FX FX Streamline barrel to reservoir gap

I have two .22 FX Streamlines, one walnut, the other composite stock. Otherwise they are set up the same, and have always been virtually indistinguishable in terms of groups.

I shoot, mainly CPHP 14.3 gr pellets @ ~1,000 fps, because we shoot to 160 meters under typically windy conditions, so the added velocity helps more than a bit tighter groups at lower velocity.

More recently, the composite stocked Streamline is not grouping as well as the walnut stocked one, and I'm chasing possible causes.

Velocity variations remain virtually the same for both, and for a couple of years.

The composite's barrel to reservoir tube gap is not uniform converging from 0.053" at the action end, down to 0.005" at the muzzle end.

Both had barrel bands, 3D printed, with significant gap around the barrel, neither one has the band very close to the barrel.

Both have plenums added, but since both have been virtually identical until recently, the fact that the walnut has a smaller plenum should be irrelevant.


Has anyone thoughts as to why the barrel gap is not parallel? The barrel is not bent, and the reservoir ends are fully seated with no gap.
 
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There's a lot of things to check for sanity:
  1. Is the air tube consistent in OD? (if it's not, this is a major concern. It's highly unlikely that this is the problem)
  2. If the shroud concentric to the barrel? (I'm more familiar with the dreamline, but it is possible that the two could be out of alignment)
  3. Is the shroud actually straight still? Is it possible that the barrel band induced strain into your rifle and caused the shroud to creep?
    1. You've suggested that the shroud/barrel are not bent, but how did you confirm this?