FX Impact should I enlarge .25 TP ?

[hcl]

AirSupply - i bought 0-160bar CL 1.5 air gauge (BIG) only for settings regulator its spread is +-2.5bar :]
I shoot only mkI heavy.
I dont know how accurate are they because now the wind is very hard about 40km/h and faster so i cant shoot long range.
Now i set to about 862fps on weekend spring and in 2 mags chrono dont change none :] rocky steady on 862fps.
I want to change oring in barrel and before that polish to mirror look insade of this first 1" where is TP and place of joining brass with steel barrel.
I want to bay new spring 56mm because on my tuning 58mm i cant go under limit in my cantry for transport.
I thing that with new one i can get to 900fps with reg on about 150bar and 850fps with reg 140bar o n heavy with that modifiedy TP.

 

[GQ]

The fps from a chrony to another chrony can varry as much as 30-50 fps.
So it is very difficult to know exactly what is the real fps out of a barrel.
For example with my .25 Impact, I have an average of 880-890 fps shooting JSB MK II, 33.95 grains.
Valve with 4 visible lines.
Power wheel at 4.
Regulator showing 150 bars.
Who knows if my chrony show me the real fps ?
Impossible to know if I dont use a total of 3 different chrony to compare.
So my chrony reading is just a reference and use it to calculate my ballistic coefficient and make sure my scope tracking is 100% precise and accurate at different distances.

 

[AirSupply]

Hi GQ. I'm happy my chrony is pretty accurate. It has always been accurate in terms of giving correct outcomes when I enter velocity into Strelok and in .22 my gun is accurate at 910 915 fps which is normal. I've also tried it beside the phone app chrony and I know that's not terribly accurate but they where very close! On the whole I think if they are set up correctly there are accurate. 
I checked my reg pressure with a better quality gauge and set it to 148bar. Turns out my fx gauge is a rare one that is spot on!! 
I still don't have a new spring and so thought I would try something else. I added 1gram to the hammer. It weighed just over 19 grams now it weighs just over 20 grams. 
Over the chrony I'm now getting 860fps on max. Later when I shot some groups I was very happy. 
On power 5 shooting great groups. Still need to see what they are shooting at on power5 over chrony. Ran out of time. 
This is the first time I've managed to get above 800fsp! 
hcl thanks for your help. 
Michael

 

[Verve]

"hcl"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 :>

Did a similar mod last year on the .22 barrel.

Enlarging TP and pellet probe hole lead to a plus of 17fps on the .22 JSB Monster 25.4g from 855fps to 872fps @150b. This with a 0.5mm increase as you've done. Without the stiffer and longer spring though.

Did consider cone shaped TP (5mm inside, wider on the out) but shorter .22 FX barrel is a major limiting factor in achieving the 900+ on the JSB Monster. 24" LW barrel next.

Not tinkered with .25 TP yet. Thanks for posting your findings and will dig it out again when it's time.

 

[AirSupply]

Hi Verve, fx do make 600mm .22 barrels. That is standard here in Australia. I'm sure your fx importer could get one for you. Understand you may want the LW. Will you machine the whole length of the barrel down to 14mm from 16mm?
Other option could be the x twist barrel. 

I increased lengthways by 1mm and left width at 5mm. 
Reajusted screw on the power wheel to take out slack and getting 870fps with the .25 heavys. Think there best at 820 in my gun.