Setup · FX Impact M4

My FX Impact M4 slug setup for hunting

By James · Updated September 24, 2026 · Editorial policy

My exact setup: an FX Impact M4 in .22, tuned by Utah Airguns for heavy slugs: heavy slug liner, slug power kit, high-flow transfer ports, tungsten hammer weight, regulator at 150–170 bar, and a slug probe. It shoots 40.1gr ACE FRAG slugs at about 950 fps (~80 FPE) under a DNT Zulus 4K scope cam. It's built for 100+ yard shots on small game, which is more rifle than most hunters need.

How this was tested

Field protocol: every load gets a 10-shot chronograph string (average velocity, extreme spread, energy) before it's trusted on game. Holdovers are confirmed at real distances, then re-confirmed in field conditions. Shots are recorded through the scope cam, and claims on this page link to footage where it exists. Full methodology & editorial policy →

The setup on this page, hunting through the Zulus 4K.

The build, part by part

Component	What's on mine	Why it matters for slugs
Rifle	FX Impact M4, .22	Regulated, modular bullpup with power adjustment and caliber/liner swaps
Tune	Done by Utah Airguns	Heavy slugs need the whole system matched: liner, air flow, and hammer
Barrel liner	Heavy slug liner	Stabilizes long, heavy slugs that a pellet liner may not
Power	Slug power kit + high-flow transfer ports	Moves enough air to push 40gr slugs at useful speed
Hammer	Tungsten hammer weight	More hammer mass for the heavier load
Regulator	150–170 bar	Sets the pressure behind every shot; mine is tuned to this load
Probe	Slug probe	A standard pellet probe choked air flow with this setup
Projectile	40.1gr ACE FRAG slug	High ballistic coefficient; designed to fragment on impact
Velocity / energy	~950 fps / ~80 FPE	FPE = 40.1 × 950² ÷ 450,436 ≈ 80.3
Optic	DNT Zulus 4K (3–24x, records the shot)	Rangefinder + recording; full review

What it does in the field

Inside ~100 yards it's boringly reliable. That's this rifle's sweet zone on collared doves and rabbits.
Past 100 it gets humbling. On a good day in the desert, I was hitting tennis-ball-sized targets at 140–150 yards in 8–10 mph wind. On a collared dove hunt, 10 of my 15 shots missed, mostly at the long end. Both are true.
Zero drifts. I've had days where it shot perfectly, then needed a re-zero the next outing. Now I confirm zero before every hunt.
Rangefinders can lie. One day my readings were hit or miss. Cross-check with a second rangefinder when a shot is long.

Short: a 130-yard accuracy clip from the channel.

Should you copy this setup?

Copy it if

You regularly shoot past 60–70 yards
You hunt in wind
You'll tune and verify over a chronograph
You have ground with safe backstops for slugs

Don't if

Your shots are inside 50 yards (pellets do the job)
You hunt near houses, where over-penetration matters
It's your first PCP (start here)
You'd rather hunt than tinker

Three tuning rules I'd give anyone

Chronograph everything. A tune is just a guess until a 10-shot string shows the average and extreme spread.
Mind regulator creep. Regulators can drift up in pressure while a rifle sits. American Airgunner suggests setting the final regulator pressure 2–3 bar lower if first-shot consistency matters to you.
Change one thing at a time. Liner, hammer, regulator, and power all interact. Change two and you won't know which one helped.

Why energy isn't the goal here: my 80 FPE is about six times the floor for rabbits (FPE chart). The point of this build is a flatter, wind-resistant path at range, not a harder hit.

FAQ

What slugs does James Southern Outdoors use in the FX Impact M4?

40.1-grain ACE FRAG slugs in .22, shot from an Impact M4 tuned for heavy slugs at roughly 950 fps. That works out to about 80 foot-pounds at the muzzle.

Can a stock FX Impact M4 shoot 40-grain .22 slugs?

Heavy slugs like 40.1gr need more power and a barrel/liner that stabilizes them. My rifle was tuned for it: a heavy slug liner, a slug power kit, high-flow transfer ports, a tungsten hammer weight, and a slug probe. A stock rifle set up for pellets usually needs changes before heavy slugs group well.

What regulator pressure does your FX Impact M4 run for slugs?

My regulator is set in the 150–170 bar range. That's specific to my build and load. Tune yours over a chronograph, and don't copy numbers blindly.

How much FPE does a .22 FX Impact M4 make with slugs?

Mine makes about 80 FPE with 40.1gr slugs at roughly 950 fps. FX lists up to 87 FPE for the .22. That's far more than small game needs, and the extra energy is for range and wind, not deader rabbits.

Are slugs better than pellets for hunting?

Past about 50 yards, usually yes, because their higher ballistic coefficient holds speed and fights wind. Inside 50 yards, a pellet your barrel groups well is just as effective, cheaper, and safer near houses.

Sources

Written by James · Southern California airgun hunter. Every recommendation on this site comes from animals actually taken in the field with my own gear — an FX Impact M4 running 40.1gr ACE FRAG slugs under a DNT Zulus 4K, with every hunt filmed through the scope. If I haven't hunted with it, I say so. How gear gets tested here →

Keep reading

Rifle Review

Is the FX Impact M4 Worth It for Hunting?

Months of hunts, independent accuracy data, the full system cost, and who shouldn't buy one.

Read the review →

Field Guide

How Far Can You Hunt With an Air Rifle?

What 100+ yard airgun shots really take, with my own hit-and-miss numbers.

See the numbers →

Caliber Guide

Best Airgun Caliber for Small Game: .22 vs .25

The energy math, the trajectory truth, and slugs vs pellets from someone who shoots both.

Read the guide →