FX IMPACT M4 EXTENDED (FAC)

The M4 Impact is the latest premium airgun from FX and, although visually quite similar to the previous M3, it has a few key differences. The Extended rifle arrives in a deluxe hard case, and I was pleased to see that it fits inside without the need to remove the supplied moderator. There’s space for a generously sized scope, and there is a ½” thread at the muzzle of the compound barrel structure (which uses a liner within the barrel and outer 28mm diameter shroud). This is how FX is able to offer shooters multiple twist rates for their chosen projectile. The liner in the airgun on test is a Superior Heavy STX unit intended for weighty pellets and slugs. With a length of 800mm, the barrel offers enviable space for all that expanding air to drive the projectile. The entire barrel unit can be removed from the rifle and swapped over for different lengths and twist rates if desired. It also allows, in conjunction with changing the magazine and probe, the delivery of a variety of calibre options—.177, .22, .25, .30, and .35—to fulfil your desires for hunting or competition use on targets. Personally, I prefer FAC airguns of .22 or .25 calibre, as I feel these are most appropriate for UK shooters.

Bullpup
The Impact is a bullpup design, where the barrel extends from the muzzle almost all the way back to your shoulder, with just enough space for a butt pad and magazine. This is good, as a longer barrel gives more power and efficiency.
FX has now beefed up the aluminium receiver’s top strap, which has a flush 11mm dovetail to which the detachable Picatinny rail clamps in four places. This is advertised as enabling a greater range of scope movement to suit your optics’ eye relief. That said, it clamps securely and has little need to be adjusted. The Picatinny rail itself provides ample space.

Back to front
The black, hard-anodised receiver/stock features a cheekpiece that’s bolted in position. In use, it is comfortable and offers good scope alignment with medium-height rings above the Picatinny rail. At the very rear, the curved, hard polymer recoil pad offers 27mm of vertical adjustment via a locking screw on the right side.
Working forwards, the rotary magazine slots into the right side of the receiver when the cocking lever is pulled back. The mag is loaded by rotating the locking clasp, removing the clear cover, and then rotating the inner drum to compress the spring. This locks the first pellet in place and allows you to fill up the rest of the slots. Next, re-fit the clear cover, rotate the clasp, and insert the magazine back into the rifle.
Closing the cocking lever allows the probe to push a pellet through the mag and into the breech. Each time you cycle the action, the magazine rotor will progress one place and offer a new pellet. When you run out, the rotor will prevent the bolt from closing.

Reg and trigger
The regulator pressure gauge is positioned underneath the butt, and it’s an uprated Brass piston AMP unit capable of working up to 170bar. There is now a larger 75cc power plenum chamber ahead of this to further smooth out airflow.
The AR-15-type grip has been slightly enlarged and shows a rubberised, ambidextrous palm swell for tactile security when handling the gun. The new adjustable Quick Set Trigger tunes to single or two-stage settings with adjustable weight, plus the position of the 9mm wide blade can also be adjusted. The test rifle arrived with a two-stage setting, breaking at 620g (20oz), and the pull was crisp and predictable. Also, the trigger guard provides enough space for a gloved finger.
As supplied, the length of pull was 355mm (14”), with a 72mm reach from the throat of the vertical pistol grip to the blade.

Full of air
The cocking lever sits on the right-hand side, above the trigger, and it is very smooth and light to operate. It can be swapped to the left side of the rifle for left-handed shooters, although the magazine will only fit on the right side. The cocking handle is 14mm in diameter and 50mm tall, so it’s easy to grasp quickly. All trigger adjustments are accessible via a slot in the underside of the integral trigger guard, and the capped Foster filling connector is proud on the underside. These are reliable and don’t leak.
The carbon-fibre buddy bottle is removable, and this one is 580cc and can be filled to 250bar. There’s a pressure gauge on the right-hand side of the action and a 35mm long section of Picatinny rail in front of it for a compact bipod clamp. Twin side-mounted Picatinny rails enable accessory mounting, and the valve adjuster screw is nestled below these, just above the bottle. Both the Macro and Micro power adjusters are situated on the left side of the rifle.

Power vs precision
Given the Superior Heavy STX liner, I decided to try the gun with some 33.95gr JSB pellets. Scope mounting was simple, and head alignment from stock to ocular body was linear without any discomfort. The cheekpiece rollover pad is polymer, which prevents it from drawing heat from your face. In sub-zero conditions, along with the rubber grip, this made the gun very pleasant to use.
Loading the magazine is easier now because it features a stronger spring and five dimples in the rotor, which makes compressing that spring far easier. The magazine is now 14.7mm thick, with an internal capacity for projectiles measuring 12.1mm in length.
The initial power output from the box was 79 ft/lbs, with the pellet travelling at 1024fps. I shot two magazines (50 shots) through the gun to lead-line the barrel while I zeroed the rifle, then I did a 250bar refill before I started tuning. FX recommends that users keep the projectile speed between 850 and 950fps, and I have generally found this to be the case with rifles in the past.
During use, I adjusted the valve and observed both the muzzle report and projectile speed decrease as I shot subsequent groups. I topped up the buddy bottle every 50 shots. The adjuster valve is deeply nestled between the bottle and shroud, but it is smooth to rotate and has circumferential grooves to illustrate its position.
The groups shot at 50m tightened up significantly as I approached 900fps, and as I got to 860, the occasional flyers seemed to vanish. At this point, the FX was delivering 55 ft/lbs consistently, with five-round groups at 50m measuring below 16mm. The extreme spread was 9fps.

Minor details
Up until this point, I had left the 16-stage, left-side Macro adjuster on the maximum setting, and the Micro adjuster on four. This was to ensure that I was only altering one major variable (the valve) at a time. If I was keeping the gun long-term, I might test and tune multiple pellet types, but for the purposes of this review, I wanted to make sure the gun was delivering on target, rather than going on an endless tuning adventure. Once you have chosen your favourite projectile, the Macro Power adjuster allows immediate speed/energy control. I ran the gun as low as 7.4ft/lbs with a light pellet, but realistically, is anyone going to do this? Unlikely on such a large rifle.

Conclusion
The handling characteristics are undoubtedly better suited to benchrest shooting, tripod use, or the prone position rather than to a walking stalker. The rifle has no sling mounts, is long at 1120mm (44”), and weighs 3.4kg (7.4lbs) without the scope. The height of the rifle is also significant on a vertically stacked build like this.
Companies like Saber Tactical make additional Picatinny rail extensions for bipod mounting, and I would suggest this is a wise purchase, as although the carbon-fibre bottle can be a supporting member from a rest bag—or you can add a bottle clamp for bipod mounting—I’m always cautious of using high-pressure valve assemblies as stress-bearing members. I will also say the long, compound barrel structure is susceptible to slight zero shift if bumped during handling, but the rifle will certainly deliver the projectiles where you want them, as long as you want to keep up with the tuning and maintenance as part of your hobby, not just the shooting.