was possible pellet clipping on the OEM muzzle cap, but just barely if any. It seemed to group ok out of the box.

Today I scouted my property for a good place for 100 yards -- and was able to create one with minimal...landscaping.  Starts on a solid concrete pad, too so I'll be less likely to get ate up by bugs.  With my .22 Avenger, I'm nowhere near 1.5" groups, as I'm handicapping myself with CPHPs, which seem to have at least one crazy flier every magazine, but the majority are hitting about a 4" circle.  NUAH should be mine soon.  Sooner if I switch pellets.  For fun, I set a 45 yard Ram silhouette out at 100.  Figured I should be able to get it with a full magazine.  First shot.....tink!  Pure luck but dam I love this gun.

I did one brief recording, just to see if a) the pellet hitting the paper/cardboard target face would be audible at 100 yards away (it is), and b) if there would be any noticeable echo from the house directly behind me (not that I can tell.)   Vinyl ("polymer") siding.  Had the plume 2-piece installed, and the phone right next to the gun.  I think all you mostly hear is the hammer hitting the valve.  I should try recording dry "firing" with no air sometime for comparison.

The timing from the recording seems spot on.  Estimated 900ish fps .22 CPHP.  Online calculator says should hit the target in 0.44 seconds.  Audio shot peak to hit peak is about .705 seconds.  Figure speed of sound for pellet hit audio coming back 100 yards... 300ft/1125ft/s... is 0.267 seconds.  Added to 0.44 is 0.707 seconds.  Woot!

[subscriber]

Zack,

I mentioned a couple printed moderators I got from another member on page three of this thread, I think it was reply 57.  Both were quieter than my Tanto with the one that is all inside the shroud the quietest.  It is what I am using.  I know nothing about the design except they work. 

Jim

Jim,

Your post you referred to is here:  https://www.gatewaytoairguns.org/GTA/index.php?topic=196584.msg156305238#msg156305238

It would be great if your results are repeatable.  It would be even better if John (runner57us) would participate here.  Now, he may have found the holy grail, and not want to share his magic.  That is OK.  Else, we could learn a lot from how he seems to get away with, what seems like breaking the laws of physics.

Other than highly effective sound mitigation with John's device, how well does it shoot?

[subscriber]

Bob,

Having a 100 yard range in your backyard must be fun.  I can only dream about that.

[subscriber]

So,  I chased down all leads from Jim, to John to Benelliboym1.  John posted to this thread about the Binelliboym1 Avenger LDC, and user Soupyyy had some designs based on it.

My position is that I can't argue with results; even if "it can't work"; or "will provoke some unacceptable side effect".  I dismissed the Binelliboym1 design because "it is too leaky", with air from the shroud space getting ahead of the pellet via the slits along the sides - image below.

Such leakage seems anathema to air stripping, so, from my perspective potentially blowing groups; or not helping them.  Yet, such bypass air may very well be the secret to the Binelliboym1 working better than its small volume suggests possible.   How might this work? 

I know there is a "user concussion reducing" patent for a field cannon that has a deliberate flow path at the throat, with channels that allow more high pressure gas to pass ahead of the loaded projectile on firing than is usual.  On the face of it, this is wasteful and would drive more throat erosion.  Yet what is claimed is that by leaking more gas at a higher pressure ahead of the projectile, results in the air at the muzzle being more gently pushed aside, by what amount to a more gradual pressure ramp, than being slammed abruptly by the high pressure gas uncorking from behind the projectile. 

The slam that normally occurs, still occurs, but that gas encounters a mix of air and gas that is already at a pressure substantially higher than one atmosphere, so the pressure drop is smaller than would otherwise be the case.  Hence, more of a triangle wave than a square wave; and less concussion to the crew firing the gun as a result.

Now, just because something is patented does not mean it works, but let us assume it works as explained.  If so, the Benelliboym1 LDCs may work by turning the report into more of a rushing sound, than a popping sound.   The traditional way of achieving this is to stretch the period of air release, after the pellet has gone; rather than stretch the time by starting air release early.    Now, if these LDCs group well enough, then it may be that I am chasing improvements that are superfluous to requirements. 

Then again, Bob has not tested one of these Benelliboym1 LDCs yet .  If they are better than the much larger and more expensive DonnyFL products, that is indeed significant.  And worth celebrating.


Here is an ebay listing with images of the Avenger LDCs of this Benelliboym1 design:
https://www.ebay.com/itm/Price-Drop-Air-Venturi-Avenger-177-22-and-25-Cal-Barrel-Stabilizing-Moderato/124666298353




Similar design for Flashpup, with tighter than usual bore diameter measurement:
https://www.ebay.com/itm/END-OF-YEAR-SALE-Monocore-Baffle-System-for-AT44-QE-Flash-QE-Flashpup-QE/125053960010

[subscriber]

Found it:  Muzzle blast reduction, by means of increasing gas leakage ahead of projectile: 

https://techlinkcenter.org/technologies/weapon-blast-attenuation/a2cef892-1ab8-45d2-80c8-c29857621326

A method to attenuate the blast wave/blast overpressure from a weapon discharge by leaking an effective quantity of propellant gas from behind the projectile, into the precursor gas flow in front of the projectile, while the projectile is still in the weapon barrel—whereby the exit pressure ratio of the projectile from the weapon is surprisingly reduced by about 95%—resulting in a reduction of from about 51.6 to about 58.2% in the peak pressure level/sound wave which impacts the user or crew of the weapon.

I was contacted in 2019 with an offer to license DOD tech in a medical device field.  In researching the info offered on TechLink, I found the artillery IP referenced above:

[JimD]

My groups are, if anything, a little tighter with the in-the-shroud moderator than with a DonnyFL.  But that is probably random variation of the shooter.  I think both are neutral on my accuracy - no positive or negative effect.  The only moderator I noticed an apparent accuracy benefit for is the Buck Rail on my Prod.  I wonder what it's design is like.

Another factor that may or may not be significant is the back of my shroud has small holes.  I added them when I was messing with my own modifications in the shroud since my P35 has holes and works well.  I have not had my hand up around the holes when shooting with the Avenger but I've noticed a puff of air coming out of the P35 shroud.  Could the holes help offset the small volume?

I've also been shooting mostly and possibly totally at 25 yards since installing this moderator.  I can try it at 33 yards easily but that is as far as I can go in my yard. 

Jim

[Mr.P]

This sounds like a Tesla diode in some ways. I’ve been printing baffles for a while that split air to two streams one peripheral and one central.  The walls are contoured to direct the air smoothly. This is what I use in my home made airforce shrouds and they work well enough that I stopped making further designs for those guns after that point. 

I’ve included a picture of one of them - there are two parts on the left, the parts combined in the middle and then a cut away view on the right.  The one pictured is for a relatively tight space for 357 airgun.  This is a prototype of something i was trying a while back, not a finished design.