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FX Impact should I enlarge .25 TP ?

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AirSupply

AirSupply

Member
Jan 12, 2017
1,419
293
Victoria, Australia
I have an Fx Impact and really like the gun. Originally purchased it with the .22 barrel but was always keen to have .25 cal and ordered that the day I bought it. 
The .22 was the last one they had so I took it. In .22 it totally lived up to my expectations. I really enjoy shooting it that way. I always hoped the .25 would be all the .22 is and more!
In .25 I'm not getting the velocity to fully explore the limits of where others have found real stability and accuracy. 
Im able to shoot the normal kings at just around 900fps max and the heavys at 800fps.
They Shoot ok at this speed but still not quite as good as the .22. 
I have stripped the gun completely and rebuilt it with all new orings and all seems to be working as it should. 
I have experimented with reg pressure from 135 to 150 bar but still maxing out at same numbers. 
Decided it could be the hammer spring and have ordered a new one. (Taking for ever).
So I'm thinking of enlarging the transfer port by .5mm. 
It seems to be stock at 5mm and feel confident I could drill it out to 5.5mm. I understand there is more to doing this job properly that just running I drilling through.
Is this a good Idea? Am I going to have loading issues with the pellet dropping and scuffing if I increase the TP .5mm 
Has anyone enlarged the TP and did it help increase velocity. 
Did it cause loading issues? 
Thanks Michael

 
Hi hci, I just ordered the part from our fx dealer here in Australia. I don't have the gun apart at the moment but someone else may have the specifications of the spring and be able to help you. 
Interesting your gun lost power from being left cocked. I'm hoping my new spring will arrives soon. 
If leaving your gun cocked for a day made that much difference I should leave the TP till I'm sure 
its not the spring. 
Im thinking I should have just ordered the spring from AOA who I'll bet has them in stock. 
Maybe you should do that. 
Michael



 
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"greenanchor"If you do decide to enlarge the port I think the best way is to enlarge it into an oval, less chance of it causing pellet issues.
Click to expand...
Agree, I made the one of my Impact's CZ barrel 5mm wide and 7mm long. (TP in breech is about 7mm, same as the .30 barrel's TP) 
However, A Royale 500 regulated at 160 bar can push king heavies over 260m/s with a TP only 4.5mm diameter.
It seems that the TP is not the limiting factor here.
Sometimes the set screw of the power adjuster's sliding block tends to back out over time, decreasing the hammer spring tension.
Michael, you might want to check that first before making irreversible modifictions ;) Look in the impact troubleshooting guide for the right gap.
 
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Gijs I checked my power wheel set screw and
measurement. I also replaced the power wheel. All good there. My gut tells me I have a weak Hammer spring. From your info I must have some other issue 
so I'll leave the TP for now and wait for a new spring just to rule that out. 
There does seem to be some variation in the power the impact produces gun to gun. The balance between the 2 springs could be where it is coming from. 
There isn't anywhere else I can see could produce much variation if the settings are all correct. 
The other thought I had if the new hammer spring makes no difference is to cut a very small amount off the valve return spring. Is this a crazy idea?
Thank you both for your advise. 
Michael
 
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BAD idea - dont cut the return spring its only for closing valve when gun is empty.
​Bought new hammer spring.
​My .25 impact shoot king heavy 265m/s when i left cocked for 24h the spring get weak and now i cant only 250m/s so bought new or custom litte harder (5-25%) from oryginal.
​I want over the weekend dissamble my impact and go to spring factory for making oryginal and 10%/20% - stronger spring.
 
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Can't wait to see your results! I will remove my spring today. I'm sure other dementions will be the same but length could be interesting. 
I will also measure the force required to pull the valve rod forward to the point it would touch the rubber ball in the valve adjuster when it is adjusted out with 4 marks showing. 
If someone else who is acheiving good velocity did the same measurement would be great. 
Then I can relax about the valve return spring....
Apples to apples. 
I'll be back!🙃
 
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"hcl"BAD idea - dont cut the return spring its only for closing valve when gun is empty.
​Bought new hammer spring.
​My .25 impact shoot king heavy 265m/s when i left cocked for 24h the spring get weak and now i cant only 250m/s so bought new or custom litte harder (5-25%) from oryginal.
​I want over the weekend dissamble my impact and go to spring factory for making oryginal and 10%/20% - stronger spring.
Click to expand...
Why let it cocked for 24 hours ?
You fell asleep in your fround blind or,what ?
Joke
 
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Been doing some more measuring. If the valve rod travels forward over 7-7.5mm it can come out of its rear guide/seat. If the front rod measurement in the pic I posted is as recommended 6-6.5mm the valve has a max opening distance of 6mm before it hits the rubber ball in the valve adjusting knob (with max setting 4 strips). Then it can't come out. Mine at 3.5 has a theoretical max distance of 9mm So if the hammer spring was powerful enough it is possible to push the rod so far for it could come right out of the rear seat. 
I don't think the stock spring has the power to do that. Well it hasn't on mine luckily. 
So no matter what spring is used there is only 6mm
of valve travel.
This has made me think that rather than just tighten the piece on the end of the valve rod maybe it should be adjusted to the 6-6.5mm and this is why it has the grub screw in the end. (That usually falls out)


 
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New 2mm longer spring does not improve performance drastically: /
Reg. 160bar spring MAX = 270m / s on .25 heavy.
I dissamble pcp and increased to 5.4mm port in pusher and port in barrel from 5mm circle to elipse 5.4x5.1 and polish to mirror look.
On longer springs 280m / s heavy WITH reg 147bar !!!.
On the weakened original spring 265m/s :]

So the key is to modify and polish transferport !!!! in barrel nad the pusher !!!
Pellet now go in barrel silky smooth excelent :>
 
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hcl that is a great result. I enlarged the port on mine also am going to conect a better air gauge to set my regulator to 147b. I know the fx gauge is not accurate and need to get a better idea where it's at. 
My gun also now loads 'better' than it did before! Very smooth with the mk1 heavys. 
So you are getting over 900fps! How accurate are they shooting at that speed for you?
Well done!
Michael
 
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