Tuning Help with Impact M4 700mm Tune

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Dr. Fumbles

Dr. Fumbles

Member
Aug 17, 2024
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Hey everyone. I’m really struggling with my rifle and was hoping for some pointers. Feeling very frustrated and discouraged here but trying to remain hopeful.

Impact M4
700mm
.25 cal
Shooting 33.95 grain JSB Diablo Mark II pellets
Element Nexus Gen 2 optic
Impulse Air 1350 moderator

I’m having a hard time with finding a good tune. Don’t know if I’m doing something wrong or if there’s something wrong with this rifle.

This is my second Impact M4. The first one had an extreme spread of over 36. @Utah-Airguns was VERY helpful (Justin Jacobson himself even got involved to help me) and were able to confirm that they could replicate the issue on their end, but couldn’t understand why it was happening. After shipping it back to them twice and weeks of testing, they ended up just giving me an entirely new rifle to replace it. This current one has an extreme spread of 16. Do you guys think that’s still a problem or does that sound about right? I’ve now shot about 1000 rounds through this one.

At this point I’m starting to feel very frustrated and defeated with the whole process. I’ll get an impressively tight 5 shot group at 50 yards, and then the next group immediately after will be over an inch even though I made no adjustments on my end. I feel like I’m just wasting pellet, time, and money.

Does anyone have a suggested tune or a speed I should try starting off with? I feel like 888fps is good but I can’t get it to stay there since it jumps up or down so much. Any other suggestions on what to try?

(I’m cleaning every 300-ish shots, keeping my fill pressure above the reg, can confirm my parallax is set correctly, not letting anything touch the barrel unless I’m cleaning it, and wind is around 3mph or less)

At first I tried:
Reg - 120
Valve - 4.5
Macro - 16
Micro - 15 clicks under 4
Aiming for 888fps
Extreme Spread was 16
Standard Deviation was 4

It was great at first, but then the following day was a scattershot for no clear reason. So now after hours of trial and error I’m trying:
Reg - 115
Valve - 4.25
Macro - 14
Micro - 3.75
Aiming for 860-ish fps
ES and SD same as above

Is there a tune and/or speed that others have found works for them?
 
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First question is where are you buying your pellets? If you’re buying pellets on Amazon or somewhere other than one of the big retailers, there’s a good chance your pellets are at least PART of the problem. Some people go through great lengths to make sure the pellets are all the same weight and there’s no bent skirts on any of them.

Second, ES of 16 and SD of 4 doesn’t sound bad at all. When you tune, what is your process? Are you adjusting hammer until you reach the peak speed then shaving a little off the top with hammer spring and then finishing by shaving a little more off the top with the valve adjuster?

I usually tune a little faster than that, but I have a shorter barrel and shoot .22 so I don’t know if the 2 are similar, but I like to be in the 925 fps ballpark. I doubt going from 888 to 925 would make a difference, but I would lean more towards the tune not being optimal mix of regulator pressure/hammer spring/valve adjuster.

I wouldn’t be hung up on an ES of 16 and SD of 4. Sounds reasonable for that heavy of a projectile, especially if you’re not weighing and sorting ammo.

Edit: Looking at your tunes I see you have the valve at 4.5-4.25. That is nearly wide open and I suspect that is the primary reason for the inconsistency. If you like 888 I would tune to 915 or so fps, then come down a few clicks on the hammer until you are closer to 900, then start closing the valve adjuster until you drop down to 885 so you know you’re at optimal hammer AND valve. I’d assume that will tighten your fps.
 
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Floridaman2005 said:
First question is where are you buying your pellets? If you’re buying pellets on Amazon or somewhere other than one of the big retailers, there’s a good chance your pellets are at least PART of the problem. Some people go through great lengths to make sure the pellets are all the same weight and there’s no bent skirts on any of them.

Second, ES of 16 and SD of 4 doesn’t sound bad at all. When you tune, what is your process? Are you adjusting hammer until you reach the peak speed then shaving a little off the top with hammer spring and then finishing by shaving a little more off the top with the valve adjuster?

I usually tune a little faster than that, but I have a shorter barrel and shoot .22 so I don’t know if the 2 are similar, but I like to be in the 925 fps ballpark. I doubt going from 888 to 925 would make a difference, but I would lean more towards the tune not being optimal mix of regulator pressure/hammer spring/valve adjuster.

I wouldn’t be hung up on an ES of 16 and SD of 4. Sounds reasonable for that heavy of a projectile, especially if you’re not weighing and sorting ammo.

Edit: Looking at your tunes I see you have the valve at 4.5-4.25. That is nearly wide open and I suspect that is the primary reason for the inconsistency. If you like 888 I would tune to 915 or so fps, then come down a few clicks on the hammer until you are closer to 900, then start closing the valve adjuster until you drop down to 885 so you know you’re at optimal hammer AND valve. I’d assume that will tighten your fps.
Click to expand...
Thank you for the response! Lotta good info…

I’m getting my pellets from Utah Airguns. I have noticed a few bent skirts on some. I don’t weigh them, but I do visually inspect for bent skirts and separate those out.

My process for tuning seems backwards from what you described. I start off by shooting 15 groups of 5 shots, and make small adjustments to the valve for each group. I find the group that is the tightest and use that. Then I shoot 15 groups of 5 and make adjustments to the macro wheel for each group. I find the group that is tightest and use that. Then I shoot groups of 5 and make small adjustments to the micro wheel for each group. If nothing seems to work, I adjust my reg by 5 bar and start again.

I’ll give your suggestion and process a try tomorrow, thanks!
 
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Yeah the valve adjuster is the icing on the cake and should be the last thing you adjust. Let me know the results when you retune.

Set reg pressure to your “assumed” desired pressure. Find max velocity. Trim top end with macro/micro wheel until you are slightly under max velocity. Pull in the valve adjuster until you trim fat again off the max velocity.

That is the best method of tuning and sounds like it would help you a lot.
 
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I dont own an m4 but own an mk2 and m3 impact. Don't be going chasing es/sd numbers. They are just numbers. The fx impact have problems such as reg creep and sticky valve rod. Es of 16 is good. Both mine impacts left overnight ES will be at least 40-60 fps spread. I just give up on chasing tight numbers and just shoot it. Most of the time you won't see much difference unless you shooting pass 100 yards.
 
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Instead of guessing at which reg pressure and adjusting from there, set your power wheel (Macro) at half power. Then set the roller adjuster (micro) at its maximum. If the gun will not cock come down until it will then another few clicks to insure a solid cocking. Set the valve knob @ 4.5 lines.
Start with your reg low. In your case I would start at 90 bar. Test for velocity.
If you are wanting to be in the high 880 fps range, keep adjusting the reg 5 bar at a time until you reach about 920 fps. Make sure you are taking at least 10 shots at each bar level to let the gun settle in a bit.
Now start backing off the micro adjuster until you see a drop in velocity. Keep adjusting down until you get to 895 - 900 fps. Once again, fire at least 10 rounds to assure the hammer has settled.
Now go to the valve knob and start working it in until you reach your 888 velocity. You can fine tune the valve knob from there for optimum groups.
you may find that the gun and pellets prefer a different speed. Don’t be afraid to try a faster or lower speed.
by using this method you don’t have to guess at the reg pressure and there is only one direction to adjust the hammer spring.
 
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north40 said:
Not too long ago Justin (Utah Airguns) posted a great video on his tuning process. I agree with others as well. Chasing ES/SD can be a bit misleading. My .25 impact just flat out didn't like the 33 grainers. I would get okay groups but nothing like the .25 grain pellets.
Click to expand...
Out of curiosity, if I try the .25 grain pellets, what settings do you use and what speed are you shooting them? Maybe I’ll get 1 tin of those to see. I’m currently tuning at 50 yards, but I need something that I can use at 80 to 100 yards for our ground squirrels.

I’m actually about to order more pellets right now. Which ones do you use? I’ll get 1 tin or 2 to try.
 
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I'm shooting them at around 880. I don't know my settings off the top of my head and I'm not next to that gun at the moment. It's very efficient and consistent. I do know reg is roughly 100 bar. We have owned and still do own several Impacts and I can tell you that no two are the same. My dad and I have a few identical guns and the settings are never quite the same. I know it's frustrating to blow through pellets but sometimes is the only way to get where you want to be. One quick question... Have you tried for groups without the moderator attached? I love air impluse and have nothing but good things to say about them but I have learned that sometimes you gotta experiment with that too.
 
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  1. Remove bottle and degas gun.
  2. Move Macro to middle position (8) and Micro to (3).
  3. Move Valve Adjuster to right over 4th line.
  4. Set First Reg to 150 Bar.
  5. Set Second Reg to 50 bar as starting point.
  6. From here, slowly shoot and adjust your second reg a 1/8 to 1/4 turn at a time until you reach about 10 to 20 fps or so below desired FPS.
  7. Now from here use your Macro wheel to hit desired Fps within 5 to 10 FPS.
  8. Once you are in that 5 to 10 FPS range, use Micro Wheel to make with in 5 FPS or so more consistently.
  9. Now, once at FPS needed, SLOWLY turn Valve Adjuster IN (1/8th or LESS) to further add to consistency. YOU SHOULD NOT HAVE TO TURN IN MORE THAN HALF OR SO.
This is my way of doing it. My reasoning is to let the reg do 90% of the work and then use Macro and Micro so finalize it. Don't worry about numbers just accuracy.
 
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Welp. Spent quite literally the whole day today tuning. Hundreds and hundreds and hundreds of pellets. Followed the processes described here. It seems that either 860-ish or 890-ish is where I’m seeing the best groups at 50 yards. Once I move back beyond to the 75 or 85 yard range…eh. Not great at all. I would absolutely be missing a lot of ground squirrels with this dang thing.

Kinda hate PCP’s right now. Probably need to take a break for a day or so from it and try again later.
 
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Dr. Fumbles said:
Welp. Spent quite literally the whole day today tuning. Hundreds and hundreds and hundreds of pellets. Followed the processes described here. It seems that either 860-ish or 890-ish is where I’m seeing the best groups at 50 yards. Once I move back beyond to the 75 or 85 yard range…eh. Not great at all. I would absolutely be missing a lot of ground squirrels with this dang thing.

Kinda hate PCP’s right now. Probably need to take a break for a day or so from it and try again later.
Click to expand...
Maybe don’t focus so much on groups and just properly tune the gun to the ammo. Shoot faster…a 700mm barrel is capable of so much more. You shouldn’t be so focused on shooting groups at 50 yards if you don’t plan on only shooting groups at 50 yards. Get the pellet going into the low to mid 900s first. Optimally tune the gun to the ammo, not to paper.

You went from being worried about standard deviation and spreads to groups at 50-80 yards in a day?
 
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I was struggling with doing that. It seems that I can’t get the speed much higher than 908.

For example, my speed would be around the 870 range. I moved my macro wheel up 1 and my speed would go down (I would do several shots to confirm). I’d back off on the macro wheel and try the micro wheel (2 or 3 clicks), and same issue. I moved my Reg up…and my speed would still go down. At one point I had the reg up to 150 just to see and still no luck.

Valve was at exactly line 4. I was trying to wait messing with that until the end. Fill pressure was kept above the reg.

What am I missing here? How do I get it to shoot faster? My assumption is lighter pellets, but is there something else I should try?
 
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Dr. Fumbles said:
I was struggling with doing that. It seems that I can’t get the speed much higher than 908.

For example, my speed would be around the 870 range. I moved my macro wheel up 1 and my speed would go down (I would do several shots to confirm). I’d back off on the macro wheel and try the micro wheel (2 or 3 clicks), and same issue. I moved my Reg up…and my speed would still go down. At one point I had the reg up to 150 just to see and still no luck.

Valve was at exactly line 4. I was trying to wait messing with that until the end. Fill pressure was kept above the reg.

What am I missing here? How do I get it to shoot faster? My assumption is lighter pellets, but is there something else I should try?
Click to expand...
 
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Dr. Fumbles said:
I was struggling with doing that. It seems that I can’t get the speed much higher than 908.

For example, my speed would be around the 870 range. I moved my macro wheel up 1 and my speed would go down (I would do several shots to confirm). I’d back off on the macro wheel and try the micro wheel (2 or 3 clicks), and same issue. I moved my Reg up…and my speed would still go down. At one point I had the reg up to 150 just to see and still no luck.

Valve was at exactly line 4. I was trying to wait messing with that until the end. Fill pressure was kept above the reg.

What am I missing here? How do I get it to shoot faster? My assumption is lighter pellets, but is there something else I should try?
Click to expand...
Well I’m not exactly sure but I’d be happy to try to help you find whatever it is that you are missing.

It’s possible to move the reg up to 150 and still drop speed if you didn’t increase the hammer (macro/micro wheel). When you increase the reg pressure you will also need to increase the hammer because you will need more force to hit the valve to fully open it.

There’s a reason why you have to follow a specific method when tuning. You really can’t turn knobs and dials if you don’t know exactly what each turn of the dials will do. When you turn your reg up to 150 how are you turning it back down? Are you degassing the gun and lowering the reg and then starting again at the bottom? You can damage your gun if you don’t degas the gun before dropping the reg by more than a few bar.

This is why you need to find max velocity for your set reg pressure and slowly work your way up. You need to start at a lower reg pressure and find the maximum velocity and if that’s not enough then you need to increase reg pressure slowly and find your NEW max velocity for that reg pressure. If you turn up the reg and your fps goes down you need more hammer spring (or a new hammer weight if you get to that point) but you shouldn’t be shooting for groups until you tune the gun to optimal velocity first. If you tune a gun to an ammo and speed that you like then you can shoot groups and if the groups aren’t tight you need to find a new maximum velocity.

Have you indexed your barrel? This is a pretty important thing to do with fx rifles as it will directly affect your accuracy and consistency at various distances.

I can fully tune my gun from scratch with under 50 shots (and that’s a generous figure). The purpose of tuning is to test different speeds with a given ammo. You have to find the speed at which the ammo likes to perform. Watch that video again possibly and the section of the video when he’s out by the pool tuning is the most important part.

There’s really quite a bit that goes into it. I watched several videos on tuning when I was learning and you have to follow the steps. If you plan on shooting out to 80+ yards you need to get your speed up from 860 in my opinion.

Find max velocity for a given reg pressure, if it’s not fast enough you have to increase reg pressure and again find the maximum. Rinse and repeat until you are at your desired velocity.
 
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Floridaman2005 said:
Well I’m not exactly sure but I’d be happy to try to help you find whatever it is that you are missing.

It’s possible to move the reg up to 150 and still drop speed if you didn’t increase the hammer (macro/micro wheel). When you increase the reg pressure you will also need to increase the hammer because you will need more force to hit the valve to fully open it.

There’s a reason why you have to follow a specific method when tuning. You really can’t turn knobs and dials if you don’t know exactly what each turn of the dials will do. When you turn your reg up to 150 how are you turning it back down? Are you degassing the gun and lowering the reg and then starting again at the bottom? You can damage your gun if you don’t degas the gun before dropping the reg by more than a few bar.

This is why you need to find max velocity for your set reg pressure and slowly work your way up. You need to start at a lower reg pressure and find the maximum velocity and if that’s not enough then you need to increase reg pressure slowly and find your NEW max velocity for that reg pressure. If you turn up the reg and your fps goes down you need more hammer spring (or a new hammer weight if you get to that point) but you shouldn’t be shooting for groups until you tune the gun to optimal velocity first. If you tune a gun to an ammo and speed that you like then you can shoot groups and if the groups aren’t tight you need to find a new maximum velocity.

Have you indexed your barrel? This is a pretty important thing to do with fx rifles as it will directly affect your accuracy and consistency at various distances.

I can fully tune my gun from scratch with under 50 shots (and that’s a generous figure). The purpose of tuning is to test different speeds with a given ammo. You have to find the speed at which the ammo likes to perform. Watch that video again possibly and the section of the video when he’s out by the pool tuning is the most important part.

There’s really quite a bit that goes into it. I watched several videos on tuning when I was learning and you have to follow the steps. If you plan on shooting out to 80+ yards you need to get your speed up from 860 in my opinion.

Find max velocity for a given reg pressure, if it’s not fast enough you have to increase reg pressure and again find the maximum. Rinse and repeat until you are at your desired velocity.
Click to expand...
You sir are a saint. Thank you for trying to help me.

Due to something else I ended up not going into work today. So I have the day off and will try it again once more. I have about 600 Pellets left at this point. I ordered more yesterday but they’ll be here tomorrow or the day after.

I’ll read over this again and try once more today. I’ll also watch that other vid once more before trying.

Yup, degassing the gun if I’m going down more than a few bar at a time.

There was a video by Utah Airguns where they went over their tuning process. In that video, they explained that you start off with low reg pressure and dials set to the middle and work your way up one click at a time. Once the velocity drops, go back 1 click and bump the reg up and continue. I thought I was doing that. But no matter how many clicks I moved up after bumping the reg up, it would still drop unless I went down on that wheel. Very confusing.

I don’t believe I’m familiar with indexing the barrel. I’ll have to look that up.

Edit: I just watched some vids on barrel indexing. I can confirm that when I shot at 50 and then 75 and then 85, my shots were dropping straight down as I went further back. They didn’t go off to the side at all. I believe Utah Airguns already indexed it before shipping it out to me.
 
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Dr. Fumbles said:
You sir are a saint. Thank you for trying to help me.

Due to something else I ended up not going into work today. So I have the day off and will try it again once more. I have about 600 Pellets left at this point. I ordered more yesterday but they’ll be here tomorrow or the day after.

I’ll read over this again and try once more today. I’ll also watch that other vid once more before trying.

Yup, degassing the gun if I’m going down more than a few bar at a time.

There was a video by Utah Airguns where they went over their tuning process. In that video, they explained that you start off with low reg pressure and dials set to the middle and work your way up one click at a time. Once the velocity drops, go back 1 click and bump the reg up and continue. I thought I was doing that. But no matter how many clicks I moved up after bumping the reg up, it would still drop unless I went down on that wheel. Very confusing.

I don’t believe I’m familiar with indexing the barrel. I’ll have to look that up.

Edit: I just watched some vids on barrel indexing. I can confirm that when I shot at 50 and then 75 and then 85, my shots were dropping straight down as I went further back. They didn’t go off to the side at all. I believe Utah Airguns already indexed it before shipping it out to me.
Click to expand...
Also dont be scared to try other brand of pellets
 
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