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Airgun Moderator Design, Performance, and Development - The Final Mus Test+ (part 12)

Silent Thunder Ordnance


Catch the previous episode HERE.

So there are a couple things to wrap together into this test. The first is the highly anticipated tests of the DonnyFL Emperor and Ronin. I believe I'm correct in saying that the EMP is the largest commercially produced airgun moderator out there, being substantially larger than the Huggett Magna and heavier and larger diameter, although a smidge shorter, than the Clague .30 (previously the largest moderator tested) I've put these tests below, however I'm also going to insert them into the big test so anyone looking for more info can find them all in the same place. These tests were done on the Crown .22 running 32 foot pounds, just like all the others.

The second thing is to test the final Mus revisions. This is the culmination of months of trial and failure, but finally I have a design I'm happy with so this will be generating its “final” numbers. I mentioned this before, but I've abandoned optimizing it for .22 as I just don't know how I'll ever get it to beat the Pilum, but this rev. should work great on .30 and I'll also test it on the .22 just for fairness.

The third is addressing the complaints of unfairness regarding the Clague .30, and that it ought be tested on a .30 like it was intended. I don't think these claims have a great deal of merit, that it'll suddenly change directions and be an outstanding performer when dumping almost three times as much air down the bore, but I'm prepared to give it a fair shake and a chance to shine.

Donny Emperor

Donny EMP.png

Sound – 81.0
Mass (grams) – 436.6
Volume (mm^3) – 536,804
Length (mm) – 266
Diameter (mm) – 50.69
Exit OD (mm) – 8.55


The first thing that jumped out at me about this wasn't the size, it was the weight. In fact it was so heavy, I had to pull the core out and weigh it in parts as it was maxing out my scale. For those who don't speak metric, that is a whisker shy of a pound. It also is the only thing I've yet tested which is heavier than the Clague, and although it has a larger bounding volume it is a little shorter. Internally this, and the Ronin, differ from the other Donnys I've handled in that, instead of three chambers of varying sizes and two baffles, these have multiple chambers of identical size and far more of them. The Emperor also now has wire mesh around the outside of the felt as well, and it is held closed with zip-ties rather than the usual black masking tape. There also appears to now be not-insubstantial space between the outside of the core-wrap and the tube, effectively creating a permeable barrier between the inner core and an outer chamber of sorts. It may seem like a small detail, but this could have a substantial impact on ultimate performance, causing these designs to perform much better than their diameter would suggest. Fit and finish is otherwise identical to the other Donnys, as described above.

Before I leap into testing, I want to note that this Emperor was marketed and sold for .22/.25, but Donny said these came out a little on the snug side for .25 so really it is best as a .22 can. This is probably because, with a couple stacked tolerances and such a long mod to amplify any tolerance issues, you want that size exit hole to quite large to reliably clear a .22 pellet. The point I'm trying to get at though is that this was very much NOT made for .30.

My initial reaction to this design was surprise, and in a good way. Given all my testing with large diameter designs, I was expecting this to be much much louder than it actually sounded. Maybe it sounded a bit like a Huggett Belita but without the ring of the Huggett? What I'm getting at is, if you didn't know it was an enormous moderator, you'd never guess it by listening to it. It didn't seem to have that sound of very high peak and low subsequent sound you (or rather I) expect from a large diameter can. Another thing I want to note here is that the muzzle is substantially farther from the shooter's ear than with other designs, and the face is much wider, so it is possible some sound attenuation to the shooters ear occurs based simply on the form factor. Put another way, this can moves the “muzzle” of your gun almost a foot further away from your ear than no moderator, and then casts a significant shadow. Given that your muzzle may have only been two feet away from your ear to start with, this is likely not inconsequential.

So how did it actually do? Not bad really. Again I was expecting armageddon, something up in the Clague range of mid hundreds. To be below 100 was great, in fact this design was almost as good as normal sized moderators. Looking at the traces, there is clearly less residual sound than many other smaller designs, but it isn't dead silent either. It is enough that, if you were to measure with an unsuitable sound meter or a phone, you might get erroneous numbers suggesting it is quieter than say a 0dB. Given this design's length and weight I can't exactly call this result great, being almost as good as a design a quarter its mass, but it sure is a heck of a lot better than I'd have guessed.

Donny Ronin


Sound – 103.6
Mass (grams) – 267.7
Volume (mm^3) – 325,562
Length (mm) – 160.5
Diameter (mm) – 50.82
Exit OD (mm) – 8.11


I covered above, on the Emperor, the internal and aesthetic observations of these two. Beyond that, they are largely similar to the other Donny designs I've tested from an aesthetic perspective and are covered in greater detail above.

I also want to note that this design was sold for .22/.25, not .30. I too would expect this exit OD to be too tight for .30.

My subjective impression on how this design sounded was “peaky,” that is to say producing a peak which is much higher than you'd expect given its draining sound. That isn't to say it sounded quiet, because it really didn't, but having passed my initial surprise given the performance of the Emperor I guess this sounded neither luxuriously quiet nor ostentatiously loud. It definitely has the kind of sound delivery which would make it hard for an untrained ear to judge how loud it actually is, if that makes any kind of sense. I do worry I've listened to too many moderators at this point, and so my subjective impressions are starting to diverge substantially form what a lay-person would perceive, however this is why hard data exists.

Well, for those who say this sounded quieter than the Sumo, I believe them because it is..... barely. We're probably within margin of error here, but on a previous day the Sumo averaged 108 and the Ronin averaged 103.6. Of course both of these are substantially louder than smaller diameter designs, but there it is. I suspect, although could easily be wrong as I have been so many times before, the design alterations of the Ronin will give it a further edge over the Sumo on higher flow guns.

As a small aside to these two Donny tests, I expect someone will point out that, while these designs may have been bored for small-calibers, they were intended for higher power air handling. To this end I screwed them to my Crown .30 (80 foot pounds) and ran some dry-fire shots through them. The results were erratic, but far from flattering, producing the highest peak of the session at 220. I wouldn't read into that though, because I also ran a couple other designs dry for the purposes of comparison and discovered that dryfires cause moderators to behave very strangely. In short, a dryfire test of a given moderator may or may not be representative of its performance with projectile, and you'll have no way of knowing until you test it properly. :/


Mus on FX Crown .22 pushing 32 foot pounds

Mus on FX Crown .22 pushing 32 foot pounds

Mus on FX Crown .30 pushing 80 foot pounds

Mus on FX Crown .30 pushing 80 foot pounds

Sound – 78.8 (80 foot pound .30 cal Crown VP), 82.0 (32 foot pound .22 cal Crown)
Mass (grams) – 120
Volume (mm^3) – 333,794
Length (mm) – 170
Diameter (mm) – 50
Exit OD (mm) – 8.4

I just can't tell you how happy I am to have reached this point. I keep harping on it, but really this Mus design was one hell of a slog. From my original test back in March, I've been pounding my head on this wall trying to figure out why large diameter designs don't work well, and how to overcome it. I haven't figured out the former, but at least for higher power guns I've cracked the latter. Good riddance. :P As I noted in my penultimate Mus test, this winding path ultimately lead me to a concentric chamber design. A compound blast baffle deflects the majority of the initial flow and pressure to a pressure reservoir. This then slowly feeds the gas diodes which further delay the flow. Finally the dampers provide the final sound attenuation before exiting the muzzle. The only other thing I want to draw attention to about the design is that I took great pains to keep it light weight to maintain the rifle's balance and minimize POI shift. Physically it is very large, 170mm long and 50mm in diameter, but it only weighs 120 grams or 4.2 ounces. If you read my comments on the Trident and why I liked it so much, you'll notice I really put a premium on weight, especially when hung out there on the end of my barrel.

As far as performance goes, I think it performed well. It isn't quite as much of an advantage over the Pilum QD as I'd have liked on the .30, but it does sound noticeably better. Some of that is down to the quieter draining sound, there is just less noise post-peak going on here. In a weird way you can think of this design as basically a longer moderator which got smushed and so the initial sections were pushed to the outside which make room for more sound damping toward the muzzle end. It is rather giggle-worthy to shoot something this powerful and have it be this quiet. On the .22 it is noticeably louder than what I usually run, a Pilum DD, but not outrageously so. In both cases you can see the trace has a lot less going on after the peak than both Pilum designs it is “competing” with.

Beyond that I guess I don't know what to say other than that I'm just so relieved it is over. Somehow this one started losing some of the elements of fun and became a bit of a slog. So, for now anyway, I think I'm probably going to take some time to step back from airgun silencer design. After all the point of this is fun, and so when it stops being fun you ought take a break. At some point though, there is one more thing I want to specifically “debunk” which is the all-to-common-refrain of “loudest part of the gun is the hammer slap.” This might be true for the shooter, but if so it is only because your face is inches from the hammer and feet from the muzzle; measured at an equal distance the muzzle sound is definitively louder and I want to do some testing to, not just show it, but quantify it. Remember sound attenuates substantially with distance, doubling it will cut 6dB. It'd also be cool to see just how loud the target impacts are with various calibers and backstops as compared to the gun itself going off given, say, a range of 75 yards.

Performance summary for all moderator designs tested to date.


Clague .30 on the Crown .30cal running 80 foot pounds – 115.6 – Note that this trace is on a different scale than the above. Color me surprised though, the Clague DID meter substantially better with a bigger slug running down its bore but....... there is a HUGE, round, face-swallowing but to that: it sounded like a cross between star wars blaster firing and high tension steel cable breaking. It'd be freaking awesome if it were intentional, and not trying to be quiet, but it is and so I'd call it flat out unacceptable. Appalling might be another word for it, it sounds like a bad silencer sound-effect from a Hollywood movie. The only other design which resonated this badly was the unbranded moderator which I believe was from Wolf. (the manufacturer was unclear, I don't want to throw Wolf under the bus here) I almost want to shoot a video of this to show to people, as it is so weird and distinctive. I did wonder if this sound might be caused by some sort of pellet-baffle interaction, and so I tried a few dryfires through it..... nope, still resonates. It is just so weird, I don't know what else to say. So for the people who thought the .22 test was not representative of the Clauge, I hope this addresses your complaints? :/