Having trouble tuning my .30 impact.

Forums Industry Q&A Having trouble tuning my .30 impact.

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    Grabagun
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    Hello, since i got such great feed back with my last question. I thought I would put this one out there for more good advice. Had my .30 fx impact mk2 700mm barrel  tuned and shooting the jsb 50 grn pellets at 890 fps. I recorded the tune and removed the barrel. Shot it in .22 for a couple of thousand rnds. When i put the .30 barrel kit back on and returned it to the same reg setting hammer spring setting and valve setting. With the same settings i am now not able to get any more than 840 fps max. Extrem spred of 80fps. Originally i was getting 920fps then tuned it down to 890fps via valve stop adjuster. Extreme  spread 10 fps. 150 bar at reg hammerspring wide open. Valve stop 3.5 lines.                      Question is.what might be causing the loss in power? Or what the hell am i doing wrong. Or could i have a leak somewhere?

    Thanks

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    Digger25
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    Is your tank holding pressure over 24 hours?

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    Ranin
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    Align the barrel with transfer port

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    biohazardman
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    Unless you measured your valve adjuster with a caliper before you changed it for the .22 the chance you got it in the same exact place may be questionable.  I would go with turning it out another half to three-quarters of a turn and see how things go from there.  Also there is usually a tiny bit of play in the barrel you may want to mess with it a bit to see that things are well centered and in their correct spot for full flow. If there is a leak and the pressure does not go down over 24 hours as Digger25 states there is a chance it could be the  breech seal, the o-ring inside of the barrel.  I noticed some inconsistencies in my velocity and when I checked my breech seal it was looking pretty nasty. So, I replaced it but have not got out to the range to check and see if things are better yet. A couple of clicks on the hammer spring dial would also cause the velocity change. If none of these are the problem your C3 bumper o-ring could just be starting to go or your hammer seat may be backing off of the valve rod.  So I guess there are lots of things to check.

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