Air
Home to the world's quietest airgun moderators, plus precision pellet caddies, self-healing targets, chassis parts, and shooting accessories, all designed and manufactured by Silent Thunder Ordnance. From the Accipiter and Sarissa lines to the Pocket Benchrest and Eyeshine Targets, this is the full catalog of STO air products built for performance and tested before they ship.
Falx
Falx
The Falx is our mid-size standard moderator, carrying a dimensional envelope of 40x170mm and a weight of approximately 193 grams. It covers the full range of standard through high flow applications in a more compact package than the Sarissa, and for most rifles it is the natural starting point.
The design uses Nikola Tesla's Gas Diode to reflex propellant air back on itself, resisting forward flow through geometry alone with no moving parts. This three-stage approach first strips air off the pellet to reduce turbulence and improve accuracy, then delays it through compound gas diode stages, and finally passes it through a high-performance damping section to absorb residual sound energy. Critically, the design adapts along its length rather than repeating a single approach end to end, applying the right technique at the right point in the air's journey through the moderator.
The anodized aluminum tube is serviceable and modular. Cores can be swapped as the technology advances, meaning a Falx purchased today can be upgraded rather than replaced as new revisions become available.
Key Features:
Tesla Gas Diode design: Compound diode stages reflex and delay propellant air through geometry alone, no moving parts
Adaptive staged architecture: Design transitions along its length to maximize attenuation at each point in the air's travel
Tapered bore: Improves sound attenuation while reducing the likelihood of pellet clipping
Modular serviceable construction: Anodized aluminum tube allows core replacement as technology advances
Flow factor variants: Standard, Moderate, and High flow cores available to match your rifle's specific output
Big bore cores available: Expanded bore options accommodate larger caliber rifles up to High flow; space constraints preclude an Extra High flow variant at this size
Built and tested in the USA
Select the core whose flow factor most closely matches your rifle's calculated value. Information on calculating your rifle's flow factor can be found in our Moderator Configuration & Optimization guide.
This product is intended for airgun use only. Use of this product in any manner inconsistent with its design intent is a violation of federal law. More information about the federal court ruling which clarified the legality of airgun moderators in the United States can be found here. Local restrictions may still apply. It is the responsibility of the buyer to ensure compliance with all applicable laws.
This item ships within the United States only.
Selecting the Right Variant
Matching your moderator to your rifle's flow factor is the single most important step in getting the best performance out of a Falx. Our Moderator Configuration & Optimization guide walks through how to calculate your flow factor and what to do with that number. The three Falx variants are tuned to the following reference hosts:
Standard Flow: Tuned on an FX Crown .22, 32 ft-lbs. Factory config w/ extended shroud, acoustic peak 288.0. Flow factor 460.
Moderate Flow: Tuned on an FX Crown .30, 80 ft-lbs. Factory config w/ extended shroud, acoustic peak 637.6. Flow factor 1,111.
High Flow: Tuned on an FX Dreamline .30, 87 ft-lbs. Bare muzzle, acoustic peak 3,668.4. Flow factor 6,500.
Extra High Flow: Tuned on an AEA Challenger .35, 150 ft-lbs. Bare muzzle, acoustic peak 5,255. Flow factor 16,333.
If your rifle falls significantly outside this range, or requires an Extra High flow variant, consider the Sarissa which accommodates the full four-variant range in a larger envelope. If your rifle falls significantly outside these ranges entirely, get in touch before ordering.
Sound Profile Data
A note on reading these traces: peak alone doesn't tell the full story. Post-peak sound character has a substantial effect on perceived loudness, often more than the peak value itself. Each trace is provided so you can evaluate the full sound profile rather than a single number. Note that traces are not shown to the same scale.
Falx Standard Flow Rev.3, as tested on a shrouded FX Crown .22. Average peak 44.21.
Rev.3 represents a complete re-engineering of our damping system, combining the diode advances of previous versions into a more integrated structure while dramatically increasing closed damping material surface area and more precisely tuning open damping material flow resistivity and impedance. At standard flow the Falx delivers a very quiet result, with both peak and post-peak sound well controlled.
Falx Moderate Flow Rev.3, as tested on a shrouded FX Crown .30. Average peak 69.12.
At moderate flow the rev.2 diode geometry comes into its own. Hollow expanded struts serve double duty as structural members and flow channels feeding the diodes directly, freeing up internal volume and increasing stopping power over the rev.1 design. Both peak and post-peak sound are well managed at this flow level.
Falx High Flow Rev.3, as tested on an unshrouded AEA Challenger Pro LB .35. Average peak 857.41.
At high flow conditions the Falx is running into the limits of its size, and that shows primarily in post-peak sound. There simply isn't space for the additional damping and diode stages that would clean it up further; that's what the Sarissa or Mus is for. What the Falx does do at this power level is bring the sound signature down to something comfortable and manageable, adding only modestly to the rifle's overall length in the process. For this same reason there is no Extra High Flow Falx variant; at that power level the size constraints become a hard ceiling on performance.
