FX Recommended Setup for the FX Impact M4 - 0.25 caliber

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jhinkens

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Oct 24, 2024
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I'm brand new to the airgun world and still working my way through the enormous amount of information available. So go easy on me. We all have to start somewhere.

OBJECTIVE:
Pest control at 75+ yards

EQUIPMENT:
FX Impact M4 Standard 600mm
FX STX Slug Liner 1:16 twist
Impulse Air IA-1200 Moderator
Element Titan 5-25×56 FFP Scope
Garmin Xero C1 Pro Chronograph
BOG Tripod

AMMUNITION:
FX Hybrid Slugs | .25 Caliber (26gr)

SETTINGS:
Regulator: 120
Valve: 4
Macro Wheel: 16
Micro Adjustment: 3.5
FPS: 950

QUESTIONS & CONCERNS:
Target Velocity - The good folks at Utah Air Guns recommended 950fps. I made the mistake of adjusting things without knowing what I was doing. Eventually, I got it consistently clocking 950 fps. My challenge is getting the grouping more consistent. I fill the tank to 250 bar, and refill it when it drops below 200. But even though the pressure drop in the tank doesn't seem to affect the FPS too much, it does seem to have an effect on the consistentcy and accuracy. More specifically, at 50 yards, it can be up to 1-1/2" to 2" groupings. So my question is what is the recommended velocity for the FX Hybrid Slugs in 26 grain? I tried dropping the velocity to 945 FPS using the micro adjuster but the grouping remained the same. I haven't tried increasing the FPS yet until I get some feedback from experienced users.

Also, what is the acceptable amount of variance in the FPS after everything is set? Presently, it seems to vary between 4 or 5 FPS at times. Maybe that's normal?

MODERATOR
I saw a tuning video where the gentleman posting tried several different moderators while tuning an M3 and ultimately removed them explaining that the moderators were causing some erratic groupings. I removed my moderator and replaced it with the factory muzzle. I didn't notice any difference and I also couldn't deterimine if the gun was any louder. Stock, it's pretty darn quiet. What do you experts out there feel about moderators?

SLUG LINER
After perusing this forum, I have seen a lot of controversy over the correct liner for 0.25 slugs. The one that was recommended by the folks at Utah Air was the 1:16 FX STX slug liner which I have installed now. I've read several threads that claim the FX STX 'Superior' Liner is the one to have. Which is best?

AMMUNITION
FX Hybrid Slugs | .25 Caliber (26gr)
There's a lot of differing opinions on the best slug to run. If there is something more preferable than what I'm shooting now, I'd sure like to hear about it.

Ending on a positive note, I have been thoroughly pleased with this new rifle. The ability to shoot with so little noise is really something. Super fun!

Thanks in advance for any recommendations offerred.
 
Maybe your gun doesn’t like the hybrids. My M4 doesn’t like them, neither the regular liner nor the slug liner. I get got groups at 50y with NSA 29gr and 34.9gr and H&N HP II. Still have to try ZAN. Finding the right slug your gun likes is an undertaking and you will have to try many different ones and different speeds.

Separately, did you clean your barrel? If not this light help as well!
 
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When I get a factory new gun the first thing I do is clean the barrel then put 1000 pellets through it. Even if it is going to be a slug gun. All I am doing is letting things settle and wear in.
You may have too much air going down the barrel. Try backing the micro adjuster down two clicks and shoot 10-15 shots noting the velocity of the last 3. Adjust down until you see a slight drop in velocity. Then do the same with the Valve knob. Adjust the valve knob in 1/4 turn increments until you see another small drop in velocity.
Once that is done you will know you have no excess air following your projectile out the barrel.
Be aware that shooting an air gun consistently is more difficult than a powder burner. The increased time the projectile spends going down the barrel makes good technique a must for consistent accuracy.
 
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I spent a great deal of time with .25 Hybrids out of a 600mm Impact for my dad. Shot more than 1,000 of them. Not because I think they are a good slug, but because they were a safer slug for his needs. They worked best for me out of the standard liner at 935fps. Unfortunately with an Impact there are 20 ways to arrive at 935fps, so I had to test them all to find the one that most consistent.

If you get tired of shooting giant groups at 50 yards, slide a superior standard liner in the gun and shoot some 33.95gr pellets out to 100 yards. Then at least you’ll be able to enjoy what the gun is capable of without having to kiss its a$$ too much. But you still have to know what you’re doing to get the most out of even pellets out of a FX.
 
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greenbeans said:
Maybe your gun doesn’t like the hybrids. My M4 doesn’t like them, neither the regular liner nor the slug liner. I get got groups at 50y with NSA 29gr and 34.9gr and H&N HP II. Still have to try ZAN. Finding the right slug your gun likes is an undertaking and you will have to try many different ones and different speeds.

Separately, did you clean your barrel? If not this light help as well!
Click to expand...
I cleaned the barrel when I first got it after putting about 30 rounds through it. Now I've got about 400 rounds through it so I'll clean it again to be sure. And I think I'll try those NSA slugs. I hear others saying how much they like them. Thanks!
 
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Chukar60 said:
When I get a factory new gun the first thing I do is clean the barrel then put 1000 pellets through it. Even if it is going to be a slug gun. All I am doing is letting things settle and wear in.
You may have too much air going down the barrel. Try backing the micro adjuster down two clicks and shoot 10-15 shots noting the velocity of the last 3. Adjust down until you see a slight drop in velocity. Then do the same with the Valve knob. Adjust the valve knob in 1/4 turn increments until you see another small drop in velocity.
Once that is done you will know you have no excess air following your projectile out the barrel.
Be aware that shooting an air gun consistently is more difficult than a powder burner. The increased time the projectile spends going down the barrel makes good technique a must for consistent accuracy.
Click to expand...
I'll give those adjustment tips a shot. Seems pretty straight forward. And I think you're right on technique. Prior to getting the FX Impact M4 I was shooting a HMR Hornady .17 caliber rimfire that I find easier to shoot, but perhaps I just need to practice more with the M4. This is all new to me I've never been that great of a shot anyway! ;-)
 
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Vetmx said:
I spent a great deal of time with .25 Hybrids out of a 600mm Impact for my dad. Shot more than 1,000 of them. Not because I think they are a good slug, but because they were a safer slug for his needs. They worked best for me out of the standard liner at 935fps. Unfortunately with an Impact there are 20 ways to arrive at 935fps, so I had to test them all to find the one that most consistent.

If you get tired of shooting giant groups at 50 yards, slide a superior standard liner in the gun and shoot some 33.95gr pellets out to 100 yards. Then at least you’ll be able to enjoy what the gun is capable of without having to kiss its a$$ too much. But you still have to know what you’re doing to get the most out of even pellets out of a FX.
Click to expand...
Thanks for the input. I ordered some NSA slugs today in both 29 grain and the 34.9. I'll give those a try and then see if the 935fps that worked for you will get me a little closer. Thanks.
 
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MongooseV8 said:
I would try installing the Standard liner and see how it compares with the FX Hybrids. The heavy liner doesnt like lighter slugs or pellets in my experience. Dont worry too much about the fps with slugs, concentrate on a nice balanced tune and accuracy.

2moa is typical with slugs, few people reach that magical <1moa.
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I spoke with a friend of mine today who said the same thing about the FX Hybrids and a slug liner not working well together. I'm going to try some NSA slugs first and if that doesn't show any improvement, I'll try swapping out the liner for the standard liner. I watched a couple YouTube videos and the liner swap out doesn't seem like to big of a deal. Any precautions I should take to avoid screwing anything up? Thanks.
 
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MongooseV8 said:
Dont over tighten the barrel jam nut and make sure you get all the liner orings out of the housing. Once you take it apart a couple times its a piece of cake.

My Heavy 25Cal liner really likes Nielsen 34.9g and 36.2g, but would likely do well with anything at least that heavy.
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I was just looking up that Heavy 25 caliber liner on Utah Airguns and they don't list one for the 600mm barrel. Not sure if they're out of stock or what. I'll do a little more digging. I have some of the Nielsen 34.9g coming. Looking forward to trying them out. Thanks!
 
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cahil_2 said:
You want a 75 yard pester shoot pellets. I went the slug route and had them shooting good with an A liner. Went back to pellets because they are pellet guns.
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Well that opens up a whole new train of thought. Perhaps I'd be better off at 75 yards with pellets. I'll wait and see how I do with some of the other recommendations first. If I jump on the pellet bandwagon, what is the recommended pellet and FPS for the FX M4 at 75 yards?
 
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jhinkens said:
Well that opens up a whole new train of thought. Perhaps I'd be better off at 75 yards with pellets. I'll wait and see how I do with some of the other recommendations first. If I jump on the pellet bandwagon, what is the recommended pellet and FPS for the FX M4 at 75 yards?
Click to expand...
AEA pellets are outshooting literally anything in most of my rifles. Including out of my FX slug liner! Half inch or better at 50y with the 33.9gr all day anywhere from 880 to 920 fps. That said, each gun/barrel is individual so you’ll have to try different ones as well. Not as picky as slugs though. Other doing well out of MY slug liner are JTS (they are very similar to the AEA) and JSB MK II. The regular king heavies are doing just fine as well though.
 
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greenbeans said:
AEA pellets are outshooting literally anything in most of my rifles. Including out of my FX slug liner! Half inch or better at 50y with the 33.9gr all day anywhere from 880 to 920 fps. That said, each gun/barrel is individual so you’ll have to try different ones as well. Not as picky as slugs though. Other doing well out of MY slug liner are JTS (they are very similar to the AEA) and JSB MK II. The regular king heavies are doing just fine as well though.
Click to expand...
Greenbeans, I'm seeing there are two types of AEA 33.9gr pellets on the Utah Air website. There's the 'Center Punch Diabolo' and the '.25 Diabolo Pellet Heavy (+)'. Which one are you having the best luck with? Thanks, Joe
 
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