The Pinnacle of PCP

By Rob Mori (aka @hunt.aus) 

The FX Impact M4 stands as one of the most advanced and versatile pre-charged pneumatic (PCP) air rifles available today, continuing the legendary Impact series’ legacy while introducing meaningful refinements that elevate performance, usability, and precision. As an end-user who owns and has spent considerable time with this rifle in various configurations, from target shooting to field applications such as pest control, it’s clear why the M4 is frequently hailed as a benchmark in the high-end airgun market. 

Manufactured by Swedish innovator FX Airguns, the Impact M4 builds on the platform’s reputation for modularity and tunability. Released as an evolution of previous models, it retains the iconic bullpup design and cutting-edge aesthetic but manages to incorporate upgrades that address user feedback to allow boundaries to be pushed even further. Available in multiple configurations (Compact, Standard, Sniper and Extended) with barrel lengths ranging from 500mm to 800mm and calibres including .177 (4.5mm), .22 (5.5mm), .25 (6.35mm), .30 (7.62mm) and even .35 (9mm), the M4 offers something for virtually every shooter preference. 

One of the rifle’s standout features is its Smooth Twist X Superior (STX) barrel system. This interchangeable barrel and liner design allows users to swap calibres and even liner types (including specialised ones for slugs) with relative ease. The barrel can be removed and changed on the fly, making it incredibly adaptable whether you’re switching from lightweight .177 pellets for plinking all the way to heavy .30 or .35 slugs for long-range hunting. The rifling uses FX’s patented Smooth Twist technology, which delivers exceptional accuracy by minimising pellet deformation while optimising velocity and consistency. In practice, this translates to sub-MOA groups at 50-75m with properly tuned setups, even when pushing heavier projectiles. 

Power delivery is precisely managed through a suite of external adjustments that set the M4 apart from nearly every other competitor on the market. The Adjustable Match Precision MKII (AMP) regulator, which is now a single robust brass piston design, provides faster refresh rates, greater consistency and the ability to handle higher fill pressures (up to 250 bar max with regulator working pressures often around 170 bar). The external valve control lets you fine-tune air release for different ammo types or power levels without the need for disassembly. Complementing this further are macro and micro hammer spring tension adjustments, allowing precise control over dwell time and hammer strike. The Power Plenum 750 (with increased post-regulator volume) enhances efficiency and shot count, delivering impressive strings of up to 375 shots in .177, 330 in .22, and solid numbers even in larger calibres like .25 (160) or .30 (105) per fill, depending on your specific tuning setup. 

Its Quick Set Trigger system is another major highlight in the M4. Fully adjustable with a crisp, clean break and minimal creep, it offers a much finer feel than previous generations. I personally, and others who have used this model, describe it as “silky smooth” and competition grade right out of the box. Combined with the reversible sidelever (ambidextrous friendly for left- or right-handed shooters), cocking is effortless and fast, even during rapid strings. The new high-capacity magazines feature stronger materials and an improved internal mechanism for reliable feeding, even with heavy slugs (no more jams from overloaded drums). 

Ergonomics have also been refined, with the FX UG1 pistol grip (AR15-style mount) and vertically adjustable recoil pad improving cheek weld and overall comfort during extended sessions. The dual-rail optics mounting system (Picatinny on a 9-11mm dovetail with adjustable/removable 30 MOA rail) ensures rock-solid scope alignment with minimal POI shift, which became a common complaint addressed in earlier Impact models. The rifle’s overall build quality is superb: lightweight yet robust with premium finishes available in black or striking copper accents. 

What truly sets the FX Impact M4 apart from other air rifles is its unparalleled level of customisation and tunability without tools. Most PCPs offer some adjustability, but the M4’s external Quick Tune System lets you dial in power, regulator pressure, hammer tension and valve settings in the field or bench in minutes. This makes it ideal for experimenting with pellets vs. slugs, sub-12 ft-lbs FAC limits, or high-power setups (FAC versions excel here, pushing serious energy for hunting). Very few, if any, air rifles match its shot-to-shot consistency when properly tuned and when you factor in the zero recoil nature (typical of regulated PCPs), it truly allows for follow-up shots with pinpoint precision. 

In real-world use, the M4 shines across all disciplines. For target shooting and benchrest its accuracy is phenomenal, with five-cent piece-sized groups at 50-75 meters not being at all uncommon in .25 with sorted pellets or tuned slugs. Hunters appreciate the quiet report (around 86-90dB, with further reductions available via its suppressor-ready setup with muzzle threading), flat trajectory and devastating terminal performance on small to medium game. The lack of recoil makes it forgiving for extended hunts and the modularity means one rifle can handle everything from pest control to long-range varminting. 

The M4 also highly rewards ‘tinkerers’ and is not always a case of ‘set and forget’ for absolute beginners. Optimal performance often requires dialling in settings for specific ammunition or the task at hand. The M4 does find itself at a premium price point ($3,600+ depending on your preferred configuration and your selected retailer), which makes it an investment best suited for dedicated enthusiasts/hunters who value precision engineering and consistent accuracy over simplicity. 

Ultimately, the FX Impact M4 isn’t just an air rifle; it’s a precision platform that redefines what’s possible in the PCP world. Its combination of Swedish craftsmanship, endless adjustability, exceptional accuracy and forward-thinking features makes it stand head and shoulders above the competition. If you’re serious about air gunning and want a rifle that grows with your skills, the M4 delivers an experience that’s hard to match. I highly recommended it for anyone seeking the pinnacle of modern airgun technology.