FX Impact M4 .35 Review: The Benchmark Hunting PCP Air Rifle

There is a specific problem the FX Impact M4 .35 was built to solve. A stubborn sounder of hogs digging up the back forty at 4 a.m. A raccoon pattern under the chicken coop. A neighbor's property line 90 yards away and a county noise ordinance you can't afford to break. A .308 solves the animal problem and creates three new ones — hearing damage, angry neighbors, and a phone call from the sheriff. A .22 rimfire is quieter but leaves you undergunned on anything larger than a groundhog. The Impact M4 in .35 caliber sits in the exact gap between those two, and it does it on stored air instead of powder.

This is not a plinking rifle and it is not a range toy. It is a high-end pre-charged pneumatic (PCP) hunting platform that throws an 81-grain slug at manufacturer-published 830 FPS for a manufacturer-published 124 FPE of muzzle energy — enough for humane, ethical harvest of pests, predators, and small-to-medium game inside 100 yards, with the acoustic signature of a suppressed rimfire. This review covers what the M4 actually is, what specs the manufacturer publishes, who should buy one, who shouldn't, and three cheaper regulated PCPs that solve part of the same problem for a lot less money.

Check today's price on the FX Impact M4 at Pyramyd Air →

The Spec Sheet (Manufacturer-Published)

Everything below is pulled from FX Airguns and Pyramyd Air's published product data for the FX Impact M4 in .35 caliber. No shooter-claimed numbers, no lab reports, no "muzzle velocity" borrowed from a different caliber. If a spec is not on this list, the manufacturer does not publish it and neither will we.

Spec	FX Impact M4 .35 Caliber
Powerplant	Pre-charged pneumatic (PCP), regulated
Max velocity	830 FPS (with 81gr pellet)
Max energy	124 FPE (with 81gr pellet)
Barrel length	23.62 in, rifled, shrouded
Overall length	34 in
Weight	6.85 lbs
Magazine	18-round rotary
Air cylinder	480cc carbon fiber
Fill pressure	3625 PSI / 250 BAR
Shots per fill	35
Action	Sidelever
Trigger	Two-stage adjustable
Safety	Manual
Stock	Synthetic

Two numbers are worth pulling out of that table. The 35 shots per fill means one 480cc bottle carries you through nearly two full magazines of full-power .35 slugs before you refill — enough for a night of pest control or a morning of squirrel hunting without hauling a compressor. The 250 BAR fill pressure is the working pressure, not the max; aftermarket carbon-fiber bottles let the M4 accept 300 BAR fills for even higher shot counts, though FX's own bottles are rated to 250.

What Actually Makes the M4 the Benchmark

Cheaper PCPs at $500 to $900 will happily throw a heavy pellet fast. The Impact M4 costs several times that because of what it lets you change. The M4 is a modular tuning platform, not a fixed-configuration rifle. Barrel liners swap through the Smooth Twist X barrel system, so a single lower can run .177 for backyard target work, .22 or .25 for small game, .30 for coyote, or .35 for the heaviest slugs the platform accepts. Hammer spring tension, valve dwell, regulator pressure, and the Power Plenum are all user-adjustable without a gunsmith — you tune the rifle to the specific slug you're feeding it until group size at 50 yards collapses onto itself.

The M4 revision (introduced 2023-2024, replacing the MkII) added a redesigned magazine built from stronger material with an improved rotation mechanism specifically to handle the weight of the heavier slugs the platform now shoots, and a brass piston regulator rated to 170 BAR working pressure. On paper those are small changes. In practice, the M4 is what fixed the reliability complaints .30 and .35 shooters had about the older MkII's magazine slipping under load.

Who the FX Impact M4 .35 Is For

Buy the M4 .35 if any of the following describe your actual use case:

• You have a persistent, close-range pest problem where discharging a firearm is legally, socially, or acoustically impossible. Suburban hog encroachment, rural properties with neighbors inside 300 yards, HOA-adjacent land, and pest problems near livestock all fall in this bucket.

• You are already deep into airgunning and want the ceiling of the hobby. If you've owned a Marauder, an Avenger, or a Gauntlet and you're now hitting the limits of what a fixed-tune rifle can do, the M4 is the natural upgrade path. You know what a regulator is, you own or can afford a hand pump or 4500 PSI tank, and "tuning to the pellet" is a phrase that means something to you.

• You want one rifle that covers a wide envelope instead of five. The interchangeable barrel liners genuinely let one Impact lower handle plinking, small game, medium game, and predator work by swapping the top end — something no fixed-caliber PCP can do.

• You are running large-game airgun trips where the .35 slug's energy is the point. Deer-legal air rifle states are a small list (Missouri, Virginia, and a handful of others, each with their own energy floors — verify your specific state's regulations directly with your fish and wildlife agency), but the M4 .35 puts you inside the published FPE thresholds many of those states set.

Who the FX Impact M4 .35 Is NOT For

Honesty check — if any of the following apply, you're better off with one of the alternatives in the next section.

• You want to plink cans in the backyard. A $400 break-barrel or a $700 regulated Avenger will make you just as happy on tin at 25 yards. The M4's tuning depth is wasted on plinking, and .35 slugs are expensive compared to .22 pellets by weight and volume.

• You've never owned a PCP before. This is not a first PCP. There are too many adjustable variables, and if you set the hammer spring or regulator wrong you'll spend a month wondering why groups are opening up. Buy a Marauder or an Avenger for a season, learn to fill and tune, then step up.

• You don't own or plan to buy a fill source. A 4500 PSI carbon-fiber tank or a good electric compressor is $400 to $1,500 on top of the rifle. Hand pumps to 3625 PSI exist but are punishing above 200 BAR. Budget the fill source before you buy the rifle, not after.

• You want an AR-15 replacement for home defense. A .35 slug at 830 FPS is a serious projectile, but a bolt-action side-lever PCP that requires a 30-second bottle refill after 35 shots is not a defensive firearm. Buy an actual firearm for that job.

• Your total budget is under $2,000 including scope and fill source. The rifle alone is at the top end of the PCP market. Add a scope worth mounting to it (Element, Athlon, or better in the 4-16x class), rings, an air source, and a tin of slugs, and you're inside the price of a used entry-level truck. If that math hurts, the alternatives below solve 60-70% of the problem for 25% of the money.

Three Regulated PCPs That Solve Part of the Same Problem

None of these three will out-shoot an Impact M4 .35 at 90 yards on a heavy slug. But each one is Amazon-verified, regulated, and honestly capable inside the envelope its price implies. If you're not ready to spend Impact money, one of these is where to start.

Air Venturi Avenger .25 — the value benchmark

Air Venturi Avenger, .25 Caliber Regulated PCP, Synthetic Stock · Regulator externally adjustable up to 3,000 PSI / 210 BAR · Max fill pressure 4,351 PSI / 300 BAR · 11mm dovetail + Weaver combo scope rail · Picatinny forend rail · Two-stage adjustable trigger · ~6 lb weight · Fully shrouded barrel

The Avenger is the rifle that changed the "you have to spend $1,500 to get a regulated PCP" conversation. Externally adjustable regulator — not internal, not fixed — means you turn a screw with the fill probe attached and read the reg pressure directly. Same tuning concept as the Impact at a fraction of the price. .25 caliber is the honest sweet spot for most airgun hunters: enough energy for squirrels, rabbits, raccoons, and coyote at reasonable range without the ammo cost or fill demand of a .35 platform. If you're going to own exactly one PCP, this is the one to argue for.

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Umarex Gauntlet 2 SL22 — the side-lever workhorse

Umarex Gauntlet 2 SL22 .22 Caliber PCP with Side Lever Cocking · Manufacturer-published up to 1,130 FPS in .22 · State-of-the-art pressure regulator · 10-round rotary magazine + single-shot tray · M-LOK accessory slots · Adjustable cheek piece · Quick-disconnect sling mount · Large knurled bolt handle

The Gauntlet 2 SL is the .22-caliber companion to what the Impact does at bigger bores. Side-lever action instead of bolt (faster follow-up, matches the M4's ergonomics), M-LOK forend for lights and bipods, and a regulator that keeps velocity honest shot-to-shot. Umarex's magazine indexing is the least fussy in this price class. If you want a regulated PCP that shoots like a modern rifle instead of a modern airgun, this is the one.

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Benjamin Marauder .22 (Wood Stock) — the American standard

Benjamin Marauder BP2264W .22-Caliber PCP, Wood Stock · Bolt-action multi-shot · Choked, shrouded barrel for consistency and quiet operation · 8-round auto-indexing magazine · Two-stage adjustable trigger · Reversible bolt handle · Ambidextrous hardwood stock · Made by Crosman in the USA

The Marauder is the rifle that made American PCP hunting mainstream. Not the cheapest, not the newest, but the one most experienced airgunners cut their teeth on and still recommend. The choked shrouded barrel makes it one of the quietest fixed-tune PCPs in this class, and Crosman's aftermarket support — parts, seals, hop-up kits, replacement bottles — is deeper than any imported brand. If you want a PCP with a 15-year proven history that you can still get service for in 2036, this is it.

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Pro Tips (Real, Not Filler)

• Tune to your slug before you buy a case. The M4's power adjustment window is wide enough that a 25-grain pellet and an 81-grain slug want completely different hammer spring tension. Buy one tin each of two or three candidate slugs (JSB, NSA, FX), chrono each at the same settings, adjust, chrono again. Only then buy in volume. This is the difference between one-ragged-hole groups and mystery flyers.

• Get a real air source before the rifle ships. The two workable answers are a 4500 PSI carbon-fiber tank ($400-$700 including yoke and fill station) or an electric compressor like the Air Venturi Nomad III or Yong Heng ($350-$1,200). Hand pumps work up to about 200 BAR before the shooter becomes the bottleneck; above that they punish you. Do not buy the rifle and then figure out fills.

• Mount a scope that respects the platform. A $150 optic is the wrong scope on a $2,000+ rifle. Aim for something in the 4-16x class with a real side-focus parallax and repeatable turrets — Element Titan or Helix, Athlon Argos BTR, or Vortex Diamondback Tactical are the honest starting points. FFP if you plan to hold over for wind at extended range.

• Log your fill curve. The M4 is regulated, which means it will hold consistent velocity across most of the bottle — but there's a "shot count cliff" where the reservoir drops below regulator set pressure and velocity falls off. Chrono the last 10 shots of a fill on your specific tune. Once you know shot 32 is where velocity starts to drop, you stop hunting at shot 30 and refill.

• Store it de-pressurized only if you're storing it long-term. Short-term (weeks to a few months), leave the bottle at working pressure — seals stay seated. Long-term storage (6+ months in a safe you won't touch), degassing prevents seal set. This is a maintenance nuance most first-time PCP owners get wrong in one direction or the other.

FAQ

Is the FX Impact M4 .35 legal to hunt with in my state?

State-dependent. Air rifle hunting regulations vary widely and change year to year. States like Missouri, Virginia, Arizona, and Michigan explicitly allow air rifles for certain game with minimum caliber and energy floors that the M4 .35 clears; others prohibit air rifles for game entirely; a handful allow small game only. Do not rely on a review for legal advice — check your specific state's fish and wildlife agency regulations for the current year before you hunt.

How loud is it, really?

Roughly comparable to a suppressed .22 rimfire when the shrouded barrel is dry and clean, per shooter reports at reviewed velocity ranges. The action cycling and the slug's downrange impact often make more noise than the muzzle. This is not "silent," but it is quiet enough that neighbors 100 yards away won't identify it as gunfire.

Can I use the same rifle for .22 pellets and .35 slugs by swapping barrels?

Yes — that's the entire point of the Smooth Twist X barrel liner system. FX sells caliber conversion kits that swap the barrel liner, magazine, and probe. You keep the same lower, regulator, and bottle. Budget $400-$700 per additional caliber conversion depending on twist rate and length.

Do I need a special license to buy or own it?

Federally, no — air rifles are not firearms under U.S. federal law. Some states and cities (New Jersey, parts of Illinois, New York City) regulate air rifles like firearms with age minimums, permits, or transport rules. Verify your local law before ordering.

How many shots before I need to refill?

Manufacturer-published 35 shots per 250 BAR fill at full .35 tune. Turn power down or shoot lighter slugs and shot count climbs; turn up and it drops. A carbon-fiber tank fills the M4's 480cc bottle in under a minute, so refill logistics are not the issue for a day at the range — the issue is remembering to top off before you leave the truck for a stalk.

The Bottom Line

The FX Impact M4 .35 is what you buy when you already know what you need it for. It is the benchmark platform in high-end airgun hunting because it is the most tunable, most modular, most caliber-flexible PCP the market currently sells — and because 124 FPE at the muzzle on a heavy slug puts it inside the energy envelope for humane, ethical harvest of medium game and any pest problem you can encounter in a suburban or rural environment.

It is also expensive, requires a real fill source, and rewards experience the way a race car rewards a driver who already knows how to drive. If that describes you, no other rifle in this class does what the M4 does. If it doesn't, the Air Venturi Avenger .25 solves 70% of the same problem for less than a third of the money and is the honest first PCP for the buyer who wants to grow into the hobby before spending Impact money.

Check today's price on the FX Impact M4 at Pyramyd Air →