Airgun Moderator Design, Performance, and Development - THE BIG TEST; HIGH FLOW

A goal of the “big test” series is to provide an ongoing reference to the performance of different moderators at different flow levels. Moderators will be added and charts will be updated periodically however the majority of the text will not be. If you have a moderator you’re curious about, please feel free to get in touch, we’re happy to test it and add an entry below so everyone can benefit. The test series are linked below:

Standard flow - FX Crown .22 shrouded producing 32 foot pounds. Flow Factor 460

Moderate flow - FX Crown .30 shrouded producing 80 foot pounds. Flow Factor 1,111

High flow - FX Dreamline .30 unshrouded producing 87 foot pounds. Flow Factor 6,500

An immense thank you to everyone who has loaned a moderator for testing purposes here. This project would not be possible without you, and with your help will keep growing. So, again, thank you!

First, a brief nod to the host which is a power-modified FX Dreamline .30. The lack of a shroud significantly increases the flow factor, that is to say the air it serves to the moderator, and in turn increases the loudness substantially. More about the building of the host can be found HERE.

The test protocol

The muzzle of the moderator is exactly parallel to the pickup, and separated by exactly one meter. The milspec protocol for firearm suppressors is 1.6 meters off the ground, and that is replicated here except when there is snow on the ground, in which case the pickups are placed 1.6m above the surface of the snow. Two pickups are used, next to each other, and equidistant from the moderator. Each test was five shots. The results are an average of that, so ten datapoints. The numbers are raw output, and have not been converted to decibels. I hand select each sound profile (image) which I feel is representative of the moderator's overall performance. The host gun is as stated above. All tests were taken with the moderator directly mounted to the muzzle, with no shroud or any other reflex volume.

FX Dream .30 power tune no-shroud (bare muzzle)
Sound - 3,668.4

Don’t let the modesty of the trace fool you, it is just the scale. This was properly loud, as in there are bare-muzzle firearms which are quieter than this kind of loud. I wore hearing protection and was glad of it. As I noted before, that little spike well after the peak is likely sound reflecting back off some surface.

Donny FX
Sound – 448.7
Mass (grams) – 135.5
Volume (mm^3) – 118,941
Length (mm) – 126.5
Diameter (mm) – 34.6
Exit OD (mm) – 8.04

As I covered in a previous blog series HERE, this moderator probably isn’t really suited for this flow factor/host. That said, it came with it and there is no indication on the manufacturer’s website suggesting this innaplicability, so why not put the results here? At bare minimum, it should provide a good basis for comparison. What sort of performance would/should you expect from a small-ish moderator on a high flow gun?

It wasn’t exactly quiet, but that was to be expected. What was unexpected was that it set up an internal oscillation whereby the peak was not the uncorking event. This sustained sound contributed to the perception of loudness, and looking again could possibly have clipped the scale resulting in an erroneously low reading. To the subjective ear this was a whistle-y hiss-y sort of sound. All in all though, it was quieter than I had expected. I took my hearing protection off to listen to it for two of the shots.

Donny Emperor
Sound – 141.0
Mass (grams) – 438.2
Volume (mm^3) – 536,804
Length (mm) – 266
Diameter (mm) – 50.69
Exit OD (mm) – 9.5

The “Emperor” is the largest moderator DonnyFL offers. It also has the largest internal volume of any moderator yet tested, and has the most mass with which to absorb energy. A high flow rifle seems like the application it was made for. I should note this EMP on loan is different from the one loaned for the standard flow test. This one was recently purchased and should be, at the time of writing, the latest gen. I’m told it was sold for “.177-.30 cal” and that appears to be consistent with its bore diameter. Other than the exit bore and slight difference in mass, it appears to be identical to the other example tested.

The perception of this is not “mousefart,” there is a distinct pop followed by a whoosh. This is much more clearly perceptible from the side or near a sound-reflective-surface, than it is from the shooter’s perspective.

Clague
Sound – 148.3
Mass (grams) – 325
Volume (mm^3) – 493,214
Length (mm) – 276
Diameter (mm) – 47.7
Exit OD (mm) – 9.6

This Clague has not done well in previous tests. While I strive to keep these impersonal and unbiased, I really hoped that this would be a chance for the Clague to shine. It goes big in the length, mass, and volume department, which doesn’t always work out well for standard flow rifles. It picked up some weird resonance when tested at moderate flow levels, which may have been part of an interaction with the shroud. It is possible though that here at the higher end of flow, things could start to work out. This isn’t purely imagination or wish fulfillment either. This Clague was allegedly (I’m not the original owner) made for an FX Impact .30. Impacts tend to be a slightly lower flow factor than their Crown counterparts of equal power, but based on the shape of the cone at the rear it may have been intended for one without a shroud. While I have not found anything from Mr. Clague to suggest he tunes his designs for flow factors or equivalent, my understanding is that they are made-to-order for the customer’s requested application.

The Clague again sets up a resonance here, although to my ear it was less distinct than on the Crown. While being fairly close numerically to the Emperor, the post-peak-sound here creates the impression that it is louder but not by a huge margin, and it is both smaller and lighter. So, in that regard, I would say the Clague held its own against the EMP.

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I want to put a break here between the commercial moderators tested and my experimental moderator designs. The obvious “conflict of interest” aside, I can’t overstate the value of having both the host and test equipment on hand when working on designs. For every success or noteworthy design that ends up in the blog series, I have many MANY failures. Posting only the culmination of my work as a direct comparison is somewhat unfair, thus I wanted a break between the two, so please keep that context in mind.

Falx High Flow
Sound – 135.3
Mass (grams) – 180
Volume (mm^3) – 213,628
Length (mm) – 170
Diameter (mm) – 40
Exit OD (mm) – 8.4

While lower flow-factors taught the hard lesson that bigger isn’t universally better, at this flow factor the lack of size of the Falx is definitely a limiting-factor when it comes to performance. The peak is relatively low, all things considered, that much is good. Less good is the audible “whoosh,” the sound of the diodes draining. Without somewhere for them to store that extra air for longer, such as a shroud, it just has to come tiraiding out sooner and makes more noise doing so. Put a different way, it is surprisingly quiet for its size, but it still sounds like a powerful airgun.

Sarissa High Flow
Sound – 107.8
Mass (grams) – 260
Volume (mm^3) – 320,442
Length (mm) – 255
Diameter (mm) – 40
Exit OD (mm) – 10*

*Note this moderator runs a tapered bore, which starts at 8.4mm at the rear and opens up to 10mm at the exit to reduce the chances of clipping.

The point of the Sarissa was to take the proven concepts of the Falx, but free them from its size constraints. There is just more room, which is filled with more sound damping and an additional gas diode. Both the peak and post-peak draining are remarkably quiet for this kind of air. The hiss of the pellet moving through the air is readily apparent.

Brevitas *tested 10.29.20*
Sound – 1213.0
Mass (grams) – 30
Volume (mm^3) – 45,565
Length (mm) – 74
Diameter (mm) – 28
Exit OD (mm) – 9.0

The Brevitas was not meant for this. Without a shroud to store the backpressure being generated, there is no possible way it could perform well, and indeed it didn’t. It only seemed fair though to give it a beating. I do want to make crystal clear though that the Brevitas is NOT rated for this flow factor, despite having endured this test and more with no apparent ill effects. So what did it sound like? Loud. Uncomfortably loud. Unpleasantly loud. Loud like you want to wear hearing protection loud. The only kind thing I can say about it, is that it is an improvement over the Dreamline’s bare muzzle, shrouded or unshrouded. It is loud, and it is fairly sustained. Don’t let the scale fool you, there is nothing quiet about this muzzle report. I do believe I’m correct in saying this is the loudest measurement of a moderator I’ve ever taken.