Tuning FX Impact MK2/PP Compact in .25, speed range for Kings?

[madmunki]

I bought a FX Impact MK2/PP Compact (500mm) in .22, and converted it to .25, 500mm barrel. 
What speed range should the .25 Kings be shooting at for best accuracy at 100yds?

 

[Glem.Chally]

850-880

 

[madmunki]

Thanks. From reading on tuning, I’ll adjust to 890, and go down from there until I find the best group. 

 

[madmunki]

I adjust hammer spring to max, and air flow valve was already maxed (4+ bars). 


I degassed, and dropped regulator to 100 bar. 


from there, I increased the reg pressure until I was getting around 970 FPS. Reg at 140 bar


started turning down hammer spring until FPS dropped ~20 bar. 


turned air flow valve down until FPS dropped ~15. 


now on max I get 953, and min just under 800. This should cover the suggested 850-880 range.


Tomorrow is range day, time to shoot groups at each power setting to find the sweet spot. 


I made this little spreadsheet to track tuning. 

 

[tor47]

Seems like a good starting point. I personally do not like to max out my hammer first, as in some cases it might lead to decreased speed if the valve bounce back to fast. And also to be on the safe side, in case I am worried about damaging anything. I use the Ernest Rowe method to tune for max speed https://www.youtube.com/watch?v=9K9uG2KOPt0&t=341s. But the end result seems to be the same.

 

[madmunki]

After today’s session, shooting all the settings, hammer knob on level 2 yielded the best results. 

 

[tor47]

Thats a good group, what range is it?

 

[madmunki]

30yards. It’s where I’ll zero at. 

 

[tor47]

Thats nice

 

[qball]

Where are you on the HS? You don’t need 140 bar reg pressure to shoot kings at 900fps. With even 500mm barrel I’m guessing you can get to 900 FPS with no more than 100 bars at reg. Watch Ernest rows video and you will find your sweet spot to shoot the Kings quiet and smooth with a ton of shots. Key to reg and HS balance is finding that sweet spot which is just under the max speed for given regulator pressure then back off half a turn on the HS Allen screw on max. Then Reduce the valve a little so the speed drops about 20fps.....then listen to the gun and turn down the HS till you don’t hear the Psssssstt, just a thud and hammer noise. Hopefully that’s your target speed, if too low then increase reg by 5 bars at a time. That’s your impact happy place with lots of shots, quiet, little vibration and most importantly most consistent and accurate. 


btw if you want 100 yard accuracy then try 34 grain King’s heavy at around 860 FPS, they buck the wind better then the 26 grain kings exact. 

 

[madmunki]

Hammer Spring was wide open, until after adjusting reg pressure, starting at 972fps, I lowered HS until FPS started to drop about 10–15 FPS. I then closed Air Valve until FPS dropped again, 10-15 FPS. On MAX setting, I’ll get around ~952 FPS with the Kings. 

 

[qball]

Hammer Spring was wide open, until after adjusting reg pressure, starting at 972fps, I lowered HS until FPS started to drop about 10–15 FPS. I then closed Air Valve until FPS dropped again, 10-15 FPS. On MAX setting, I’ll get around ~952 FPS with the Kings.

what I meant by HS measurement is the little space between the frame and the HS adjustment block. 

 

[madmunki]

I have 16.63mm measuring the space. 

 

[qball]

I have 16.63mm measuring the space.

With power wheel on max? 

 

[madmunki]

Yes. 

 

[madmunki]

When I did my first tune, I started with max (140bar), and worked down from there. Taking the advice from this forum, and the FB page, I started over. Adjusting to 100 bar, hammer spring on min (just above where Min and 1, changes) and valve on max. From here adjusted hammer spring until turns stopped improving FPS, then added a little more reg, etc. following Ernest example, and got my 900 FPS back, with 110 bar, and little hammer spring. Very happy with this start of a tune, thanks everyone for the input!

 

[qball]

When I did my first tune, I started with max (140bar), and worked down from there. Taking the advice from this forum, and the FB page, I started over. Adjusting to 100 bar, hammer spring on min (just above where Min and 1, changes) and valve on max. From here adjusted hammer spring until turns stopped improving FPS, then added a little more reg, etc. following Ernest example, and got my 900 FPS back, with 110 bar, and little hammer spring. Very happy with this start of a tune, thanks everyone for the input!

awesome! Glad you found a good tune for your impact. 


sorry I got distracted today but here is my setting for reference and you are pretty close to what I have. my impact has 700mm .25 superior heavy with reg set at 100 even, hammer on max measures 16.5 and valve on 3 lines. On Max I clocked the 26 grain hades(should be about the same speed) at 955 and on min i clocked 750. Given my barrel is 200mm longer my setting will net you about 850fps with 500mm barrel so 110 bars and similar HS should get you the 900fps you are looking for. Way to go! 

 

[madmunki]

Thanks for your help qball, You were a factor in my decision to retune. I’ll test groups tomorrow. 

 

[Ginuwine1969]

Qball, my MK2 with PP, 600mm slug liner, .25 cal is pushing 34 grains @878 FPS Reg 133, VS 8.33mm, HS 26.59, PW A. Sounds a little loud think I should retune. I’m right about an MOA @ 100 yards.