Catch the previous episode HERE.

There is a lot to cover here, the formal introduction of the Sarissa though some variants have been available for some time, the introduction of a new test platform and the journey that took, and the announcement of Silent Thunder Ordnance picking up airgun related products thus making my pokey little adventures in airgun moderator and accessory design that little bit more formal.

An acoustic excerpt

Before launching into the primary content of this blog post, I wanted to share an excerpt from another blog I’d been reading. I bang on and on about how subjective the ear is, and how sustained sounds are perceived as louder than they really are. While there are a lot of interesting phenomena here, one in particular jumped out at me as relevant to my reader’s (your) potential interest. It is a simple plain-English explanation of some of the mechanics behind impulse sound in the human ear:

“As mentioned in the introduction, when confronted with a high-intensity stimulus, the middle ear muscles involuntarily contract. This decreases the amount of vibrational energy that transfers to the sensitive cochlea, which converts sonic vibrations into electrical impulses for processing by the brain. Basically, the muscles close to protect the more sensitive structures of the ear.

The brain interprets the dynamic signature of these reduced-loudness sounds, with the initial loud transient followed by immediate reduction when the ear muscles respond. The result? It still senses ‘loud sustained noise’.” - (ref. output.com/blog/9-sound-design-tips-to-hack-your-listeners-ears)

For those interested, I would of course encourage reading the entire post, acoustics is both a fascinating and bottomless subject.

Officially launching airgun products

Silent Thunder Ordnance officially is offering airgun products. For the time being moderators remain experimental and in their own special place, however that hasn’t stopped us from bringing a few little whizz-bangs to market which might make people’s airgunning-lives better. For a start, all the digital design files available for free download are now visible and easy to find from the main website. They will remain free, available, and hopefully useful to the community. We ask only that they not be re-hosted, as the designs will be updated, modified, and added to over time, simply link back to the source here where they will ALWAYS be free to download.

The shroud depinger is, so far, the only acoustic experiment from airgunning land that has made it out into the wild. This deceptively simple and vastly underrated item simply prevents sound resonating in the shroud of your airgun, improving sound signature. In some cases the results are subtle, in others pronounced, but given that it only costs a couple bucks, is easy to install, and weighs practically nothing we use them like bacon; put it on EVERYTHING!

Finally is the pellet baffle. There is something of an unending quest to try and find a better way to carry pellets. And all the requirements are contradictory. You want them to be secure, but quickly and easily accessible. You want it to be compact, but contain many rounds. You want it to be cheap, but you want it to be good. And, most importantly, you do not want your pellets to be damaged by banging into each other or the sides of the tin. Meanwhile, we’ve all got stacks and stacks of JSB pellet tins. These tins, somewhat unusually, contain foam padding on the top and bottom. This is great for keeping the pellets safe when the tin is full. Trouble is, as the tin starts to empty, pellets can slosh around from side to side. Every time you turn the tin on its side, some pellet falls the almost 100mm (roughly 4”) from what is now the “top” to either the bare metal edge or some other unfortunate pellet below it. There has to be a better way right? Enter the pellet baffle. It drops into your standard JSB pellet tin, no fuss, and has four separate compartments which keep the pellets separate from each other and from the walls of the tin. Consume them one at a time, keeping pellets firmly packed so they don’t bang into each other until they’re used, and even once there is “space to slosh” the distance one can travel is much shorter and any impacts cushioned. Each baffle is made of the same sort of foam used in premium cases for guns, electronics, instrumentation, really anything you take into the field. Simple, effective, cheap.

All this thinking about, and testing of, pellet containers has lead to some interesting ideas for an “ultimate pellet tin,” which if people have input on we’d love to hear. For now though, we’ve got some ideas and are experimenting with some designs. What will become of it is hard to say, but just maybe we’ll be able to roll out a better mousetrap for carrying pellets.

A more powerful test platform (or higher flow factor at least)

It has become increasingly clear that the FX Crown .30 isn’t what I initially thought it was, which is to say it doesn’t represent the “upper bound” of “reasonable power” for the “majority of airguns” at least as far as a moderator is concerned. Some of this is simply down to an unexpected surge in the popularity of slugs. Some of this is down to FX’s pioneering research into barrels and airgun modularity. And some of this is down to the Crown .30 just being too damn efficient and having too generous and effective a shroud. What then can serve the role of a higher flow factor test platform?

There are lots of options, but relatively few great ones. Lets eliminate the obvious: the Airforce Texan is out. Why? Lots of reasons actually, but chief among them is that the platform is unregulated. This means that, like the AAA Slayer, even though some shots have consistent velocity every single shot meters different. Okay so it needs to be regulated, and not just regulated, but have a nice consistent regulator. As I follow a lot of subtle trends, chipping away a few points with a little tweak here or there, shot-to-shot inconsistency requires large sample sizes which are wasteful and time consuming to generate. That leads to another obvious option: the FX Impact. Now I’m getting nitpicky, but they’re awfully expensive, and in my opinion have just crossed over to the wrong side of the mechanical complexity/elegance line. They’re also so popular it is hard to get your hands on one at the moment.

Alright so consistent regulator, high(er) flow factor, preferably not super expensive, good air supply, modular (snuck that one in there), and available. How about an FX Dreamline with a few mods? Perfect! The astute will cry that the Dreamline is no more powerful than the Crown, and that is oh so true, but the story doesn’t end there. The Dreamline can easily accept an effectively unlimited number of plenum extensions. That is handy. It also, unlike the new “ultralight” barrel Crowns, can readily have its shroud removed and take a direct mount moderator with no modification. For those paying attention to flow factor, this alone provides a big boost in the amount of air being served up hot and fresh to the mod.

And there is one final twist here: the Dreamline is a popular, instead of just throwing all this together and seeing where I end up, the plan is to incrementally increase performance, carefully documenting things along the way, to help out the next guy who may be interested in replicating at least some of the work done here.

The factory tuned FX Dreamline

Dreamline Factory Configuration:
75FPE w/ JSB 50.15g pellets shooting avg. 820fps. Flow Factor w/out shroud 5690. Flow factor w/ shroud 2370 assuming a shroud factor of 2.5. (flow factor w/ hypothetical Crown shroud would be 948 for the sake of comparison) This shows the Dreamline more or less doing exactly what you’d expect, it is a little less powerful than the Crown .30 in factory configuration and uses a correspondingly smaller amount of air.

This rifle is also loud, PROPERLY loud, no surprise it ships with a moderator as standard as you’ll see below. Something of note here though is it shipped with a DonnyFX with an 8mm bore. That seems awfully snug for a .30 to me, less than 0.2mm clearance between pellet and moderator bore. By comparison, the minimum clearance I’d recommend for a .30 is 8.4mm which provides TWICE the bore clearance. No surprise then the Donny came clipping too. These are all advertised as coming with DonnyFX moderators, I think someone just put the wrong one on. Since it is how the rifle came though, and came loctited on I might add, I figured I may as well make hay and test it in factory configuration. I should add here quickly that, while the gas diode technology I use is, by design, relatively bore agnostic, the same can not be said for more conventional designs like the Donny; acoustic performance is very likely improved by this snug bore.

I want to note quickly that, as per usual, all these traces are not to scale!

FX Dream .30 factory tune shrouded w/ Donny FX (clipping) FULL FACTORY CONFIG AS-SHIPPED - 189.0
This is not quiet, no two ways about it, but admirable given the circumstances. I guess the best way to put it is that this is substantially quieter than the Crown .30 in factory configuration with its shroud extended, but you’d never mistake it for anything other than a powerful airgun by listening to it. It is quite a sustained sound, as you can see from the trace below. The peak is not an uncorking sound, but the moderator “whistling” as air tirades through it. This contributes substantially to the subjective perception of loudness.

Dream factory tune shroud donny as-shipped.png

So that is great and all, but what is it a reduction from? How much work is that mod really doing? What does the gun meter with no moderator? Well step one was getting it off, a not-insubstantial challenge given the red loctite holding it on, but far from impossible. I also wanted to pull the shroud, a much easier task, to increase the flow-factor, and see just what sort of violence this thing is capable of.

FX Dream .30 factory tune shroud only - 1,754.9
Normally I only see readings in this range testing firearm suppressors. It is loud. I wore hearing protection and was glad for it. You can see here that the shroud, particularly without a moderator, isn’t holding terribly much pressure as the trace tapers very quickly. Still better than nothing right?

FX Dream .30 factory tune no-shroud (bare muzzle) - 2,578.0
This is quieter than most un-suppressed firearms, but certainly not all. I’m not sure what I was expecting. I suspect that random peak all alone on the right hand side of the long-view trace is the sound reflecting off something. Note it is in the trace above as well.

FX Dream .30 factory tune no-shroud w/ Donny FX (clipping) - 370.0
I figured while I had it on hand I’d throw the Donny on in this configuration as well. This is louder, no surprise. To give you a little context, as the scale I use is non-linear, this is equivalent to more than doubling the distance between yourself and the sound source. So, even though the dreamline’s shroud is tiny, removing it and using this DonnyFX mod in both cases is the difference between the hearing the gun at over 100 meters to hearing the gun at 50 meters. It is a great illustration of why the shroud factor is so important to calculating flow factor, even the teenie-weenie shroud in the Dreamline, most of which is full of barrel sleeve anyway, makes a HUGE difference.

Dream factory tune no shroud DonnyFX.png

The point of this rig though is to develop higher flow variants of the Sarissa and potentially Falx. To do this I would like a bit more, and the Dreamline will not remain in factory configuration. Power and flow will necessarily increase, “invalidating” all of these tests for future comparisons. As a result I’ll breeze over a lot of the experiments I did pre-modification, but wanted to throw the two obvious ones out, the experimental high flow Sarissa and the moderate flow Falx. To be clear, the latter wasn’t meant for this, but I was curious how it’d perform. Everything I’ve learned about this diode technology so far suggests that, as guns get more powerful, it will become more effective relatively speaking. After all, it is fundamentally based on a feedback loop whereby the more air you dump into them, the more they are able to push back.

FX Dream .30 factory tune no-shroud moderate flow Falx - 124.3
I was pleasantly surprised by the result, especially as it is about five times the flow factor it was tuned for. It wasn’t particularly loud or whistle-y. It is a testament to the improvements of the rev.2 design’s diodes specifically. You wouldn’t mistake it for a moderated .22 at 30FPE, but It makes me think that a high flow variant of this design could improve this performance substantially. Less than 100 is my goal, but I’d like to achieve that on the final higher power tune of the Dreamline. I’m writing this blog post as I go, over the course of these experiments weeks if not months will have elapsed, so we’ll see down below if I manage it. As I write this though, I have no idea.

Dream Factory Tune Bare Muzzle Falx TD.png

FX Dream .30 factory tune no-shroud high flow Sarissa (experimental rev.) - 71.0
This one floored me. You really could confuse it with a 30FPE .22. Given that it is a snarling barking almost 6K flow factor .30 cal running a first-generation experimental moderator core this was the last thing I expected. Rarely do my initial moderator experiments meet with success, usually I’m a few failed experiments deep before something is really working. Maybe this means I’m actually starting to figure this stuff out? *shrug* I guess we’ll see as this rifle gets more powerful.

Power enhancement

Step one, obviously, is to add a power plenum. Step two, perhaps slightly less obviously, is a second power plenum. Why two? More bigger more better? So, hypothetically speaking, performance as plenum size increases should asymptotically approach a performance ceiling, all else remaining unchanged regarding the rifle’s tune. Practically speaking, that ceiling will resemble that of an unregulated rifle at its peak power; a “plenum” the size of the full air reservoir. The point? A little napkin math suggests that a reasonable performance increase will be observed in this rifle from the addition of a second plenum extension, and, as they’re a pretty cheap thrill, why not? There is a wrench in the works with this though, as there appears to be a choke point in the Dreamline’s plenum between the extension and the valve which is part of the valve-return assembly. So we’ll have to see how this all works out. Hopefully, if nothing else, it’ll provide useful information to someone else out there. I am aware that stacking multiple plenum extensions has been done already with the dreamline, but none of the writeups I could find listed gains from each additional plenum.

Original
FPS w/ 50.15 - 820
FPE w/ 50.15 - 74.9
Flow factor (calculated) - 5690

1 Power Plenum
FPS w/ 50.15 - 845
FPE w/ 50.15 - 79.53
Flow factor (estimated) - 6040
Power increase - 5.8%

2 Power Plenums
FPS w/ 50.15 - 855
FPE w/ 50.15 - 81.43
Flow factor (estimated) - 6190
Power increase - 2.3%

So a second power plenum added just shy of half the performance of the first. Not too shabby. A third might not be all that helpful though. ;) Hammer spring tension is rarely maxed out on these guns from the factory, so the next obvious step is to max that out and see where the plateau is.

2 Power Plenums HST adjust only
FPS w/ 50.15 - 865
FPE w/ 50.15 - 83.34
Flow factor (estimated) - 6335
Power increase - 2.3%

The plateau actually occurred with the HST less-than-maxed-out. So the next obvious step is to increase the reg a little bit and give the gun a final consistency/efficiency tune. At 160BAR there was still more to give from the HST, however this is the stated reg limit according to FX, so I stopped here. Keep in mind, when tuning, there is a peak where either more or less HST will reduce power. To maximize accuracy and efficiency you typically want to be roughly 5% below max power on the HST. And that is what I aimed for with this tune, because I also test my moderator designs for accuracy to ensure nothing is messing up pellet stability. So, yes, it isn’t truly “max power.”

2 Power Plenums, HST and reg tuned (160BAR)
FPS w/ 50.15 - 883
FPE w/ 50.15 - 86.85
Flow factor (calculated)- 6500
Power increase - 4.0%
Total power increase - 13.8%

And, for now, that is where I’ll leave it. If projectile velocity, rather than flow factor, were the goal, the obvious next move would be a 700mm barrel. If a higher flow factor is necessary, opening up the breathing path of the rifle, a higher pressure reg, a hammer weight, a stiffer hammer spring, and another plenum extension could all boost this rifle further, but probably not into a whole different league. For now then, I think this is where it’ll stay. It is a big jump over the .30 Crown and should allow for the development of moderators for everything short of what I’ll lump together as “big bores.” (based on advertised numbers, a Texan is something like 30,000 flow factor, which is just a different league)

The Dreamline; gently power massaged

Now to repeat most of the above tests but with the new higher power/flow configuration. As an aside, I can’t get over how smooth the dreamline's cocking action is. The throw is longer, sure, but it also feels like the leade on this barrel may be different as pellets go in effortlessly. Is this a characteristic of the new FX STX Superior liners? I digress.

FX Dream .30 power tune no-shroud (bare muzzle) - 3,668.4
This was so loud I had to bump the scale up even further. Don’t let the modesty of the trace fool you, it is just the scale, this was properly loud. Also that random secondary peak (sound reflection off something?) is once again making an appearance. At least it is consistent.

FX Dream .30 power tune no-shroud (bare muzzle) Donny FX- 448.7
This isn’t really a reasonable/fair application for this little moderator, but I wanted to include it here as a point of comparison, a before and after, outside my own wacky designs. You see the diodes can do odd things, what with their whole “blow harder and they hold harder” mode of action, and that can make it hard to get some form of context. The conventional “hair curlers and washer baffles” style, based on my experiments so far anyway, seem to be much more predictable in that, when you blow harder, they get louder. As before it sets up an oscillation inside itself whereby the uncorking event is not even close to the peak. Again, I wouldn’t have called this moderator suitable for this application. On a positive note though, I think the Donny’s tiny exterior holes/vents acts in its favor. At this power level something like a Huggett or 0dB what with those big slots I think might see substantial amounts of sound exiting from them.

FX Dream .30 power tune no-shroud (bare muzzle) Falx High Flow - 135.3
Given how well the Falx Moderate Flow did before (on the unmodified Dreamline), I made a few little tweaks to create the first high flow variant. This is the result. I’m quite pleased with it, all things considered. As with everything, I’ll keep tweaking and tuning, I think I can cut that down a bit more, but it isn’t bad by any stretch. I am definitely feeling the squeeze here though for space, I really want more room for diodes and damping. That sustained post-peak-sound is not ideal, although perhaps is inevitable given the constraints. For what its worth, I also put a moderate flow Falx on here, to an average peak of 148.2. The moderate flow really isn’t suitable for these flow levels, but it was closer than I had expected in terms of peak.

FX Dream .30 power tune no-shroud (bare muzzle) Sarissa High Flow - 107.8
So to answer my own question, no I didn’t manage less than 100. :( I’ll keep tweaking and fettling and adjusting of course, but there was an unexpected and pleasant surprise in this: the post peak sound is quite low. Sure, I failed to keep the average peak under 100, but the post peak sound has exceeded my wildest expectations. In stark contrast to before the power-tune, you wouldn’t confuse the report with the Crown .22, but if pressed you wouldn’t think it a snarling almost 90FPE unshrouded rifle either. So, for now, I’ll declare victory and wrap up this already way-too-long blog post.

I had a section here in the rough draft labeled “power tune, 3rd round.” I guess I didn’t need it. I’m trying to wrap this lengthy mess together with some unifying thoughts. I guess, thinking back a couple months when I decided to set this whole “high flow” thing in motion, I thought I’d need a bit more “context” to mentally place the performance of my moderator experiments at this higher flow factor. I still want some more context, perhaps another “The Big Test” series where I run a bunch of commercial designs, however I would never have dreamed I’d manage to get these high flow mods down close to moderate and standard flow performance figures and thus already have at least some point of reference. I especially didn’t expect to manage it so quickly. The Mus and Gladius both had difficult births, so for these to just kinda work was an unexpected surprise, but a welcome one.

As with everything I’ll keep tuning and tweaking and seeing where I can shave a few points off. But that, for now, is that. Thanks as always for reading and for all the encouragement. It may seem like a little thing, but I really appreciate it. It makes all this worthwhile. :) Until next time guys.