FX FX Impact M3 - I Can't Tune It to Higher Velocities - Strange ???

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Wolfy Smith

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Sep 19, 2024
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Hi there Guys - hope you're all well.

I've attempted to tune my FX Impact M3 in .25 calibre, to shoot JSB King Heavy MkII 33.95gr pellets at what is considered to be their optimum velocity of around 880 fps or so.

As I nudged up the 2nd Regulator in 10 bar increments, this is what I saw. (I did fire 5-6 shots to let the gun stabilise at the new settings each time).

Initial 2nd Reg P = 100 bar

2nd Reg P Muzzle Velocity
(bar) (fps)

100 685
110 695
120 710
130 710
140 740
150 575

I stopped there as I clearly wasn't going to get anywhere near 880 fps before hitting the 170 bar maximum 2nd Reg pressure - plus obviously the MV had actually dropped.

This is the first time I'd attempted to tune my M3 - I simply decocked the gun, then rotated the behind-trigger reg anti-clockwise to nudge up the 2nd reg pressure. I'd changed nothing else from the factory settings I've been using in the 3 years I've owned the gun. Valve adjuster at 4 lines, Macro wheel on 16 and micro thumbwheel on 3. 1st Reg is at 150bar.

I did fill the air tank to 200-250 bar before I started, and a couple of times during the 'tune' to keep the pressure topped up.

Anyone have any ideas what's happened / happening / what I've broken ? There is no air loss or anything obviously wrong / damaged about the gun before / during / after - I'm just at a loss as to why I can't get the MV up. I wasn't expecting to reach 3500 fps or anything, but I should be able to get to 800-900 fps.

But as it's my first tune, I've no direct experiance to know if MV increases of 10-20 fps per 10 bar of 2nd reg pressure is typically what you see.

Any ideas please, anyone ?

Thanks Sean
 
What you want to do is:

Open valve adjuster aaaaaall the way. Crank hammer to max. Now shoot. If too slow adjust pressure (better in 5b than 10b increments). Shoot again. Repeat until you get to ~102-103% of your target speed, meaning 10-20 fps more than you want. If your speed starts dropping at some point in this process your hammer and spring can’t do more pressure and your maxed out at that point. If you reach the 102-103%, start dialing the hammer back until your just a hair over target speed, like 5-10 FPS over. Now start closing valve adjuster until you hit target speed. You should take at least 5 but petter 10 shots after every adjustment to let things settle and consider the last few shots as the official “measurement”.
 
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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.
 
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CrashKT said:
  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.
Click to expand...
To each their own, but I wouldn’t start at 50b if o would want to shoot 34gr at around 880-900 ;) also setting hammer in the middle as starting point will leave you guessing as to where valve lock starts…
 
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CrashKT said:
It's easier to go up than down. Trying my way should avoid valve lock.
Click to expand...
You can’t avoid valve lock though, he doesn’t even know whether he can make 880-900 with 34gr with current spring and hammer. All we know is that right now he is valve locked between 140 and 150b with current hammer. Going up with pressure with hammer somewhere in the middle doesn’t avoid valve lock, it might give you the wrong idea as to where you’re locked though. It’s pretty simple, valve lock is the pressure at which your MAX hammer can’t overcome the pressure anymore… to find that spot, you need MAX hammer…
 
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greenbeans said:
You can’t avoid valve lock though, he doesn’t even know whether he can make 880-900 with 34gr with current spring and hammer. All we know is that right now he is valve locked between 140 and 150b with current hammer. Going up with pressure with hammer somewhere in the middle doesn’t avoid valve lock, it might give you the wrong idea as to where you’re locked though. It’s pretty simple, valve lock is the pressure at which your MAX hammer can’t overcome the pressure anymore… to find that spot, you need MAX hammer…
Click to expand...
There is no way he should be at valve lock. unless there is info we dont know.
 
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Leave your reg right where it is. Open the valve knob to just above 4 lines and start increasing the micro wheel up from 3 In two to three click increments. You will find your velocity. There is a very large difference between 3 and 3.5 on that scale. Going to 4 or over 4 on the scale wont hurt a thing.
Reason I say leave the reg alone is that for now it is more important for you to see the interaction of the hammer with the plenum pressure. Developed an understanding of how these things interact and affect each other.
Then follow greenbean’s advice. I start with my reg lower and my hammer and valve knob basically maxed out. Then the only adjustment you will be making is with the reg pressure. I like to get the velocity about 5-8% over my target velocity then back off the hammer until I am within about 10 fps over my target fps and take that out with the valve knob. From that point you can fine tune until you go crazy.
 
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greenbeans said:
You’re valve locked. Not enough hammer to overcome the reg pressure. Need more hammer spring and/or heavier hammer. What barrel length do you have?
Click to expand...
It's a 700mm Superior slug liner.

I'd have thought that most / all FX M3s were the same / similar out of the box. Unless there are lower power ones sold in the UK where I am ? But mine's on a Firearms Certificate, so I assume it's the same as all the other .25 cal M3s out there ?
 
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greenbeans said:
What you want to do is:

Open valve adjuster aaaaaall the way. Crank hammer to max. Now shoot. If too slow adjust pressure (better in 5b than 10b increments). Shoot again. Repeat until you get to ~102-103% of your target speed, meaning 10-20 fps more than you want. If your speed starts dropping at some point in this process your hammer and spring can’t do more pressure and your maxed out at that point. If you reach the 102-103%, start dialing the hammer back until your just a hair over target speed, like 5-10 FPS over. Now start closing valve adjuster until you hit target speed. You should take at least 5 but petter 10 shots after every adjustment to let things settle and consider the last few shots as the official “measurement”.
Click to expand...
This was what I was trying to do - but I couldn't get to 102-3% of my target speed in the first place. It seems the gun just won't get there, which is odd because nobody in all the posts or tutorials I've read and watched even mention the possibility an M3 can't get to 800-900 fps. As I said, I'm not trying to get to 3500 fps - my M3 should be able to do 800+ fps without modification, surely ?
 
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Chukar60 said:
Leave your reg right where it is. Open the valve knob to just above 4 lines and start increasing the micro wheel up from 3 In two to three click increments. You will find your velocity. There is a very large difference between 3 and 3.5 on that scale. Going to 4 or over 4 on the scale wont hurt a thing.
Reason I say leave the reg alone is that for now it is more important for you to see the interaction of the hammer with the plenum pressure. Developed an understanding of how these things interact and affect each other.
Then follow greenbean’s advice. I start with my reg lower and my hammer and valve knob basically maxed out. Then the only adjustment you will be making is with the reg pressure. I like to get the velocity about 5-8% over my target velocity then back off the hammer until I am within about 10 fps over my target fps and take that out with the valve knob. From that point you can fine tune until you go crazy.
Click to expand...
Thanks - I'll give this a go.

All the tutorials and posts indicated to me that adjusting the thumbturn micro knob was more about smoothing the action of the hammer once you were at / near your desired velocity. Might adjusting it a few clicks get me from 740 fps to 880 fps ?
 
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Wolfy Smith said:
It's a 700mm Superior slug liner.

I'd have thought that most / all FX M3s were the same / similar out of the box. Unless there are lower power ones sold in the UK where I am ? But mine's on a Firearms Certificate, so I assume it's the same as all the other .25 cal M3s out there ?
Click to expand...
700mm barrel shout get you there easy. For reference here’s my M4 with 700mm .25 barrel:

Reg 130 bar
Barrel on slug port
HF pellet probe
Hammer close to max (micro a little below 4 3/4)
Valve 3.5 lines (I can measure properly but will not help for an M3 anyway)

Sends 34 grain at around 915
 
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You should be able to go beyond 880 fps with the 33.95s without changing any parts. As previously mentioned, de-gas the gun and start over. I would open the valve adjuster beyond the 4th line and start around 120 bar. If you are still nowhere near 800 fps, there's another issue at hand.

This could include a variety of things such as (listed in descending order of likelihood):
  • Incorrectly installed barrel/ liner
  • Issues with the hammer spring adjuster
  • Damage to the valve
 
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