Indexing Barrel liners in FX Impact - FX Wildcat

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I am currently testing the “ barrel indexing” issue myself and have a question.

in case you have found the tightest group at a certain position of a barrel , this indicates that at that position the barrel harmonics are most favourable for precision right ? Now if I am going to change a few fps in projectile speed hence changing harmonics , would this mean that my previous findings on optimum barrel position are useless ?

thanks a lot for your thoughts and know how


 
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Indexing at 10 meters with my .22 Impact, 18.13 JSBs, 2 shots per position, looking for best position for elevation purposes. At that distance I didn't expect to see much difference in accuracy from one position to another. The blob at upper right outside the circle was my aiming point.
indexing.1612061858.jpg

 
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Ladwict, if indexing changes POI then your liner is not perfectly straight. No big deal, few are. It also means that shroud/O-rings/jam nut at muzzle end are not eliminating the curve in the liner, otherwise indexing would not change POI.

I would bet anything that the frequency and/or amplitude of the liner oscillation is different for different indexing positions, which is why some notice tighter groups at certain positions. That just means that for that projectile, at that velocity, at that index position, the projectile is leaving the muzzle on an antinode of the liner oscillation.

Anytime you change velocity, regardless of indexing, you are changing the amplitude and/or frequency of oscillation. But you are NOT changing the fact that the muzzle points in a certain direction when indexed in a certain position. Therefore I would expect you to get roughly the same POI, but with better or worse grouping.

Long way of saying that a change in velocity is a change in harmonics, indexed liner or not. I'll bet there is an optimum velocity for ANY index position, and when you index and find one position gives the best groups, that is true only for that velocity. That answer?
 
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With the liner in the pic above, I tried indexing at 30 yd and got much more variation in POI than 1.5", yet it gives me average 0.4" 5 shot groups at 70 yards, so no I don't think what you're seeing is too much. I do think that if you're indexing, and you happen to find a position which gives excellent groups, you have simply found another way of tuning the harmonics. The other way being adjusting velocity/hammer strike/valve travel for a given reg setting. Attached is a pic of a 700 mm Superior (not heavy) liner I recently received from a reputable dealer who has consistently given excellent service. It looks like an unstrung longbow, and you can't look straight down the bore. I never bothered to shoot with it, just exchanged it, but if I had tried it I bet the indexing would have been spectacular.



bent liner.1612103351.jpg

 
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Hahaa.... your floor is crooked !! No serious...I believe there a lot of things to say and do re harmonics and for sure there is precision to be gained when you dig into the issue. One more quesrion I have. Many tuners speak about 12 and 6 o’clock position tuning. Does this mean the group that shows most dominant vertical spread of individual pellets/ slugs or the group that impacts in a vertical plane from your poa ?


 
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I think they mean that as you go around the clock you will find one position with the highest POA and one with the lowest. Since there is a limit to the amount of elevation we can dial into our scopes, and since scopes are at their best near the center of their dial range rather than at the extremes, if you want to shoot long distances you index for highest POA so you don't need as many "up" clicks to hit at long range.
 
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