Tuning FX Impact Mk2/M3 - slower first shot - no reg creep - quasi-scientific analysis

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Sure, we are all here to make the gun better.

I truly believe that the following items contribute to the issue:

-PUR90 oring and its increasing stiction,

- extrusion of mentioned oring,

- stiff valve return spring,

- delrin valve poppet.

Some combinations of them amplify the issue more. Given Impact valve design we cannot eliminate the problem entirely. We can just minimize it to the insignificant level.

In my opinion the following should be done to achieve the highest consistency possible when it comes to the first shot after valve inactivity time (most important comes first):

- peek backup washer should be installed to prevent from oring extrusion,

- PUR90 oring should be replaced with NBR90/80 or Viton90/80 (the latter one may not be good enough abrasion resistance wise but it has the lowest stiction among three mentioned compounds),

- peek valve poppet should be installed,

- valve return spring should be balanced - not too stiff and not too weak. The original spring seems to be more one a stiff side. The Huma power kit one is too weak unless you have 700mm barrel.

@mubhaur, what is the specification of the valve return spring which you find optimal?
 
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Sure, we are all here to make the gun better.

I truly believe that the following items contribute to the issue:

-PUR90 oring and its increasing stiction,

- extrusion of mentioned oring,

- stiff valve return spring,

- delrin valve poppet.

Some combinations of them amplify the issue more. Given Impact valve design we cannot eliminate the problem entirely. We can just minimize it to the insignificant level.

In my opinion the following should be done to achieve the highest consistency possible when it comes to the first shot after valve inactivity time (most important comes first):

- peek backup washer should be installed to prevent from oring extrusion,

- PUR90 oring should be replaced with NBR90/80 or Viton90/80 (the latter one may not be good enough abrasion resistance wise but it has the lowest stiction among three mentioned compounds),

- peek valve poppet should be installed,

- valve return spring should be balanced - not too stiff and not too weak. The original spring seems to be more one a stiff side. The Huma power kit one is too weak unless you have 700mm barrel.

@mubhaur, what is the specification of the valve return spring which you find optimal?
Click to expand...

Seeker with the viton oring and peek poppet and the peek backing washer you have the combo to solve the problem 8 fps could be difference of pellet weight or many other factors the testing I would be doing now with that combo would be seeing how long the viton oring lasts before it needs replacement I've had good luck running viton in other situations I would shoot the heck out of it and see how long before it would need to be changed then go from there just my opinion on it
 
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I agree with you that three items which you enlisted should be sufficient.

I just did one more test:

- original valve poppet,

- peek backup washer,

- viton80 PowerPlenum oring,

- original, strong valve return spring.

I set the gun to 247m/s, way below plateau. After 24 hours the following shots were:

246, 246, 247m/s.

I think it is a success of this modification.
 
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I agree with you that three items which you enlisted should be sufficient.

I just did one more test:

- original valve poppet,

- peek backup washer,

- viton80 PowerPlenum oring,

- original, strong valve return spring.

I set the gun to 247m/s, way below plateau. After 24 hours the following shots were:

246, 246, 247m/s.

I think it is a success of this modification.
Click to expand...

To me its as below 

Peek internal part to eliminate extrusion

A bit lighter valve spring 

A bit heavier hammer weight

NBR 90 shore plenum O ring

Proper tuning of the gun

Bhaur
 
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I am (I was, last year) using a light valve spring, but in Jan replaced the hammerspring.

Couple days ago finally I got some free time and let me tune the .25 Impact MK2 for 41gr slugs, and of course I blew the 2mm valve oring. Last time I didn't put a rubber ball in front of C1.

Last night deep surgery on the plenum, I replaced all the orings, and once there a devil told me to refresh the PUR90 as well.

When I assembled all and now want to set the C1.... omg how hard to moove the valve rod now with a new PUR90...hoping will wear out soon, this may no bueno for finetuning slugs. Only good I have made my MK2 a monster power for shooting 44 and 46 expecting around 950 ish.
 
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Place NBR90 there instead of PUR90. All this thread and it seems you make the old mistakes which makes me sad.
Click to expand...

On page #4 (I think) you scroll to the middle and look for my avatar thingy... I said that my dealer sent me .. based on...he knew several ppl putting NBR90 instead of PUR90. And that he was relating to last year...

Anyway, my original PUR90 had about 10K shots on it and it was a time to swap. I am not going back there only at the next crash.

I am not hunting, a first (one or five or ten) shots at the bench really doesn't make much of a excitements. I need a better weather outside to test what and how my heavy upgrades will behave with the C1 = valve rod, maybe a bigger moment of inertia will over ride the friction on the cold PUR oring ??? will see


 
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Place NBR90 there instead of PUR90. All this thread and it seems you make the old mistakes which makes me sad.
Click to expand...

On page #4 (I think) you scroll to the middle and look for my avatar thingy... I said that my dealer sent me .. based on...he knew several ppl putting NBR90 instead of PUR90. And that he was relating to last year...

Anyway, my original PUR90 had about 10K shots on it and it was a time to swap. I am not going back there only at the next crash.

I am not hunting, a first (one or five or ten) shots at the bench really doesn't make much of a excitements. I need a better weather outside to test what and how my heavy upgrades will behave with the C1 = valve rod, maybe a bigger moment of inertia will over ride the friction on the cold PUR oring ??? will see

Click to expand...

It helps if you increase the hammer weight and restrict the valve travel from valve adjuster. The extra inertia over powers the sticking of O ring and valve adjuster doesn't allow to generate more power than desired. 
 
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Place NBR90 there instead of PUR90. All this thread and it seems you make the old mistakes which makes me sad.
Click to expand...

Seeker did the viton hold up still or did u go to nbr90 already
Click to expand...

I have over 600 shots with the Viton in my gun. No problems yet.
Click to expand...

Good to hear I'll probably use viton then since I have some on hand 
 
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