A Conversation at the IWA 2026 Conference
Every once in a while you come across a product that quietly fixes several problems at the same time. That was my takeaway after spending time with the FX team at IWA this year. While walking the show floor and catching up with Johan from FX Sweden, we started talking about the company’s newest barrel systems that were being introduced at the show.
At first glance they look like a natural evolution of the FX platform, but the more time you spend understanding what they changed and why they changed it, the more you realize these barrels address several things shooters have been wrestling with for years. The improvements show up in consistent precision, harmonic stability, and something that matters a lot to anyone running a DonnyFL moderator on their airgun: bore alignment. And when bore alignment improves, something else improves with it—quieting your shot report.
The Hidden Challenge in Typical Airgun Barrel Systems
To understand why these new FX Airguns solid barrel housings matter, it helps to step back and look at how most modern airguns have traditionally been built. For many years the airgun industry has relied heavily on shrouded barrel systems. In this design, a relatively thin barrel liner sits inside a larger outer shroud that helps manage the expanding air that follows the projectile out of the muzzle.
It’s a design that works well for reducing noise and stripping air, but it also introduces multiple parts and connection points. The liner may sit inside a barrel housing. That housing may interface with an air stripper or internal shroud structure. The outer shroud then typically carries the threads that allow a moderator to be attached to the front of the airgun. Each one of those interfaces introduces another opportunity for fault tolerance to stack.
Most of the time those tolerances are small enough that the airgunner never notices them. But if several small variations line up in the wrong direction, the bore of the barrel and the bore of the DonnyFL moderator can end up slightly out of alignment. When that happens the first thing shooters often see is accuracy starting to fall apart. A projectile barely touching an internal surface inside a moderator can turn tight groups into flyers. In more severe situations a solid strike inside the moderator can damage the internal structure entirely.
Because of that risk, many airgunners and our tech support here at DonnyFL developed a simple workaround over the years. Instead of running a moderator that exactly matches their caliber, they move up one size. Someone shooting a .22 airgun might run a .25-rated moderator, and a .25 shooter might jump up to a .30 moderator. The larger opening inside the moderator creates additional clearance and reduces the chance of clipping if alignment isn’t perfect. It works well enough, but it also gives up some shot report reduction performance in the process.
The Science of Bore Clearance and Sound Suppression
Across the broader world of shooting sports where shot suppression has been studied for decades, one principle shows up again and again. The closer the internal bore of the suppressor is to the diameter of the projectile, the more efficiently the device can control the expanding air column behind that projectile, leading to a quieter shot report.
Airguns operate differently from firearms in several important ways. We are dealing with compressed air rather than burning powder, and we do not have to deal with the extreme heating and cooling cycles that firearm suppressors experience. But the airflow physics still follow many of the same rules. When a projectile exits the barrel, it is followed by a column of compressed air, and that rapidly expanding air is what produces the sharp report we hear. A moderator works by slowing and redirecting that expanding air through internal chambers before it reaches the open atmosphere.
The amount of clearance between the projectile and the internal bore of the DonnyFL moderator determines how much of that air can escape straight forward, increasing the uncorking effect. Otherwise known as a louder shot report.
To illustrate that relationship, consider a typical .22 caliber airgun slug that measures about 0.218 inches in diameter. Many moderators designed specifically for .22 airguns will have an internal bore opening around 0.250 inches. That leaves about 0.032 inches of total clearance around the projectile, or roughly 0.016 inches on each side. In that configuration the projectile fills a large portion of the passage through the moderator. As the slug travels through the bore, much of the expanding air is forced outward into the moderator’s internal chambers where it can be slowed and redirected. This allows the moderator to manage the airflow more efficiently and ultimately produce a quieter shot.
Now compare that to the workaround many airgunners use when they are concerned about alignment. Instead of running the .22 moderator with the 0.250-inch bore, they step up to a .25-rated moderator that has a bore closer to 0.300 inches. The same 0.218-inch projectile now travels through a bore that has roughly 0.082 inches of total clearance, or about 0.041 inches on each side.
That larger opening dramatically reduces the risk of clipping if the system is slightly out of alignment, but it also allows a much larger portion of the expanding air to escape forward around the projectile rather than being redirected inside the moderator’s chambers. The moderator still reduces the shot report, but it cannot manage the air quite as efficiently.
The quietest airgun system possible is one where the bore clearance remains tight while the moderator stays perfectly aligned with the barrel. Historically, achieving that balance has been difficult with multi-piece shrouded barrel systems.
The STX Liner System That Changed the Sport
Before looking at the new barrels themselves, it is important to understand the system they are built around. The FX STX liner system has been one of the most important innovations in modern airgunning. When FX introduced interchangeable liners with different twist rates and choke profiles, it fundamentally changed how shooters approached tuning their airguns.
Instead of being locked into a single fixed barrel design, shooters could swap liners and tailor their airgun to different projectiles. Pellets, slugs, heavier ammunition, and different velocities all became part of the tuning process. With a simple liner swap, the same airgun could be optimized for a completely different shooting application.
In many ways the STX system became one of the shining stars of the sport. At the same time, it has also been one of the more misunderstood systems.
As shooters began pushing these airguns harder, new variables entered the picture. Slug shooting became more common. Power levels increased. Regulators were pushed higher and airguns started producing more aggressive shot cycles. In most cases the STX system handled these changes very well, but occasionally shooters would encounter harmonic tuning challenges or small point-of-impact shifts that were difficult to diagnose. Not every airgun showed it, but when you look at the mechanical layout of the system it makes sense. The STX platform uses a removable liner that sits inside a barrel housing. That modular design is exactly what gives the system its flexibility, but it also means the liner is not a single continuous piece of steel like a traditional solid barrel.
The Evolution: FX’s New Barrel Housings
As the sport evolved, it appears FX engineers began looking for ways to strengthen the relationship between the liner and the barrel housing. The new 14mm barrel system and the Bull Barrel system are a direct response to that evolution.
Both barrel housings are machined to much tighter tolerances around the STX liner so that once installed, the liner is supported more securely inside the housing. The goal is to create a structure that behaves as close as possible to a solid barrel while still preserving the advantages of the interchangeable liner system.
Shooters still get the ability to swap liners, experiment with twist rates, and tune choke profiles for different projectiles. But the barrel housing now provides greater rigidity and improved harmonic stability. With less movement between the liner and the housing, the barrel system behaves more predictably during the firing cycle and can handle the energy of modern high-power airgun setups more consistently.
Why This Matters for DonnyFL Moderator Alignment
There is another benefit that comes along with that tighter relationship between the liner and the barrel housing, and it ties directly back to moderators.
When the liner is secured more precisely inside the housing, the entire barrel assembly maintains better bore concentricity from breech to muzzle. The more precisely that liner sits inside the barrel assembly, the more predictable the alignment becomes between the bore and the threaded muzzle where the DonnyFL moderator mounts.
The FX Bull Barrel takes this concept a step further by providing direct threading on the barrel itself. Instead of attaching a moderator to an outer shroud that may or may not be perfectly centered around the liner, the moderator now references the barrel directly. That removes several alignment variables and greatly improves the chances that the bore of the moderator will remain perfectly concentric with the bore of the barrel.
A Better Opportunity for Maximum Sound Reduction
For shooters running DonnyFL moderators, this improvement creates a real advantage. With the barrel liner now secured more precisely inside the housing and the muzzle threads referencing the barrel directly, shooters have a much better opportunity to run a moderator that is closer to their actual projectile diameter.
Instead of stepping up to a larger bore moderator purely as insurance against alignment issues, they can confidently run a caliber-matched DonnyFL moderator with tighter internal clearance. That tighter clearance forces more of the expanding air into the moderator’s internal chambers where it can be slowed and redirected, ultimately resulting in better sound suppression.
Accuracy, Suppression, and the Best of Both Worlds
Standing there talking with Johan at IWA, it was clear these new barrel systems were not designed to chase a marketing headline. They were designed to solve real-world issues shooters had started encountering as the sport evolved and airguns were pushed to higher levels of performance.
I can attest to this as I have been running a prototype of the solid 14mm barrel system in my FX King with Saber Tactical Chassis system for the past year and can speak from first hand experience with this barrel system. Hands down this approach strengthens the relationship between the liner and the housing. The Bull Barrel adds even more rigidity and provides a direct-threaded muzzle for improved alignment, which I will be testing next. Together these new systems maintain the modular flexibility that made the STX liner system famous while addressing the harmonic and alignment challenges that sometimes appeared when shooters began pushing these platforms harder.
For shooters pairing their airguns with a DonnyFL moderator, the benefits become immediately clear. Improved bore alignment allows tighter moderator tolerances, which improves sound suppression while reducing the risk of clipping. Combine that with greater harmonic stability and the continued flexibility of the STX liner system, and the result is a setup that performs better across the board.
From where I stood at IWA talking with the FX team, the outcome felt pretty clear. Accuracy improves. Sound suppression improves. And shooters get to keep the modular flexibility that made the STX system such a breakthrough in the first place.
That’s a win on both sides of the equation.
