Got a nearly new BSA Mercury Mk IV .177 and it groups like 1" at 10 yards with RWS Superdomes. The breech bolt is tensioned correctly.
The trigger isn't great, but really this is springer pistol-level accuracy.

Before I do stuff to it, do you think it is

a. A dirty barrel.
b. A dislike of RWS Superdomes.
c. A scope issue.
d. A barrel crown issue.
e. Poor technique by me.