This morning I got up early but the wind was me one ahead and already moved some light branches in the trees and the flags was blowing varying from the 12 to 2 o'clock position, so a offset head wind. But shoot I will shoot. Yesterday afternoon it was 28 deg. Celsius and this morning it is 21 deg. and the air is much denser. On 50 meter I did 3 shots, right on the cross and about 12mm group. Holding the same dial as yesterday on the 100 meter dong, the shots fell a bit lower but it still grouped well in about 20mm main cluster and 30mm with the 1 outlier. So, I think the result is repeatable considering that there was wind this morning.
So, my expensive high tech modification was a piece of leather and tape. Because the barrel band does not fit snug around the barrel shroud with more pressure to the top side, I think there was from shot to shot differing vibrations effecting the POI. I then took a piece of leather and squeezed it in-between the barrel shroud and the air tube. At first I wrapped electrical tape around the shroud and tube but it had some side to side movement if pressed. I then add some duct tape (yes camo because that is what the shop had, I wanted black) to stiffen it and now I must twist hard before it move. And that is it. Nothing special and a bit unsightly but it works. It stopped that vibration that was different with each shot to happen. Next I will have somebody to 3-d print me a wide snug fitting barrel band I can put in place of the leather and tape and see what it is doing. Many rifles benefit from extra barrel bands, I read that as much as 3 bands get installed to dampen the vibrations. So, mr. Long_Gun_Dallas was right with his assumption.
I did a few other things to the rifle before this as well. Raising the action out of the stock with some spacers over the bolts so the action is riding on that spacers only. Now the wood moving with temperature and humidity does not put pressure on the actions and barrel. Like free-flouting a PB rifle. I also put a few O-rings over the barrel at 100mm spacing before sliding the shroud over the barrel. I also installed a bigger aftermarket plenum, polished the barrel, polished and lighten the trigger. Did a lot of pellet testing to see which shoots best. Sorting the pellets by head size. It was very obvious pellets with bigger head size was more likely to be flyers. Smaller head size did not have a problem. The H&N I have is mostly 5.52mm where the JSB I have is mainly 5.54mm and the reason my rifle does not shoot the JSB well.
In this picture you can see the piece of leather between the barrel and tube, sticking out just in front of the electrical tape.
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