Tuning Tuning my Impact for the first time, could use some help...

[Stretch]

I bought a new (refurbished) FX Impact Mk II (probably should call it a Mk II.5) in .25 caliber with 700mm barrel and power plenum. It was delivered shooting JSB 25 grain pellets at about 910 fps and 34 grain at about 750 fps. Original settings were regulator at 100 bar, front valve setting at about 2 1/2 lines and hammer spring about 1/2 way.

I want to tune it so it shoots 34 grain pellets at about 880 fps. I've watched a couple videos on tuning, but to be honest, it was pretty confusing. So I searched for other people's settings and found one person had the regulator up to 120 bar, hammer spring at max and front adjuster at 4 lines. I tried that and the 34 grains were flying at over 1,000 fps. I'm guessing that person didn't have a power plenum.

So, I left the hammer spring at max and cranked down on the regulator until it was back at 100 bar. I then tightened the front valve adjustment until the 34 grains were shooting at 880 fps. It's now at about 3 lines. I shot 6 rounds and the speed seemed pretty constant (varied from 880 to 886).

I'm guessing that keeping the hammer spring at the max, the front valve adjustment as tight as will work and the regulator at the lowest pressure that will work, I'm using air efficiently. Am I doing this right or is there something I should be doing differently?

 

[madeintheuk]

You’re on the right path. Only thing I’d add is to back off on the hammer spring until your velocity starts to drop, then that’s your sweet spot for efficiency. 

 

[Stretch]

You’re on the right path. Only thing I’d add is to back off on the hammer spring until your velocity starts to drop, then that’s your sweet spot for efficiency.

So am I right in thinking the front valve adjustment should be in as much as possible? That keeps the valve open as short a time as possible?

 

[madeintheuk]

You’re on the right path. Only thing I’d add is to back off on the hammer spring until your velocity starts to drop, then that’s your sweet spot for efficiency.

So am I right in thinking the front valve adjustment should be in as much as possible? That keeps the valve open as short a time as possible?

As long as you’re getting the velocity you want, then it has been said that a shorter, faster burst of air is more accurate than a longer, slower burst. 

 

[177er]

There are plenty of tutorials and posts on this, but the steps would be

1. Set reg pressure to your 'rough speed' - say 100 bar
2. Set Hammer preload to lowest, but the power wheel to max.
3. Set valve opening to high - 3 to 4 lines.
   [/LIST=1]
   
   • Now, start tuning the hammer spring till you get no more velocity increments and then back off by 3 quarter turns.
   • Start dialing in the valve adjuster till you get some FPS reduction.
   • This is the optimal tune, velocity and air usage for that reg pressure for that grain of pellet. You'll find this very easy to do once you start practicing.
   • Edited Note - for heavier calibers, you want to go from highest hammer spring preload with the wheel at Max. When the wheel no longer turns, turn in the spring adjustment a couple turns till you can.
   
   I might also point you to Matt's excellent tutorial.
   https://www.youtube.com/watch?v=vaeGVbasD7Q
   
   Airbuks - also shows lower power tune.
   https://www.youtube.com/watch?v=yHP4RCy7Vpg

 

[Stretch]

Awesome info, thanks very much!

 

[Glem.Chally]

Make sure if you're lowering your reg that you're turning it 1/4 turn or so then shooting a couple shots. Repeat till you're at where you want to be.

 

[177er]

Make sure if you're lowering your reg that you're turning it 1/4 turn or so then shooting a couple shots. Repeat till you're at where you want to be.

Yes - cannot be overstated.
Read the manual first. Look at all the tuning videos you can before playing with the reg.

The FX AMP reg goes up (anti clockwise), without problems and you can do down too (clockwise 1/4 turn of the reg screw), fire 1-2 shots at min power wheel, and keep tuning.