Welcome to the sometimes frustrating world of airguns.
As to barrel variability - yes this can occur, but generally such variability is not to the extreme you are experiencing.
You mention you have tried cleaning the barrel - how thorough was the cleaning?
Sometimes lead deposits can be stubborn to shift.
You also mentioned at some point that the rifle has been stored in a case, is there a possibility that some moisture could have been trapped in the barrel that has caused a patch of corrosion in the bore?
One other thought, IIRC the HW100 has a two piece action block - is this still firmly bolted together as if the scope is on two piece mounts it could theoretically cause some movement if the two halves are loose.
People who have been there focus on the fundamentals. People who sit at keyboards all day focus on the trivial and inane.