(5/6/19 update) Moderator Design, Testing, and Evaluation (the big test)

Many questions. Alrighty, let me see if I can answer them. 

How does it work? Subjectively, to my ear anyway, it works very well taking the bark off the Crown. It also has good tone, not producing the shrill sounds of some silencer designs. That said, I don't have anything directly to compare it to. In a long long time ago in a galaxy far far away I was actually an engineer doing design work on firearm silencers for a company. Experience tells me small differences in both design and host can make big differences in sound, but also that the human ear is a pretty bad judge of sound intensity. My closest comparison is a mostly foam filled moderator of the same diameter and roughly the same length on my Air Arms S510. To my ear and with a sound reflective surface in front of me to send some muzzle sound back, disclaimer now stated, it sounds quieter than that. It isn't a fair comparison by any means, but it is what I have. 

I don't have a DonnyFL or Hugget, but quite frankly it isn't really that interesting to me to compare it to one. Both of those designs use pretty simple architecture, a chamber or two and some high surface area material like a wool or foam. Small differences in the material of the can and design of the caps could make them meter very differently (for better or for worse), not to mention overall size. My plan therefore is to build another suppressor design of a style similar to the felt/foam filled ones. I also want to try out a common firearms industry suppressor design, the clipped conical baffle. All of this to see if the gas diode concept has merit in this application. That is what I'm genuinely curious about. I've wanted to try it out for years, and now I finally can. It'll take me some time, but once I have all the different suppressor designs I want to compare it to, I'll dig up the old impulse sound meter, which can actually accurately compare things like gunshots unlike my ear, and quantify it. 

What is it made of? The tube is obviously carbon fiber. The core is 3D printed from ABS. I've printed other moderator designs from this, and it works great probably due in part to ABS' good impact resistance. I realize I posted the images in black and white, but I did the core on this one out of a metallic copper ABS with blue glow in the dark accents. I could do polycarbonate, an extreme PC alloy, 20% carbon filled nylon or polycarb, etc but I've never found in necessary on an airgun. *shrug* 


Fascinating. Thanks for sharing. How is the sound reduction? What is it made of? 

Wow that looks amazing! So nice to see some innovative thinking in silencers. Usually they're basically all hair curlers and washer baffles

How's the sound reduction? What you were hoping for? Better?

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That last one really is a great way to parse the question, and I want to hover over that for a second. Expectations matter. This moderator is smaller than a DonnyFL tanto. A whisker larger diameter, and about half an inch shorter. It is also half the weight. These things matter because volume, length, and mass all work to deaden sound. I bring this up because my goal was small, light, and accurate not complete and absolute silence. Suppressor designs also are capable of generating internal cross-jetting. You can make this very aggressive to make your design quieter, however it comes at the cost of accuracy and POI shift. Pellets are extremely sensitive to it, and easy to destabilize. I suspect this is why a lot of airgun moderators often have simple designs, hair curlers and washer baffles as you put it, because if you generate too much internal turbulence or cross-jetting your accuracy will to go pot. 



I hope that answered everyone's questions. Since people seem interested, I'll keep posting updates as they come.  

stoti check your private message inbox. 

To minimize cross jetting affecting the pellet would a 1st chamber without cross jetting reduce the air pressure and air velocity so that the pellet may out run the gas turbulence in later chambers with cross jetting? I think this would be effective when used in conjunction with a shrouded barrel that the gas can be redirected to from the 1st chamber.

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Yes, which is why you often see symmetrical blast baffles, at least in firearm suppressor designs. Take the Silencerco Osprey as probably the most famous example:


It doesn't completely mitigate it, of course, but it can take the edge off. The Crown you'll note already essentially has this, as it has its own "blast baffle" inside the shroud, and then you could consider the rear face of the moderator itself a second flat blast baffle which should induce no significant asymmetric cross-flow. For reasons of stacking tolerances on the concentricity though, the integral blast baffle is probably the more effective air stripper as I'd expect it to have a tighter tolerance to the pellet. 

Brilliant - thanks for your answer

Illuminating point you made about the cross jetting. Explains things with a few silencers I've tried, that just ruin accuracy without a hint of clipping.

I'll be following your progress with great interest!

Cheers!

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Yup, been there too. Worst I can remember, airgun-wise anyway, was a cross-flow K-baffle design I purchased ages ago. Really opened up the groups substantially, to the point where you couldn't really call them groups anymore. Sort of an area-effect kind of thing. The design was also shrill as hell. 

How is the silencer doing?

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It is going. I've got the flow-through clipped-conical-baffle design done and a little initial testing. Very interesting results there. The foam/felt analogue is the only one which remains. I have it all designed, most of it printed and the carbon cut, but I still have to laser out whatever high-surface-area material I'm going to use. Since long term durability isn't an issue, it is just a test mule after all, I have some medium density open cell carbon foam I'll probably use. I've used the same stuff in other moderators I've built and it works very well at sound deadening, but unless constrained has a habit of eventually pulling itself into the pellet path. *shrug* 



The original one though, the actual gas diode concept, is still living on my gun. It has picked up a fair bit of lead dust at the basal end. It has seen a couple tins of pellets now, and still works like a champ. I'm very happy with it. 

Alright, here is where everything stands. I've got three moderators to test. They are as follows:

The tesla gas diode variant. The carbon fiber section is 112mm long, meaning the suppressor adds 120mm to the total length of the Crown. I really like shooting this design. While I haven't quantified it yet, it sounds good and despite having all these different designs on hand for testing, this is the one I shoot with for fun and keep on my gun. What can I say, the lack of POI shift and sounding good make it a winner in my book. It weighs 64 grams. 






The flow-through clipped conical baffle variant. Because of the differing length of the baffle sections, this one actually came out slightly longer adding 123mm to the overall length of the Crown. I was going to do both flow-through and conventional versions of this, however upon testing I learned that this causes about a 4MIL POI shift. This POI shift is quite repeatable, you can rotate the shroud on the Crown and watch it walk around the target in a circle. On a firearm this might be considered acceptable if it didn't detrimentally impact accuracy (I didn't shoot a statistically significant group set to test this, however groups remained <3" at 100 yards which rules out clipping and pellet destabilization), however given the the Crown's shroud rotates freely, giving the threading no predetermined alignment, being able to walk an 8MIL circle around your POA I didn't really consider acceptable so decided not to bother with a full conventional design. It is at this point that I want to mention this design shifts the POI despite having effectively THREE symmetrical blast baffles. First is the Crown's internal brake, second is the rear face of the suppressor itself, and the third is the first internal baffle which I left un-clipped to minimize POI shift. So much for that. I've long harbored the suspicion that the baffle clips cause cross-jetting in the forward-flow direction, causing it to function as its own gas-diode of sorts. Omitting them would render the design significantly neutered, so isn't really viable. Unless I have a clever idea at some point in the future, I'm going to call this baffle style dead in the water for airgun use as a result.... for the nothing my opinion is worth. It weighs 53 grams. 


And finally a variant filled with constrained carbon foam. This design I don't actually have an image of the internal architecture, as it is an assembly of longitudinal rods (to constrain the foam) connected to an internally threaded muzzle end and an identical "flow through" rear section. I never bothered to build out the assembly in CAD, and it isn't particularly clever, but of note is that it uses the same rear section as the other two designs, and the same length as the gas diode design, so is not at any sort of volume disadvantage. If anything, there being less "stuff" in it, it should have a larger internal volume per length than either of the other designs. The purpose of this foam concept is, as I've said before, to act as an analogue for the "typical" industry moderator designs which use a thin layer of foam or felt as the sound absorbing structure. There is no POI shift with this design either, unsurprisingly, and in the little shooting with it I've done it doesn't sound any quieter or louder than the other two. Of course ears are a bad judge of these sorts of things, so I'll have to wait and see. It weighs 42 grams. 





To keep the testing fair between the three, I used the same threaded section at the rear with flow-through and I've also used the same muzzle cap. You'll notice rear faces are tapered on both the muzzle cap and end section of the moderator. This is to promote concentricity between the components and the carbon section. It works well too. This is then squared off so it all mates flush, looks good, and most importantly contains air/sound. 





And that is pretty much where things stand. I've got to dig out the old impact sound meter, calibrate it, set everything up on a test stand..... and oh yeah wait for a break in the weather. Currently I've got snow and rain in the forecast, so...... yeah. Results as they come. 

Also for the people who have been messaging me asking to buy one, I can make you one now, but if I were you I'd at least wait until the sound testing to see if I'm completely full of BS and have been fooling myself this entire time. There really is no rush.