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Thanks for your nice and clear posting. This tight goups at a certain barrel/ liner position occur because the barrel harmonics are most in favor of tight groups in that position of the barrel/liner. Now if you change your projectile speed with let’s say 15 fps due to slight change of settings ( regulator, hammerspring tension o.a) or different projectile (;pellet or slug) the balance of harmonics will change and your fine and perfect harmonic tune is ( partly) lost and you can go over the indexing process all over again isn’t it Chuck ?

for me this means that features like power wheels and other “ on the fly” adaptors for power are not very relevant as I tune my airgun for 1 pellet or slug at one reg setting and hammerspring balance and one barrel/liner indexing position. When I have all this right to my liking I will not diddle around on anynof these parameters as things will get out of whack more or less and to go over and over the by you described indexing process is rather time consuming and annoying. BUT I agree ...very usefull and obligatory for optimum grouping once you know what you want.
 
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Many opinions do exist bu for me aslong as they are nicely spaced and stay where I wanted them to be. ( block them in place with a few wraps of tape in order to not allow them to shift when pushing the liner in ). Exact placement is not very critical as long as you keep them where they are indexing your barrel. In my opinion a carbon or steel sleeve does only add to the equation of things that can influence the harmonics and no o-rings seem to me a bit “shaky” . Just my 2 cents .
 
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Ladwict: Thanks for bringing up a very good point I forgot to mention on this subject. When I index my barrel liner I am essentially "tuning" it to shoot one specific projectile! When you change something like the velocity your accuracy may change for the better or the worse. And just because my liner is indexed to its optimal position to shoot these Hybrid Slugs doesn't mean it will shoot pellets or other slugs accurately at all! 

So the bottom line is this...tune your barrel liner to shoot your projectile of choice at the velocity you desire for its best accuracy and leave it alone! This means you are going to have to decide which one you want to shoot accurately. Most air rifles will shoot several different kinds of pellets or slugs with some degree of accuracy, but there are no air rifles that will shoot everything accurately...so you must decide what you want to shoot and tune your liner to shoot it accurately and then stop fiddling with your gun. My .30 Impact is set on MAX and is tuned for shooting .30 Hybrids accurately - I have over three thousand of them to shoot up and then I will order more....at this point in time my rifle is a Hybrid Slug Shooter and I could care less about how it shoots pellets or anything else for that matter.

When you index your barrel liner try the whole process at different velocity settings to see what velocity and what position gives you the best accuracy possible...and once you find it go shoot a ton of pellets with it and have some FUN!



You are welcome Chuck. One minor alternative process I would like to point to as a small addition to your perfect explanation of your tune. In the last line of your posing you write “try the whole process at different velocity settings to see what velocity and what position gives you the best accuracy possible...”

My aproach would be to first determine at what speed you want to shoot your ammunition of choice. Secondly tune that speed on the knee ( I use to start with apporx. 15 fps below plateau) in order to be in the right ballpark for optimum efficiency of your tune. Third do your barrel indexing once you have found your desired speed at correct tune . Fourth play a bit with the hammerspring to fine tune best grouping speed in terms of a let’s say max. 12 fps range up and down as (only) slight speed variations do not seem to “destroy” your harmonics.


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Solo: I take the O-rings off the barrel liner and wrap tape around the liner at a few places to support it inside the barrel tube. I start by wrapping too much tape around it and then removing a little at a time until it just fits snugly in the barrel tube without having to force it. Then I unwind that first wrap and lay it out and measure it with a ruler and then cut three or four more pieces of tape the same length. So when I'm done the liner has four wraps of tape equidistant apart on the liner to support it.
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Top tip ! 
 
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Yeah, indexing FX barrels is always fun. I want to etch them to mark the position as the marker always rubs off. I'm one of those that pulls the liner to clean bc I find it easier that wrestling a patch worm through the breech. 

I'm going to mess with 3d printed liner spacers in TPU vs messing with orings. The orings always shift and drive me nuts. 

Any ideas on how to perm mark liners without harming them and I'm all ears! 
 
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at Home Depot I bought clear tubing that gos over the liner. It fits perfect but on some outer barrels are a little tight . then I lap with sand paper to smooth out imperfections and my liner is complete covers and tight no need for orings
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Nice idea indeed. I could imagine cutting a few pieces of silicon tube of an inch or so like Chuck suggested. Putting them in hot water. Sliding them to required spots . Let them cool down and see if they are fixed well as I expect them to be. Hope someone will try this and let us know. ( I do not want to touch my liner at the moment 😚)
 
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