LDCs that screw directly into the Airacuda Standard shroud

[subscriber]

Considering Jack's request for more generous internal corner radii, I have created such a version of the LDC that has the wrap around blast chamber, and larger front expansion chamber.   The point of the large radii is to create a smooth reverse airflow, driving some Tesla Valve effect.

See image of cross-section below.

STL attached.  This has an M22 x 1 mm thread.

[subscriber]

OK; so M23 x 1 is not a standard size.  Apparently none of my threads are a standard size 

[jackssmirkingrevenge]

Biggest issue may be getting a good sealing surface with a 3D printerd part.

I don't think that would be a problem, in fact it could be an advantage - a slightly leaky seal would provide sufficient obturation to reduce the sound while also allowing the excess pressure to leak out slowly once the projectile is clear.

This is how I picture an idea setup, with barrel being ported to ensure gas can fill that first chamber before it has a chance to escape to the atmosphere:



By the way apologies to subscriber for having derailed this thread with a discussion of this principle, perhaps a new one ought to be started.

Considering Jack's request for more generous internal corner radii, I have created such a version of the LDC that has the wrap around blast chamber, and larger front expansion chamber

That looks really good and personally I think this philosophy is optimal in theory; the first chamber accessible by the gas is of maximum volume, while all the subsequent chambers are small and serve only as "plugs" to ensure that the bulk of the gas has time to expand and lose pressure in that first chamber before it can exit.

[oldpro]

 My apologies there's NOTHING wrong with the threading. I tried some new filament and it has major shrinking. Back to my old Overture PETG.

[avator]

Travis.. would you kindly post a picture of the LDC on the gun for a visual reference?
Thanks.

[subscriber]

Thank you, Travis

[subscriber]

Jack,

I appreciate that you are a clever ideas guy that has made a bunch of working models.  That said, there may be two aspects getting in the way of your ball valve in the barrel concept as shown above:

1. Air flowing over a ball from a conical or spherical seat, is notorious for drawing the ball back onto the seat, rather than pushing the ball out of the way, due to the Bernoulli Principle:



2. Making ports in the barrel is not going to be popular, as removing burrs on the inside would be difficult; and the reduction in bend strength undesirable.   I would set a goal that no stock parts be modified for any new invention, unless you manufacture the whole system.

If I could make burr-less holes in a barrel (via EDM perhaps) I would populate the last 6" of a PCP barrel with 2 mm diameter holes at a 6 mm center to center spacing.  Then enclose that area in a casing with walls partitioning off the discrete air volumes, perhaps 1.5" long.  This way, you have a place for the air to get out of the barrel and expand more gently and progressively, than the simple uncorking of the pellet from the muzzle.  Notice that there is no mention of valves or balls, because they would add very little functional value. 

So, an integral muffler that is perfectly aligned with the barrel bore, and adds no forward length.  But it will steal some velocity from the pellet, so start with a barrel that is long enough for purpose.  Dandy, but expensive.

For the hobbyist lacking access to an EDM machine, filling that section of the barrel with chamber casting Bismuth alloy, then drilling the holes with a new short 2 mm diameter endmill in a milling machine should minimize burring by supporting the steel as the cutter breaks through into the bore.  Then afterwards simply melting the Bismuth alloy out as these melt at very low temperature.

Ultimately, simple is best.  But, there is no penalty for considering new ideas, and then analyzing them later for viability. 

Below is an airgun muffler that seems very unusual and clever (not mine).  I would be very interested to know if it actually performs batter than simple series of baffles, as found on a Marauder, for example.  I am not sure the air can get into that organic foam lattice fast enough to be effective.
 
The pores seem just over 1 mm across (scaled from layer height).  I assume the pores could be made larger if they are too tight.  I suspect this device might have the pores near the central channel clog with dust pretty fast, and that cleaning it might be a challenge: 

[jackssmirkingrevenge]

1. Air flowing over a ball from a conical or spherical seat, is notorious for drawing the ball back onto the seat, rather than pushing the ball out of the way, due to the Bernoulli Principle

2. Making ports in the barrel is not going to be popular, as removing burrs on the inside would be difficult; and the reduction in bend strength undesirable.   I would set a goal that no stock parts be modified for any new invention, unless you manufacture the whole system.

Both very good points, a device that will screw on is a more pragmatic choice.

Below is an airgun muffler that seems very unusual and clever (not mine).  I would be very interested to know if it actually performs batter than simple series of baffles, as found on a Marauder, for example.  I am not sure the air can get into that organic foam lattice fast enough to be effective.
 
The pores seem just over 1 mm across (scaled from layer height).  I assume the pores could be made larger if they are too tight.  I suspect this device might have the pores near the central channel clog with dust pretty fast, and that cleaning it might be a challenge 

Interesting, to me this has always been counterintuitive to a degree, in the sense that the air should take the path of least resistance and here you're slowing it down as it attempts to fill the volume, so presumably it would do so at a lower rate.

I can understand this style of device used in commercial pneumatics where there is no muzzle hole for the gas to escape or outer casing:




I don't see it making too much of a difference in a design that also allows a projectile to go through.

That said given, the wonders of 3D design and printing, what if that lattice on a micro level had a wedge-shaped cross section where air can flow easily past it in one direction but not the other...

[subscriber]

Jack,

A few days ago I experimented with different ways of modeling "foam", as shown above.  To generate a 1.5" diameter by 6" long "slug" of foam, using different ways to model it in Solidworks, used up of 50 and 80 Mbytes as a Solidworks files, and much more as an STL.   That bogged my PC down to the point that the lack of processing speed frustrated me, and I gave up. 

The guy printing those foam filled LDCs is using one of the infill options of a particular 3D print slicer, so that very bit efficient.  I include images of my more "open cell" foam, where the filaments are 1 mm in diameter for the basket weave.  On the spherical pocket version, the pocket diameter is 3 mm, with the each hole at the connection is 1.5 mm. 

Anyway, I am dubious about the ability of such small air paths to accept air as fast as it needs to happen for LDC application.   If the foam was just a 4 mm thick layer on the inside of the outer tube to reduce pressure wave reflection, then I would be OK with it.  My basket weave idea is such a sleeve, that is both low reflection, with the ability to pass some air to a secondary space, if desired.

Anyway, have defaulted back to using a matrix of round holes in the 2 to 3 mm diameter range, that have a 0.5 mm fillet on the high pressure side, with the opposite side edges left "sharp" for more resistance to return flow.   As used here, for example:

https://www.gatewaytoairguns.org/GTA/index.php/topic,210109.0.html

[jackssmirkingrevenge]

The guy printing those foam filled LDCs is using one of the infill options of a particular 3D print slicer, so that very bit efficient.

That's quite clever, but of course it wouldn't be optimized for ideal airflow interference.

My basket weave idea is such a sleeve, that is both low reflection, with the ability to pass some air to a secondary space, if desired.

What I was suggesting was something like the basket weave but instead of having a round cross-section, something more like an arrowhead pointing towards the centerline.



I'm not sure how much of a difference it would make in practice, but it would in theory encourage flow in one direction more than the other.

Those offset designs for the Huben look great by the way!  A good way of maximizing volume without too much bulk.

That leads me to mention another harebrained notion, what if you connected a hollow plastic stock to the moderator with a length of tubing to give a lot of volume with little extra bulk 

[subscriber]

Jack,

O like your arrowhead filament section idea as a concept.   With two points to ponder:

There is a limit to how small sharp features can be generated. 

Printer mechanisms hate repetitive sharp features because of the jerky motion.  So, I generally try to round all transitions to at least 0.5 mm radius.  Sometimes Solidworks can't fit in a fillet into a complex shape, unless I reduce it to .25 mm.

That said, your triangular shape could be implemented at a scale where it makes sense, as a differential flow resistance shape.  I think if the triangle section was 2 mm long at the longest segment the idea could work.  I would model it now; except I have a request for Taipan inserts - part design in process.

If you connected an LDC to a hollow stock, through a short fat pipe, I can see it adding volume equivalent to the rear volume of a shroud.  A connecting pipe that is long and skinny wont flow enough air in the amount of time that matters.  Somewhere between 1/100 and 1/10 second.

[subscriber]

That printed "foam" in the pictures above is made by using the "gyroid" infill pattern:

At the scale of the infill pattern in the video below, that might even be useful for mufflers.  I don't know how one demarcates which areas get infill, and which do not.  But, may have found some videos about that, below:









Infill strength test showing different options:

[jackssmirkingrevenge]

That said, your triangular shape could be implemented at a scale where it makes sense, as a differential flow resistance shape.  I think if the triangle section was 2 mm long at the longest segment the idea could work

Yes it would have to be a bigger scale and good point about FDM printers not liking that sort of pattern.  I have access to SLS printers that wouldn't mind that as much, but alas contrivances designed to dampened sound are a no-no in my part of the world so my interest in the subject is purely academic.   

If you connected an LDC to a hollow stock, through a short fat pipe, I can see it adding volume equivalent to the rear volume of a shroud.  A connecting pipe that is long and skinny wont flow enough air in the amount of time that matters.  Somewhere between 1/100 and 1/10 second.

I'm picturing something like that feeding directly into the forend of a conventional stock:



It would look a little odd and need a specifically designed stock, as drawn it would also interfere with filling etc. but it's an interesting line of thought to have a massive volume without adding too much length and bulk.

That printed "foam" in the pictures above is made by using the "gyroid" infill pattern

That's a great find, it looks like it would absolutely confuse the trousers off the airflow!



 It would be really interesting to see how a tube filled with this pattern would perform compared to conventional baffles.

[subscriber]

Here, the lower "barrel" is an expended air receptacle:
https://www.pyramydair.com/product/stoeger-xm1-s4-suppressor-pcp-air-rifle-black?m=5321

[jackssmirkingrevenge]

Here, the lower "barrel" is an expended air receptacle

Something like that, and it doesn't have to look too awkward either, simply to show the aesthetics this offering from Ruger is rather handsome:

[naptemp]

This was the most interesting thread I read here in months.

[oldpro]

This was the most interesting thread I read here in months.

Though I don't get on much due to my work load I totally agree.

[subscriber]

I was wondering, Travis, if you printed and tested that short fat design you asked for?  Your results and impressions would be interesting.