FX Impact Group POI Shifting

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RunningBull

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May 13, 2020
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I have a FX Impact MK II STX 600mm .22 cal w/PP. I have an issue that has been driving me crazy and that's a short drive. I'm experiencing good groups at 50yrds for about the first 10 shots, then the group shifts to the right about 1". I'll continue to shoot another 10 to 15 shoots and the group with shift again, sometimes back to the left or down. My first thought was the scope, MTC Optics Viper Pro Tactical 5x30x50 and the reticle was moving even though the turrets were locked for elevation and windage. I removed the MTC Viper and replaced with a Hawke Sport Optics Airmax 30 IR 4x16x50 and the shot groups are still shifting as with the MTC Viper Pro.

I've eliminated as much as I can from the shooter's part, stable bench using bench rest bags for front and rear, scope cant, hold, trigger control and follow through.

I have also noticed that if you change the Valve Flow Control settings the POI shifts. Could the VC be the cause?

I currently have my Impact tuned for JSB Jumbo Heavy diabolo at 18.13gr at around 930fps. I've noticed this happening with different fps, 890 to 950 and pellet weights, seems to be an issue no matter the tune.

Any thoughts? Has anyone else experienced the same issue?
 
I bought the rifle new back in March of 2020. It has been only recent that I've begin to verify it's potential. All of the groups are tight, say 1/2" to 3/4" at 50yrs but the shifting of the groups is my major complaint. I'm impress with its overall accuracy but not so with it's consistency, never knowing when the POI will change. I have an FX Chronograph to measure the muzzle velocity and the my SD is around 5ft per second. And before someone ask, I do remove the chronograph when testing for accuracy.
 
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I'm using the standard STX, not the new liners.
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The only thing that fixed mine was putting a Carbon Fiber sleeve on it. Mine had accuracy issues as well, but that came under control with a new regulator. But the POI shifting required the CF liner. Some in the know say that the “superior” barrel will also fix that. 
You will want to make sure that nut that holds everything together in front of the barrel has the right amount of tension, while facing Meca when Jupiter & Mars are aligned. 
 
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I have several FX rifles with STX system, and in my experience when POI change while you shoot, the reason is the barrel has lead fouling in it. A "cure" is to clean the barrel, and maybe lube the pellets. By that I mean you need to get all the fouling out. Take the barrel out if you like, and use a flashlight to inspect it. Usually you will see the fouling at the end of the barrel where the choke is. If the same behaviour comes back after relative few shots after you cleaned it, you need to clean again, and use some lube on the pellets. That will usually get rid of the POI issue. 
 
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I have several FX rifles with STX system, and in my experience when POI change while you shoot, the reason is the barrel has lead fouling in it. A "cure" is to clean the barrel, and maybe lube the pellets. By that I mean you need to get all the fouling out. Take the barrel out if you like, and use a flashlight to inspect it. Usually you will see the fouling at the end of the barrel where the choke is. If the same behaviour comes back after relative few shots after you cleaned it, you need to clean again, and use some lube on the pellets. That will usually get rid of the POI issue.
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X2. Had to get the bronze brush after one once to get all the lead out. No amount of pull through was going to cut it. 

Patches were coming out virtually clean. But two passes with a brush revealed lots of silver glitter still left behind. 

I polish with jb and lubed afterword. No more leading problems. 
 
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At Odolye. This is not my first rodeo. There is nothing wrong with my Hawke Airmax. I have used it competitively in 22lr BR matches and on high power NRA matches out to 600yrds. The MTC scope is new and was purchased to go onto the FX Impact. I might be somewhat new to the air rifle world but I do know my equipment from experience on other match quality equipment. But thanks for your input. 
 
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Wow. That sounds terrible bucketboy.
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When it’s zeroed, it was accurate but every single time I took it out, zero would have moved, I lost all confidence in the gun putting pellets where it was supposed to. Something zero would only be off buy 1 or 2 clicks, other times, zero would be off by 1” @25yards. None of my other guns ever suffer zero shift.



Bb
 
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