.30cal Silencer ("Moderator") — 3D-printed — 90FPE

[subscriber]

By the way, there is no taper over the rib OD. The images that appear that way are "perspective" images. They are supposed to look more real, because the standard image can look tapered the other way on long slender objects.

There is a taper in the wall thickness under the ribs. Thickest at the first expansion chamber; then stepping down with a gentle taper to the front, where less strength is required.

 

[subscriber]

Just in case someone wanted this .30 muffler with a 1/2 - 20 thread, I have also generated such a file version (see last three images below). The thread should be usable off the printer. I have assumed the thread will print 0.3 mm undersize in diameter, and added equivalent compensation in CAD.

I have combined the STL files for the 1/2-20 and 5/8-11 thread adaptor muffler versions in one zip file, and attached them here, with combined images. I will edit or delete the post I made to the Huben muffler thread by mistake.

One version of this muffler has a printed thread designed to receive this 5/8" -11 Grainger thread insert: https://www.grainger.com/product/E-Z-LOK-Self-Locking-Thread-Insert-4ZB92

Based on the insert's dimensions and shape, as seen in the CAD model downloaded from Granger, I had to increase the ID of the printed thread significantly to avoid fouling. See images of the installed insert in my CAD model. If the insert you are planning to use is different, or has a different thread than 5/8 - 11, please advise.

Most of the images were captured before I adjusted the printed thread ID in my CAD model.

Apart from adding the thread, I increased the outside wall thickness of the second, third and fourth baffle chambers very slightly. The weight has gone up a small amount - see image with Solidworks mass calculation for ABS material.

I trust this muffler will "take the edge off", when it comes to noise. If you wanted something closer to backyard friendly, I think it would need to be at least a foot long, at this power level. It would not need to be 2" in diameter, but length seems critical to go from hearing safe, down to backyard friendly.

Anyone who likes this muffler, may download, print, use, or sell muffler prints; without my permission. By downloading this file, the individual acknowledges that they understand, this is an experimental design, that is completely untested at the time this file was published.

It is advisable to print just the rear section of the part to test the thread fit. When happy with the print settings for the the tread, print the whole part.

The part must stand front face down on the platen, with the threads up. Else the print will fail due to a lack of a self supporting structure, when upside down. Verify that the insert will screw into the full part; remove it to apply glue to just the insert. Then screw the insert back in, just below flush with the rear of the muffler surface. And set the muffler on its base for the glue to set - so that gravity helps to keep it centered, rather than drive the insert off center. Also, so that excess glue does not drop onto the air stripper lip and potentially create a speedbump there.

View attachment Two STLs for .30 MD-LDC Half20 and FiveEights11 Thread Adaptor.zip

 

[subscriber]

TeslaToTheMoon requested some design improvement to this .30 muffler:

The rounded triangular pockets at the front end are pyramid shaped to avoid print overhangs.
I needed to add 2 mm to the front wall to emboss the pyramidal pockets. I went back and cut the front internal wall shape to take advantage by increasing the internal volume slightly.

The thread pocket has a relief cut for the insert installation tool.

STL for Rev 2 is attached in the zip file below:

View attachment STL for .30 MD LDC 52 x 130 mm for thread insert Revision2.ZIP

 

[subscriber]

Same muffler improvements as Version2 above, but with a 1/2 - 20 thread as part of the print.
The thread should be usable directly off the printer.

STL attached in ZIP file below.

View attachment STL for .30 MD LDC 52 x 130 mm Half20 Thread Version2.zip

 

[JungleShooter]

Besides the sound improvement, this silencer will be a visual improvement to any rifle.


I feel fortunate that I get to mount this on my rifle.

Matthias

 

[Mr.H]

Very interesting thread! And Mr. subscriber, how refreshing it is to see your contributions to this community!

 

[subscriber]

Very interesting thread! And Mr. subscriber, how refreshing it is to see your contributions to this community!

Thanks, Mr.H

I have done most of my damage on the GTA forum, but their maximum attachment size is 3.2 Mb. Then, someone on AGN asked me to do a custom design. It seems to have snowballed from there

 

[JungleShooter]

I have the distinct impression that if we compared GTA and AGN users — there are more PCP users on AGN (at least they are more busy with their PCPs than with the springers they probably also have stored away in some closet).

And silencers don't do much for springers — but they do wonders for PCP's.
One important reason I have left the springer world — stealth is important when living in a an anti-gun climate.

➠
So, subscriber, we are very happy that you have come to AGN — not just GTA.

Matthias

 

[bigHUN]

Do you need to push a reamer through? I don't know fdm how much melts the edges...

 

[OldSpook]

Do you need to push a reamer through? I don't know fdm how much melts the edges...

I think he is talking about a resin printer. I would not expect that to hold together long if it was run on an FDM printer, even with PETG. Could be wrong, I've printed some that have been run at 130 fpe but I always played it safe and sleeved them in CF. STO's inserts look like FDM prints from a 0.8 nozzle and his Tesla Diodes are carrying quite a bit more than 130 I believe.

Always stronger to print the threads tight and then cut them with a tap but not everyone has a tap or the skill to use it. It is pretty easy to get that tap in crooked and ruin the whole thing, especially in plastic. The tap just wants to keep going in whatever direction you started it.

 

[subscriber]

Do you need to push a reamer through? I don't know fdm how much melts the edges...

If the part was printed on its side, the baffle bores would close in to form an oval. Then reaming to a round shape of a known diameter would be a good idea.

My designs are mostly to be printed with the small end of the cones pointing straight up. FDM printing a nominal 8 mm diameter hole generally will close in that hole by around 0.3 mm - depending on the material, printer and print settings. I take typical shrinkage into account and gave up on minimum projectile clearance designs to avoid trouble.

Most of my current designs have baffle bores that are stepped, or taper wider towards the front, to be more tolerant of misalignment. Generally, I aim at baffle bores starting at 1 mm radial clearance to the projectile, on the first baffle. Then opening up radially by an additional 0.25 degree. If anyone thinks this is too loose, they are welcome to use their own strategy.

Certainly, if one printed a nominal 7 mm baffle bore all the way through, then reamed to 8 mm I would not have a problem with that, for .22 caliber. Perhaps even for .25 - assuming all other elements in the system were precise and stiff enough to reduce dynamic misalignment under vibration, as the projectile passed through.

If you are concerned about a lack of crisp baffle bore shape for a round and symmetrical air stripper, consider how some mufflers have deliberately slanting baffle bores to create turbulence. I think cross turbulence at or ahead of an airgun pellet is not a great idea for group size an placement, but results matter more than theory. I am concerned about the potential for uneven airflow in my offset muffler designs, but people as for offsets, so that is what I design for them.

Sometimes I do a "can in a can" design to try an minimize asymmetrical airflow effects. The owner of the offset reflex muffler shown below seems happy with it, but it is in .357 caliber. So a heavy projectile - see attachments. Yes, I was in a hurry so I grabbed a combined image off a screen, rather that finding the full size images. If anyone found the images I "stole" on GTA, they would notice I posted them there You need to be a member there to see the images.

So, I can tell you my design strategy, that works in conjunction with my skilled printer guys. The ones I recommend, if someone can't print their own. I can explain my strategy, but would not suggest it is the best or only strategy. Promoting the use of a tool or machine to make a printed part better assumes proper setup, and the skill to use it.

 

[subscriber]

OldSpook,

I share your preference for placing printed baffles inside a CF or aluminum tube, for greater confidence based on predictable strength. Some people do not like cutting CF tube due to concerns about fibers released getting into their eyes, lungs and skin. Or, they think that it is just too much bother.

I am willing to design fully printed mufflers for them, provided they realize and accept that there is a potential durability problem; with some risk of frag.

Nominally, PETG has 1/6 the tensile yield strength of 6061-T6 aluminum. Because FDM printing can have dodgy layer adhesion, I de-rate that to 1/12. Usually I take my designs and thin the walls so that the weakened version can be used as a proof test for the full strength version. With what I have posted on AGN, those steps are being skipped because the "customers" want one-and-done designs. So, I go "heavy", based on extrapolated results from what I have done for other customers.

How much wall thickness is prudent for a muffler depends on more than FPE. If we are taking cylindrical baffle chambers, doubling the ID for a given wall thickness and length (for that chamber), has the volume quadruple. This, while the ability of the wall to stand air pressure drops by a factor of two. So, making the chamber smaller in diameter for a given wall thickness, increases the pressure rating by the same factor; while the internal volume is reduced by a factor of four, thus increasing the bulk pressure by a factor of four. Providing one understands this, the volume can be adjusted by making the chamber longer.

Rather than a larger caliber of a given FPE increasing the risk of blowing a given muffler design, if only the baffle bores are increased then there is more "safety valve" effect due to more leakage from the central bore. So, larger caliber mufflers are safer at a given power level, than the same overall design for smaller calibers, at the that power level.

Any fully printed muffler that does not rupture at the wall in the first chamber after the barrel muzzle, at a given wall thickness, means the walls ahead of that chamber can be made thinner. Simply because the chambers do not all work equally hard. Not to resist pressure, impact, or bending moment. So, I make the outer wall and baffles of the first chamber much thicker than the last chamber. This is done to protect the first chamber, and to avoid adding forward weight that does nothing to reduce failure risk.

A stiff CF or aluminum outer tube is not only stronger than integrally printing the tube, but for long mufflers, adds droop resistance. Plastics "creep" under steady loads, even at "room temperature", unless the material contains a filler such as glass fiber. At elevated temperature from direct sunlight, the rate and risk of plastic creep goes up. So, a completely printed muffler that is long for its diameter, and that uses a very tight bore, may eventually clip near the front end. It may even be possible that a slender printed muffler may whip around to cause clipping, where one wrapped in a CF or metal tube would resist that better.

There is plastic filament for DSM printing, that contains CF. I do not know what percentage and length fiber these printing filaments contain, but potentially, that might be an answer to some of the strength and stability limitations of "naked" printed mufflers. Assuming good layer adhesion....

I share your preference for printing threaded holes undersize, and then chasing with a tap. A lot of people printing my designs want the part to screw on, directly off the printer. I have no control over their material, printer and settings; so then I design such threads as if my printer guy will be making the part. Ohers can then calibrate their X and Y axis, if the diameter is too tight or too loose.

 

[BlackICE]

If the part was printed on its side, the baffle bores would close in to form an oval. Then reaming to a round shape of a known diameter would be a good idea.

My designs are mostly to be printed with the small end of the cones pointing straight up. FDM printing a nominal 8 mm diameter hole generally will close in that hole by around 0.3 mm - depending on the material, printer and print settings. I take typical shrinkage into account and gave up on minimum projectile clearance designs to avoid trouble.

Most of my current designs have baffle bores that are stepped, or taper wider towards the front, to be more tolerant of misalignment. Generally, I aim at baffle bores starting at 1 mm radial clearance to the projectile, on the first baffle. Then opening up radially by an additional 0.25 degree. If anyone thinks this is too loose, they are welcome to use their own strategy.

Certainly, if one printed a nominal 7 mm baffle bore all the way through, then reamed to 8 mm I would not have a problem with that, for .22 caliber. Perhaps even for .25 - assuming all other elements in the system were precise and stiff enough to reduce dynamic misalignment under vibration, as the projectile passed through.

If you are concerned about a lack of crisp baffle bore shape for a round and symmetrical air stripper, consider how some mufflers have deliberately slanting baffle bores to create turbulence. I think cross turbulence at or ahead of an airgun pellet is not a great idea for group size an placement, but results matter more than theory. I am concerned about the potential for uneven airflow in my offset muffler designs, but people as for offsets, so that is what I design for them.

Sometimes I do a "can in a can" design to try an minimize asymmetrical airflow effects. The owner of the offset reflex muffler shown below seems happy with it, but it is in .357 caliber. So a heavy projectile - see attachments. Yes, I was in a hurry so I grabbed a combined image off a screen, rather that finding the full size images. If anyone found the images I "stole" on GTA, they would notice I posted them there You need to be a member there to see the images.

So, I can tell you my design strategy, that works in conjunction with my skilled printer guys. The ones I recommend, if someone can't print their own. I can explain my strategy, but would not suggest it is the best or only strategy. Promoting the use of a tool or machine to make a printed part better assumes proper setup, and the skill to use it.

View attachment 390334

View attachment 390335

Instead of symmetrical baffles and an offset chamber, how about asymmetrical baffles with the exception of the 1st baffle have "symmetrical" flow characteristics. That's what Edgun does and it seems to work well.

 

[subscriber]

BlackICE,

Anything that performs well cannot be "wrong". I think Edgun is assuming (correctly) that the first air stripper is keeping most of the air behind the pellet, where turbulence can't hurt it.

To efficiency of the first air stripper depends on the rest of the system. Starting with the shape of the air stripper, its stand-off distance from the muzzle, and its bore to projectile clearance.

 

[subscriber]

Strength and creep resistance are not the same thing:

 

[subscriber]

 

[BlackICE]

BlackICE,

Anything that performs well cannot be "wrong". I think Edgun is assuming (correctly) that the first air stripper is keeping most of the air behind the pellet, where turbulence can't hurt it.

To efficiency of the first air stripper depends on the rest of the system. Starting with the shape of the air stripper, its stand-off distance from the muzzle, and its bore to projectile clearance.

The baffles work well, but adding foam to the shroud did wonders. The 1st baffle is at the bottom. I think it can be improved by using cones rather than just sloped angles. That design was limited by a shape that can be molded.

 

[BlackICE]

OldSpook,

I share your preference for placing printed baffles inside a CF or aluminum tube, for greater confidence based on predictable strength. Some people do not like cutting CF tube due to concerns about fibers released getting into their eyes, lungs and skin. Or, they think that it is just too much bother.

I found a way to work with CF tubes that I think is safe. I work outside where the wind will blow the stuff away from me. Wear an N95 mask and face shield. Rough cut with an angle grinder with abrasive wheel. Finish to size with 3d printed sanding fixtures. CF sure save a lot of weight. I replaced my Vixen's aluminum shroud with CF and added a 3d printed baffle. Lighter and much quieter. The Vixen baffles and shroud do very little to quiet it down.

 

[subscriber]

Wet cutting and sanding are also an option to control the dust. Then rinsing off the residue.

 

[subscriber]

Mike in TX on GTA has started printing Matthias .30 muffler (subject of this thread). Yes, he chose to do 50% infill, but the outside appearance of the deep waffle pattern is what I want to show: