Reply To: FX Impact: The Wait and Anticipation
Regarding the POI shift with moving shroud; first, barrels (on any rifle), rarely have bores that are concentric with the OD, and since the shroud centers on the OD, the pellet is usually going to travel closer to one side of the shroud than the other. Even if it doesn’t hit the baffles, the air compression in front of the pellet, as it passes the baffles is going to be higher on one side than the other. the pellet doesn’t actually have to touch to be deflected. just getting close on one side will do it. Second, Shroud tubes are supported only at the ends, or on the Impact, one end and near the middle when extended. in either case if the tube is not perfectly straight, it can cause pellet deflection, for the same reason. finally, barrels are rarely straight, even after being straightened on the outer diameter as close as the manufacturer is willing to do it, the bore may be aiming at a different spot than the outer diameter would indicate. So, now you have 3 sources of error in one barrel/shroud combo that could compound or cancel each other to varying degrees. add to that a shroud that could be slightly bent with one of the supports near mid length when extended, and the open end could be easily off center from the bore centerline. Even one-off custom guns that are built with tollerances as close as humanly possible are not perfect, let alone mass produced assemblies. So, I am not surprised in the least that some of these guns will have issues with POI changes when moving the shroud fore and aft. As a gun manufacturer myself,(not air guns), and knowing industry practices, I can just about guarantee that the first dozen or so prototype guns FX put out there, had much more time and effort spent on minimizing these inconcentricities than the guns that went out in the production runs. Short of checking everything yourself with a good lathe and dial indicators, your best bet is returning the barrel assembly for a replacement and hope for better luck the second time.
I do like the idea of a telescoping shroud myself, for the convenience of the shorter package when necessary; carrying/handling in confined places, like between boulders, heavy brush, or inside my car, when shooting out the side window; it also makes for a shorter carry-case. The sliding shroud is one of the reasons that I ordered an Impact. The system does seem to work for many owners, so I think your issue is probably just one of quality control.