FX Impact creeping velocity

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Teaboy

Member
Dec 15, 2018
17
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Lancashire, United Kingdom
Hi guys. Nice to be part of this forum.

Thought I would ask this question in this forum as you have far greater experience of tuning the FX Impact than the UK forums. Our sub 12 law stops the tinkering. That being said I've had issues with velocity creep for some time and decided to sort myself rather than ship out for weeks for possible repair.

Did a chrony string yesterday, and it typical for this rifle, first few readings were (177 cal an 8.4g pellet) 721, 741, 765 then after a 2 dozen shots it was up to 776, 782, 783 then after another 2 dozen shots it's 792, 795, 794. From experience if I had kept going it would have kept increasing, and 803 ft/sec for this combo is illegal level in the uk. That's an extreme spread of 74 ft/sec, no good.

From your guys experience do you ghink this is this a tune issue or is there a mechanical fault, possibly the regulator?

Cheers

Teaboy
 
Two possible scenarios come to my mind. Reg creep, where the valve is harder to open after the rifle sits for a period, and then becomes easier the more you shoot. You can effectively hit 800 fps without exceeding 12 ft/lbs with the 8.4 grains, so Ideally that rifle would be tuned right around 790-800 IMO. Do you have a gauge that reads regulated pressure that can confirm this is happening or not?

Alternatively if you shoot until the pressure drops below reg set point, you could experience a rise in velocity due to the valve becoming easier to open. Its less likely the case though I'd imagine.


I am sure others may chime in with other possibilities for you to consider. GL 
 
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You tube AEAC impact tune video. Set your gun up exactly as instructed. Then youll know where to start.  The impact has several adjustments.  Dont just jump in and crank on things. Any tech will tell that you start at the beginning of the diagnostic tree and go step by step, in order, and dont skip any. Good luck,
 
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DO THIS AFTER PROPER SETUP CONFIRMATION (like Keyman said)

FWIW - I read about having to rebuild your regulator every 5-15k shots a few weeks ago. I have run about 12k through my impact X and figured I would wait until it was symptomatic. Turns out that was this weekend. The first shot through was super slow - 600 fps - then it would climb immediately back up to 920. I rebuilt the regulator as Ernest prescribes in his Masterclass videos using O-Rings found through this forum.

Fx Impact/Impact X O-Ring List with Links for Purchase



FX Masterclass on Disassembly:

https://youtu.be/TjLeO7O8DA0





FX Masterclass on Regulator Rebuild Pt1

https://youtu.be/FOlG19kTf6Y





FX Masterclass on Regulator Rebuild Pt2

https://youtu.be/GD5UlmL7E_I





Whole Process took about an hour. Really pretty simple. While I was at it, I replaced the barrel orings, both inside and out. Put it back on the Chrony and dialed it back in after tightening the hammer spring tensioner. Back at 920 FPS with a SD of 4.
 
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Whilst waiting for the o rings to arrive I decided to start the regulator disassembly .

The valve rod shows signs of being adjusted down whilst under pressure. Before I removed the anti tamper I read up extensively on what to do and what not to do and I'm sure the dimple was not done by me. I removed the anti tamper so I can only assume it was shipped from the factory that way. The creep has been present since new so maybe?

1545067174_17614647175c17daa61b0721.28905424_Reg.jpg

 
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Whilst waiting for the o rings to arrive I decided to start the regulator disassembly .

The valve rod shows signs of being adjusted down whilst under pressure. Before I removed the anti tamper I read up extensively on what to do and what not to do and I'm sure the dimple was not done by me. I removed the anti tamper so I can only assume it was shipped from the factory that way. The creep has been present since new so maybe?

Click to expand...

That's the regulator piston. The valve rod is a totally different part of the gun. What was the "anti tamper"? I don't recall any on my Impact.
 
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Is your impact a first generation? (Two piece cheek rest, no number stamped under the trigger block) If so I would replace the adjuster screw as well as the delrin piston, The original ones were pointed and have now been changed to a domed to prevent this happening.



Alternatively Huma regs have a metal piston and a delrin insert between piston and adjuster and also comes with spares,

Just check they have the right one for the reg version you have
 
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Make sure you did not over loosen the valve control knob.... I did that once when I lost track during tuning and had the valve control knob backed way out and it exhibited behaviors similar to what you described above - reg was not creeping, power loss, velocity all over the place, etc....

Caused me 3 hours before I finally caught on and turned the valve control knob in and checked my velocity shot by shot as i turned it back to the original setting and got my speed and consistency back.

From my experience, contrary to what many have mentioned, the valve control knob cannot be turned "all the way out".....
 
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I initially followed some videos which said that to get maximum power, you turn the valve knob outwards. Between playing with reg pressure settings, hammer spring, and valve knob, i turned the valve knob out too much without knowing. my velocity dropped like crazy and was all over the place, creeping velocity, etc... like what you described... I initially thought it was o-ring, reg issues, etc, wasted lots of time and pellets without solving the problem.

Eventually, i found some post online that said if you backed out the valve too much, you lose power and consistency. So as a last resort before sending it back to FX, i shot over the chrony and started turning back the valve knob clockwise - viola, velocity started going higher. I ended up back at factory settings of about 3 lines for the valve knob.

Hope this helps.


 
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Hi frank320

Did you watch for velocity drop as you turned the valve in or did you look for consistency ?

Interested in how you solved the problem.

Cheers
Click to expand...

Great question. I just sent FX USA the following question:

Assuming I am shooting at the velocity I want, should I then:

1) adjust the valve control knob clockwise/inwards until till velocity drops, then back off?

or

2) adjust the valve control knob counter-clockwise/outwards till velocity drops, then back off?

I will update back here with their response once they get back to me.


 
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