Crossover is where the scope is not in line with the barrel.
The result can be mild or severe.
Basically at near targets the pelletes strikes one side of the centreline, and far targets it will strike the other.

Not quite sure why I have developed this as a couple of weeks ago I thought it was spot on!!!

Could be scope shift, as the HW77k has a bit of a kick.....

Any thoughts on what I can screw down through the scope mount into the hole in the top tube of the HW? The holes are there but I don't have any bolts.....

Pete