Taming the bark of an Avenger

[Outer_Rondacker]

So anyone who has an avenger can see how a hollow chamber works to dampen the sound. Just take off the endcap and fire the rifle. You will quickly put it back on. Stock factor endcap. Even empty chambers work to some limits.

[TorqueMaster]

Bob,

The guys that are printing my designs asked me to reduce the volume of thread form, so that the threads don't have to be chased.  I prefer a full form that is chased, for strength.

Coextruding TPU to coat the inside of an LDC may have value.  Printing the whole LDC of TPU will have it droop into the projectile path.  Ditto for the whole structure ringing in such a vigorous manner that clipping is a risk.

Some of my designs included internal texturizing (images below) to see if these break up reflected sound.  While more experimentation should be encouraged, the measured reduction in peak sound was in the range of 2 dB.  In the noise, so to speak.   The downside was that the texture increased print time and file size.  This was for a Nova Liberty LDC very similar to the Avenger ones.  The printed texture of these LDCs already acts to reduce some sound reflection.  A softer printed texture added to a stiff structure might be just the ticket...

I have tested machined delrin toroidal spiral baffles in a 30 FPE .22, and they seem "twice as effective" as their expansion volume suggests.  So lets hope someone prints the larger version, above.  Perhaps I need to add dimples and a stem taper for a more appealing appearance...

I saw that bit about the threads -- it is unfortunate that FDM printing sometimes can't reproduce a model correctly, so the 3D model must be modified to correct for the printer's inadequacies.  For external threads, it's usually not too much of a problem.  Cura has a setting for how it slices parts at an angle -- "Slicing Tolerance."  "Middle" usually works ok but if threads are too wide they could try "exclusive" which reduces filament printed beyond the model boundaries.  INTERNAL threads are a pita...holes often get printed too small, and so do the internal threads.  There are workarounds in cura for that as well, but they may affect other model dimensions as well.

Interesting idea fusing TPU with PETG, using dual printheads.  Not impossible but have not heard of it being done.

How tight are your bores relative to the pellet diameter?  I don't visualize an all TPU LDC drooping very much.  Don't have the tools to simulate it, though.  EDIT-- it just occurred to me if such an LDC is contained completely or mostly within the shroud, there should be very little droop.  --END EDIT  Is ringing necessarily bad?  I assume that is expanding and contracting at some frequency?  Bad if it's a tin can, maybe not so bad it it's a rubber balloon?  It seems like one more way to temporarily store and release the energy...  I have to admit the physics and theories of these devices are like black magic to me -- difficult to visualize, let alone predict how/if they will work... 

Are your test designs for .22?  Are the testers using specific reg pressures and hammer spring settings and pellets for consistent comparisons?

[subscriber]

Bob,

I design for .22 because that is what interested parties are shooting.  I am using 7 mm bores inside the shroud and 7.5 mm at the far end of the 4" long external LDC - just to reduce the chance of clipping; as I don't know what the printed bore size actually measures.

The people testing usually declare reg pressure and velocity with a given pellet.  I am not going to insist that they use standards to please me.  As long as their set-up and test methods are stated.  I just have to interpret the data using fuzzy logic   . 

People make and test my designs without charging me.  I generate the designs as if I am being paid, but have not seen any cash yet.   What I get out of it is greater understanding.   That helps me with designs I do not share on open forum.     Even your latest post has suggested a way of making something that might be very useful, if it can be persuaded to work....

Using TPU for the sections inside the shroud should not present a problem, because the shroud becomes the load bearing part.

I don't mind adjusting thread models to what works.  Providing there is good feedback about where it falls short.  "Does not fit"  is a bit hard to diagnose...


Speaking of rubber LDCs ballooning, these videos may amuse you:

[subscriber]

I took my latest .22 Maxim LDC, refined it slightly.  Then increased the wall thickness of the forward section by 1 mm, in a dimpled pattern.  This is not a huge deal, but it might increase its unsupported stiffness, and general appeal.

I will pass on the STL to Chris, and anyone else that wants to print it.

[avator]

I'm amazed that this thread got this far....
I thought it was against forum rules to show how silencers were made.
I guess times, they are a changing.

[USAFANG6799]

I'm amazed that this thread got this far....
I thought it was against forum rules to show how silencers were made.
I guess times, they are a changing.

Is that because of "Under New Management"?
If so 'I LIKE'!

[TorqueMaster]

Bob,

I design for .22 because that is what interested parties are shooting.  I am using 7 mm bores inside the shroud and 7.5 mm at the far end of the 4" long external LDC - just to reduce the chance of clipping; as I don't know what the printed bore size actually measures.

The people testing usually declare reg pressure and velocity with a given pellet.  I am not going to insist that they use standards to please me.  As long as their set-up and test methods are stated.  I just have to interpret the data using fuzzy logic   . 

People make and test my designs without charging me.  I generate the designs as if I am being paid, but have not seen any cash yet.   What I get out of it is greater understanding.   That helps me with designs I do not share on open forum.     Even your latest post has suggested a way of making something that might be very useful, if it can be persuaded to work....

Using TPU for the sections inside the shroud should not present a problem, because the shroud becomes the load bearing part.

I don't mind adjusting thread models to what works.  Providing there is good feedback about where it falls short.  "Does not fit"  is a bit hard to diagnose...

Speaking of rubber LDCs ballooning, these videos may amuse you:
...

I have a .22 Avenger more or less idle right now (I'm concentrating on testing different hammer springs on the .177, as it seems to me to be wayyy oversprung for my purposes) so I should jump in on some of this .22 LDC testing too.  Weather will warm up soon and more time outside... I'll PM contact info for files.

Is there a preferred testing method.  I.e. away from buildings, sound meter X distance away from muzzle in Y direction?  Get readings with stock shroud and then LDC'd shroud for comparison?  And shoot at a quiet target so that readings are not tainted....am I missing anything?

So...yeah, holes printed on the XY plane (which is going to make the most sense for these) with FDM will print too small.  We usually expect the diameter to be 0.4 to 0.5mm too small -- your 7.0 is likely printing closer to 6.5.  (May be dependent on nozzle size, but most of us use 0.4mm.)  If nobody's clipping, great, but probably useful info if you want to future gnat's @ss it for air stripping...?

Sounds like a good way to collect data.  Hopefully with enough spitballing of ideas, something will stick.    For what it's worth, IMO models designed solely to test effectiveness do not need to be externally enhanced for visual appeal...just simple minimal OD cylinders are generally quicker to print and the material saving of dimples are probably pretty negligible... 

Interesting videos -- were they effective?  My ideal LDC would release the air with a slow hiss -- anyone remember Jonny Quest and Race Bannon's long range, nearly silent tranq rifle? Thhhhhhhhhh <slump>   Dangit I can't find a link to a video clip.

[subscriber]

Bob,

I like the test procedures already presented in this thread.   User Soupyyy has provided a lot of the data, so concentrate on his setup.  I am not insisting you duplicate it, but that you are aware that "trap sound being louder than muzzle blast" is not just wishful thinking; it actually happens with a good LDC. 

This thread includes how to ensure that you don't measure trap noise, and assume it is muzzle blast:  https://www.gatewaytoairguns.org/GTA/index.php?topic=197179.0

Rather than apply blanket policies for the accuracy of printed diameters, it is much better to print test pieces with representative diameters and measure them off your printer, with your set-up and material.   Adding 0.5 mm to an important ID should be done based in real info, not a guess.   That said, if prints are sloppy, I would rather the radial pellet to bore clearance be 1 mm, than 0.25 mm.

I agree that cosmetic dimples are a little silly for what is just a test piece.  The chief cost of such dimples is file size and print time.  I will PM you the download link to both the smooth cylinder and the dimpled version.

The bullfrog LDC videos belong to the GTA forum owner, Travis Whitney.   I have no idea if they were effective.  But, they are clearly "out of the box thinking".

You are closer to making you "hiss" idea work than you think.  It is close to a different tech I am working on in the background...

[WhatUPSbox?]

Cura has an option under Walls called hole horizontal expansion and you can give a positive or negative value. It applies it to all holes in each layer.

[WhatUPSbox?]

If you are going to do cosmetics, why do dimples when you can do DRAGONS!

[subscriber]

Nifty, Stan!

[stylnchris]

Still need to do some testing. 

[subscriber]

Looks good, Chris

[Outer_Rondacker]

Ok Peter, Well I picked up the corn cob as I am calling it from Chris this morning. First off was to do a sound test. Five shots with a full tank on the gun and same db device as before came in at 72. It does seam to make a whistle sound. Next was the on target test. Remember I am shooting the cheapest pellets known to dark side shooters. CPHP's. I picked a clean spot on my freshly painted steel plate and gave it a go from the rest. At 30 yards it piled up pellets in one spot. I dropped an entire mag with under a dime size result. I could not hang paper as its raining out. I am very certain its helping accuracy but and yes there is always a but. The moderator hits the fill port probe cover when screwed on all the way. Even with the cover off you can not fill the gun without removing the moderator. Honesty it has way to many threads to do so. It does seem to work just is not usable in its current design. Its to FAT and gets in the way of filling. So far the thingivers one is the smallest and at only one db different does not get in the way. I do not think the one from thingivers helps with accuracy much. I will say I had to look to see if the pellet had even left the barrel as it was drilling them in what would of been the same hole had I be using paper due to rain.
Hope this helps and thanks for all the hard work you put in. Outer

[subscriber]

Thanks Matt

Could you lay out an envelope shape that would not interfere with the fill process?

Are you suggesting that the threaded depth should be shorter?

Could you measure the Thingyverse device for length and OD; and shape that achieves desired clearance?

How does this latest design compare to the Thingyverse device when dry fired?  While this dryfire suggestion sounds like a silly question, are you certain that the trap noise is not being picked up over the muzzle?

How loud does it sound by ear, compared to other designs; assuming the trap is far enough to distinguish the sounds.  For loudness, tone and any other subjective measure important to you.

Thanks again

[Outer_Rondacker]

Yes Peter I can do all that for you but not sure if I will get to it tonight. Having dinner with the wife. As for trap noise I do not test sound while firing at a target. I put the shots down range with no target in a few hundred yards. Its all gun sound. To the ear it sounds like light. I am more impressed with the accuracy. Tomorrow I will try it again but I will be jacking the reg pressure up to 2400 psi and will push some 18.13 g pellets.

[subscriber]

Thanks Matt

Your sound testing is ideal for eliminating trap-slap.

I am working on a different design, so no hurry with the measurements - although they may also be pertinent.

[TorqueMaster]

Bob,

I like the test procedures already presented in this thread.   User Soupyyy has provided a lot of the data, so concentrate on his setup.  I am not insisting you duplicate it, but that you are aware that "trap sound being louder than muzzle blast" is not just wishful thinking; it actually happens with a good LDC. 

This thread includes how to ensure that you don't measure trap noise, and assume it is muzzle blast:  https://www.gatewaytoairguns.org/GTA/index.php?topic=197179.0

Rather than apply blanket policies for the accuracy of printed diameters, it is much better to print test pieces with representative diameters and measure them off your printer, with your set-up and material.   Adding 0.5 mm to an important ID should be done based in real info, not a guess.   That said, if prints are sloppy, I would rather the radial pellet to bore clearance be 1 mm, than 0.25 mm.

I agree that cosmetic dimples are a little silly for what is just a test piece.  The chief cost of such dimples is file size and print time.  I will PM you the download link to both the smooth cylinder and the dimpled version.

The bullfrog LDC videos belong to the GTA forum owner, Travis Whitney.   I have no idea if they were effective.  But, they are clearly "out of the box thinking".

You are closer to making you "hiss" idea work than you think.  It is close to a different tech I am working on in the background...

I'll go back and re-read on "best testing procedures."  I probably read those before I had an Avenger and haven't revisited them recently.

Agreed, you shouldn't change dimensions blindly, but I still suspect the prints being tested may be tighter than you think.  Difficult to measure.  One could do a partial print to measure the tighter diameter.  I also thought using drill bits as "go/nogo" gages might be "adequate."  I have a relatively cheap set from harbor freight that goes every 1/64th inch -- that's about 0.40mm...  a 7.0 mm hole should pass a 17/64" (6.75mm.) If it doesn't pass, you know there's at least 0.25mm less diameter than you expect...   The 7.0mm hole should have .75mm clearance around a 5.5mm pellet...I expect they could be printing closer to 6.5mm resulting in a 0.50mm clearance.  This is all moot if they are using "hole horizontal expansion" and it is working correctly...  Further, if there's no clipping, I guess no harm no foul.

Cura has an option under Walls called hole horizontal expansion and you can give a positive or negative value. It applies it to all holes in each layer.

I have read that that feature is hit or miss on what it identifies as a "hole" but yes, it may solve any issues here.  Have you used it, does it work ok?    I'm still using an older version without this feature.

[jaraxle1zx]

Helped my friend pick out a bull pup avenger 22 cal for his 1st airgun.
When I bought my M3 impact I also got the Donny FL add on for cheap.
I just ordered a fat boy for the impact so I’ve got an extra moderator for the avenger.
Ordered the Donny Fl avenger moderator adapter so I’m hoping I’ve got the bark calmed down on the avenger from day one when it gets delivered next week

[WhatUPSbox?]

I have used the hole horizontal expansion feature, typically with partial/section test prints to get a snug fit.