Taming the bark of an Avenger

[stylnchris]

[subscriber]

Thanks Chris,

There is something weirdly satisfying about seeing one's idea come to life.  At first, familiar, then the realization that it is denser than just vaporware.

I may be biased, but that looks pretty good.  Of course, the printer and operator have a lot to do with that.  Now, to see if it has functional value on an Avenger...

I notice one little strand across the center of the bore on the rear view .  Something that can't have much effect.

[avator]

It's threads like this that position me at the rim of yet another rabbit hole..... 

[stylnchris]

Peter,

I have tested the v4 (front) and the one with the vents on the side with a sound db meter app on the iPhone and both of them with the holes are coming out at 85 db.  I took a hot melt glue gun and blocked the holes on the v4 ldc with forward facing holes and that bring the db's down to 75db. 

The original stock is 84 db.   

I think you need to go back to blocking the holes as they are not needed. 

The thingiverse LDC was 73db  (for the record).

I would like to print the v4 again with blocked holes from the print (rather then putting hot melt glue in it).   

Just trying to "dial it in for you"

Sorry & Thanks,

Chris & Outer_rondacker.

[WhatUPSbox?]

Did the forward vented version sound different (not as sharp)?

[stylnchris]

I've blocked the holes on the forward version with hot melt glue.  Once I did that it wasn't sharp at all.   Before I think it was still sharp.    Outer_Rondacker has the 2nd one I printed with the holes not blocked by hot melt glue so he could probably do an "instant replay" and give a more percise answer.  maybe there is a way that we could record it with the iPhones sound recorder and post the wav files?   Then you could attempt to hear for yourself.

WhatUPSbox did you print one?

[WhatUPSbox?]

Unfortunately sound files aren't one of the allowed file types  (though there is an mpg option).

I don't have an Avenger but have printed shroud interiors for another gun. There has been a discussion on whether disguising the sound is effective in making an airgun backyard friendly or if Db reduction is all there is to it.

[Outer_Rondacker]

I have just returned from stylnchris house. Long day testing Peters designs. To much pumping by hand.

Lets see, First off let me start by thanking Peter for all his hard work and others who have contributed to the designs. Like Chris has said the moderator with the holes on the sides and on the front was considerable louder to the ears and the neighbors dog. With that said we plugged the wholes on the one and gave it a go. It was a lot better. I then downloaded a db APP on my phone and we did more tests. The strange part is Peters earlier designs tended to work better without the wholes. The stock design was lower on the db meter app than the design with the holes. So buddy it was as great idea but turns out it made the bark worse. Hey you never are going to know until you try. So we did.  We are printing a design with 1/2 x 20 threads on the end so an external ldc can also be added. This is just for testing fun and to see just how low it can go.

More info I should add fast. We ran the Avenger at 1750-1800 psi on the reg with 1.5 turns of hammer spring. Shooting CPHP's 14.3 Our avengers are Eco tuned for lighter pellets. It is funny you can hear the pellet whistling in the air.

I am really enjoying this and hope to keep testing. (if Chris doesnt run out of filament to soon). Once the weather breaks and the compressor shows up I think we will be able to put more time into this. For now its going to be slow.

[swoab47]

I have just returned from stylnchris house. Long day testing Peters designs. To much pumping by hand.

Lets see, First off let me start by thanking Peter for all his hard work and others who have contributed to the designs. Like Chris has said the moderator with the holes on the sides and on the front was considerable louder to the ears and the neighbors dog. With that said we plugged the wholes on the one and gave it a go. It was a lot better. I then downloaded a db APP on my phone and we did more tests. The strange part is Peters earlier designs tended to work better without the wholes. The stock design was lower on the db meter app than the design with the holes. So buddy it was as great idea but turns out it made the bark worse. Hey you never are going to know until you try. So we did.  We are printing a design with 1/2 x 20 threads on the end so an external ldc can also be added. This is just for testing fun and to see just how low it can go.

More info I should add fast. We ran the Avenger at 1750-1800 psi on the reg with 1.5 turns of hammer spring. Shooting CPHP's 14.3 Our avengers are Eco tuned for lighter pellets. It is funny you can hear the pellet whistling in the air.

I am really enjoying this and hope to keep testing. (if Chris doesnt run out of filament to soon). Once the weather breaks and the compressor shows up I think we will be able to put more time into this. For now its going to be slow.

Thanks for the description of what these are doing.

I do think that the two latest designs are aimed more towards maximum air stripping and not sound moderation, so they might do exactly what Peter was hoping for . (I could be wrong)
Did you guys shoot groups as well as test the DB levels?
I'd like to see if there is a noticeable difference in accuracy between the different mods.

I have a friend that is going to print some of these out for me, I can't wait to try them out.

Happy Shooting!

[Outer_Rondacker]

Today was sound only no groups. Once the weather gets a bit nicer we will be testing groups as well. Today it was flurrying and blowing. Its just to cold to.

You could be correct as I am looking to tame the bark. I just giving feedback as I have it. There will be more testing.

We just got done printing one from the thingiverse (not peters) that had external threads and the cap that printed with it does not even come close to fitting. So one never knows what going to happen when printing something.

[subscriber]

I do think that the two latest designs are aimed more towards maximum air stripping and not sound moderation, so they might do exactly what Peter was hoping for .

Chris and Matt,  Thanks for the feedback.  And the effort.

Andrew is exactly correct that the frontal holes were to direct air out away from the projectile path, NOT for sound reduction.  I can find my statements to this effect higher up in this thread, and in emails exchanged with your guys, but this is not a legal intervention

I am guessing that the notion that the latest design must be the best one is what motivated you to lead with the four stage air stripper, rather than the Shorty LDC.  As long as the Shorty LDC yielded at least a 10 dB sound reduction, then it did exactly what I predicted: to halve the apparent sound level.

If Chris is willing to print other versions, and there is a market for shroud extensions, then I am willing to create the files for such.  Just specify the maximum length ahead of the shroud and the max OD.

My suggestion is for a 2" extension at shroud OD.  What is the exact shroud OD?  26 mm?

[subscriber]

You guys may have vindicated a statement I made about the tiny holes that are so popular in the sides and rear of commercial LDCs and shrouds:  I said that holes large enough to actually flow air would be louder in the direction of the holes (so possibly quieter towards the front, but louder to the side). 

I also stated that small vent holes would make no difference whatsoever.    Seriously, the small holes are for visual appeal.  Because name brands have them, other brands are expected to have them.  These small holes are nothing but "racing stripes"...

So, you have confirmed what any person with a muzzle brake on centerfire rifle already knew:  That venting high pressure gasses sideways is louder than a conventional muzzle.  You should think of my four stage air stripper as a muzzle brake, rather than LDC. 

I presume you have seen my full length version of the Avenger/Liberty LDC with the dimples?  It is 104 mm longer than the shroud, and has a 30 mm OD.  It is twice as effective as the Shorty LDC:

[x3baddad]

that looks awesome, I want one on my Avenger

[subscriber]

So, I went ahead and conjured a Plus 2" Avenger LDC.  The forward two inches are 26 mm in diameter, with the inside the same as the in-shroud chambers.  This increases the wall thickness of the forward section to make it more robust.

I predict a 6 dB sound reduction over the Shorty LDC (not the devices with forward vents).

Images attached.

I will email the STL to Chris (and anyone else who asks for it, with their email via PM).

[avator]

Not for nothing guys but, the last time I heard a pellet whistling was due to it clipping the muzzle break on the way out. This was on my Air Speed before I got it sorted out. You may want to check for signs of clipping.

[Outer_Rondacker]

Peter looks great. Like I said we were only testing for sound today. To cold to punch paper.

Avator, I just put my bore scope up to the parts tested and I do not see any signs of clipping. I will keep an eye out for it. Hopefully next week I can get some testing on paper once the snow stops.  If I have clipping I think the paper will tell the story. I hope anyway. I just want it to be above freezing out.

So since I am new to anything other than my 16+ year old disco with Mikes TKO brake on it. I take it air stripping helps improve accuracy?

Guys I just happen to have a friend with a printer sitting on his desk collecting dust and recently talked him into buying his first air gun. No one was criticizing anything just reporting back what we have so far. Tip of the iceberg to say.

[subscriber]

I take it air stripping helps improve accuracy?

No one was criticizing anything just reporting back what we have so far. Tip of the iceberg to say.

Generally, the more potent the airgun the greater the muzzle blast (certainly true with PCPs and pumpers).  The blast that occurs as soon as the pellet is clear of the muzzle actually tries to flip it over because that air is moving faster from the rear (pellets are designed to have air flow front to rear keep them pointing forwards).   Therefore diverting PCP muzzle blast away from the projectile path tends to reduce group size.

Most shrouded PCPs have an air stripper that diverts air towards the rear of the shroud.  Any additional baffles scrape off some more air from the path of the pellet.   

The spacing from the barrel muzzle of the primary air stripper is a compromise.  My two stage air stripper is intended to reduce that compromise, between retaining maximum pellet stability, and maximum sound reduction via diverting air into the rear of the shroud.

Many low power target PCPs have air strippers that just vent off to the side.  Their goal is to help reduce group size.  There is so little blast on 10 meter target PCPs that one might question how much they help with group size.  Certainly, sound is not a problem on 5 FPE airguns.

I appreciate the effort you guys put in to make and test my designs.  I appreciate hard data, and honest feedback.  My comments were intended as an light-heated poke, because apparently you had not read the notes I posted describing the purpose of each design.  I attribute that to your enthusiasm to get cracking with making and testing.  Can't fault you for that. 

I hope you are eager to try the LDC version that is 2" longer than the shroud...

[Outer_Rondacker]

Guilty Peter, I quickly scanned the many emails you sent me before forwarding to Chris to print. I did miss the part about not being for sound moderation. I just kinda figured since this thread was about Taming the bark of the  Avenger that it was for just that. Chris and I both have very limited time now and days and honestly I will say I missed that part. I do believe Chris has every intention of printing the new design this morning. Keep up the good work. I wish I had the software to attempt to do what you are doing. It would most likely not turn out well and cost Chris a small fortune in filament printing my screwups.

[WhatUPSbox?]

Just as an aside, I ran across this video that explains some of the tolerancing options in CURA. May explain some of the thread fit results. I have not tried this yet.

[WhatUPSbox?]

In thinking about the airstripper and sound moderation functions, I went back to this video (best played at .25 speed).
I don't know what gun that is and what caliber (though I guessed .177)
I then took a few screen shots and overlayed a scale with pellet diameters (estimated) as the units. If it is .177, then 6 units is a little over an inch.
To me it looks like the air behind the pellet has structure for maybe the first 10 or 12 units and suggests that if you have baffle openings at the 1 and 2 inch points, then perhaps after that you just want volume until you get to the exit.
Unfortunately, highspeed cameras are hard ($$$) to come by, so getting videos for an Avenger for example is not likely.