Advice Sought. Weird FX Impact behavior

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tsp3355

Member
May 13, 2015
269
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Colorado, United States
Hoping someone can point me in the right direction here without having to spend hours combing through all the FX Impact threads. My Gen 1 Impact was shooting lights out until like an idiot I decided to clean the barrel. I ran a few patches through with a small amount of gun cleaner and then a few dry patches. I didn't remove the barrel. Next trip to the range it was dead nuts on at 50 but all over the place at 100. I thought I might have opened up a bad tin of pellets, but went back to the range today with a different tin that I know is good and got exactly the same results. One hole at 50, and about 8 inches at 100 with no consistent pattern of miss. I haven't put it on the Chrony. Will try and do that tomorrow. Did a quick inspection of the barrel o-rings and they appear to be fine.

If anyone has an idea what may be going on, I would greatly appreciate your advice. Thanks in advance for any assistance you can provide!

Tracy P
 
Not 100% sure how ever it could be something with twist rates over stabilizing vs weight. Have you tried different pellet weights some twist rates and velocities do well and x speed but weird things at y speed and distance. If you had a way to check for wobble, camera or shoot targets at interval distances till you find the opening up effect. My guess it pellet weight vs twist is culprit. But like I said just my hypothesis. Matt dubber from Africa has a vid explains some of this stuff
 
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I currently have it tuned for close range pesting. I haven't shot anything other than JSB 15.89s at 850 fps for more than 2 years. Prior to me cleaning the barrel it was shooting right around an inch at 100 yards (indoors, so wind isn't a factor). Post barrel cleaning same tune, same ammo, one hole groups at 50 yards, 8 or so inches at 100. Has me baffled because its still dead nuts on at 50 and below. You could ask my local pest birds if they weren't already toast.

I've probably only put about 100 pellets through it since I cleaned the barrel, so maybe it needs more seasoning, but its so far off at 100 I find it difficult to believe that's it.
 
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I don't have an answer, but yes, it does seem weird. The chrono test should be done for sure, but I kind of doubt it will reveal a problem. If velocity was so inconsistent to produce 8" groups at 100 yards, I think something would show up at 50. The only exception I can imagine, if velocity is simply way down, but still consistent. I know these things are adjustable for power, don't suppose you accidentally got the power adjustment off? 
 
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OK. Got it on the chrony this afternoon. It had definitely lost about 30 FPS from my last testing which was about a month ago. It had gone from a very consistent 850-855 down to a pretty consistent 815-825 on a 60 shot test run. My settings for over a year have been Reg at ~120, Power wheel on low, Valve adjuster almost all the way in. Those setting produced a huge shot count of about 110 shots with an extreme spread of 7-8 fps between 848 and 855.

After seeing the change in FPS I started tinkering with the settings. Changing the power wheel initially did absolutely nothing. Zero change in FPS. So then I opened up the valve adjuster back to what I think the typical factory setting is (3rd line just visible). That brought the power back up to where with the power wheel on low velocity is consistently back in the 848 to 855 range. With power wheel on max or 5 its up to about 875 FPS. I didn't have time to run another full 60 shot string, but the velocities appear to be again in a pretty tight 5-7 FPS spread over about 30 shots.

I'm not certain what the C3 does, but I know its part of the valve rod assembly. Based on the above does this sound like the C3 needs to be replaced?

Thanks in advance for your advice!

TracyP


 
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I had a similar experience with my Raw .30. It was shooting light out. I thought it was time to clean the barrel. I did. The group open up to over 4" center to center at 100.So I shot 450 pellets through it trying to figure it. It slowly started to close the grouping down at 250pellets. About 450 pellets it was right on at 100. Back to shooting sub MOA groups. Now I only clean the barrel only when there is a grouping issue. Now I clean with a simple lubed patch and 3 dry patches. It take about 100 pellets to dirty it up the way the barrel likes.

But I'm not saying this is the same problem you have, check your breach o-ring. I also have seen 30FPS drop with my Impact when it cold out side. Try open your valve adjustment out 1/8 turn.
 
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I'm not certain what the C3 does, but I know its part of the valve rod assembly. Based on the above does this sound like the C3 needs to be replaced?

Click to expand...

Mine is a .30 and when the C3 went bad, it lost over 100 FPS.
It looked like this:
1581047372_19704860485e3cde4c8bc597.47199427_ccc3.jpg

 
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I'm not surprised that your accuracy is off. I've never tried the 16 at that low velocity, usually more in the 880 range. And even then, the 18 has always been better for me at 50 yards or beyond. With the big change in accuracy at 100, but good at 50, I'm guessing your previous velocity was about the minimum for good performance at 100 yards with that pellet. 
 
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ELH, yes I agree with you. I'm pretty sure the drop in velocity caused the accuracy issues at 100. I had purposely de-tuned the gun to shoot the 15.9s in that 850-855 range because that was the lowest velocity it would consistently group with out to 100 with the 15.9s.

What I'm trying to understand is what is causing the drop in velocity. I hadn't adjusted anything in well over a year and two weeks ago the same gun was shooting those same 15.9s right around an inch at 100 yards just as it had been for the last year and half.

Thx!

Tracy
 
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ELH, yes I agree with you. I'm pretty sure the drop in velocity caused the accuracy issues at 100. I had purposely de-tuned the gun to shoot the 15.9s in that 850-855 range because that was the lowest velocity it would consistently group with out to 100 with the 15.9s.

What I'm trying to understand is what is causing the drop in velocity. I hadn't adjusted anything in well over a year and two weeks ago the same gun was shooting those same 15.9s right around an inch at 100 yards just as it had been for the last year and half.

Thx!

Tracy
Click to expand...

Yes, that is odd. But as I have discovered, there are many oddities in the world of air rifles. Go with the flow....uh, so to speak.
 
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