Tuning FX Impact MK2 STX w/PP 600mm FPS dropped after cleaning barrel

[RunningBull]

I have a FX Impact MK2 STX 600mm barrel w/PP, the rifle was bought new in April 2020. I have been shooting JSB 18.13gr but wanted to try some slugs with the STX barrel. After shooting the FX Hybrids, JBS Knockouts and Javelins I removed the barrel for easier cleaning. I used only a coated wire cable with a patch eyelet. The cotton patch was lightly oiled and pulled through the barrel one time. I then ran about 15 dry cotton patches to remove the oil and slug residue. I then replaced the barrel carefully as to not damage the o-rings. Next, I removed the air bottle and drained the air pressure from the regulator. I did this so I could lower the reg pressure back down to 80-85 bars for my normal tune for the JSB 18.13. This should have put the FPS back in the 900s but when I checked using the FX chronograph I’m only getting ~750 FPS.

The power wheel preload spring is maxed and the VS knob is fully backed out; 4th line plus, and reg pressure at 130 bars is yielding only ~830 FPS. I do not hear air leaking from the tank or the regulator but it’s apparent I’m losing a lot of muzzle speed. In the past if the reg pressure was set at 130 bars the muzzle speed would be over 1000 FPS using JSB 18.13 gr pellets. My first thought was the air transfer port was misaligned; not so, I double checked. The o-rings on the barrel appear undamaged. Could the slugs have damaged the STX barrel? or am I missing something? I need some advise.



Thanks

 

[Butch]

What about your breach oring?

Butch

 

[tor47]

You say the hammer spring preload is maxed? In some cases where you have to much hammer force, the valve jumps back and close to fast, and you loose speed. Have you tried lowering the power wheel from "max" and down to "min", to see what happens? Having the hammer force maxed out for your settings, sounds to me being to much.

 

[Odoyle]

This is another reason why I never remove the barrels (or liners or shrouds) on any guns no matter what in addition to potential lost accuracy.

I would buy another Impact so i can shoot one specific for one type of slug in one and one specific pellet in the other in same caliber so never touch anything once set perfect. There are others who buy multiple Impacts to do the same so I have noticed so it's not just me. 

Slugs should not damage barrels.

In case it's your breech o-ring.

https://youtu.be/_VNognVDiak

 

[Glem.Chally]

Mk2 can be adjusted with pressure in the bottle. Just give it a 1/4 turn down or up then shoot once or twice and repeat.

The old rules for the reg don't apply to the AMP reg on impact.

 

[lenweber2]

Reset hammer spring back to where you had it. As well as the other settings.

 

[RunningBull]

Problem solved. Rookie mistake. When I installed the barrel I had the transfer port facing up. I didn’t realize there are two indexing slots at the end of the barrel and the transfer port was 180 degrees out. All is good now. Thanks everyone 

 

[bigHUN]

I just love these moments of drama with the Impacts. Instead of re-taking it apart we jump right away on the keyboard and calling all friends around a globe.

Don't worry, you will learn this to :\

move the PC upstairs to next floor and the Impact downstairs to the basement....

you will get it either in your head or in your legs



Edit: or something like that sorry if confusing but translated from lower level language