Where did this advice originate?

Hi all,
I am enjoying my Kempton airgun fair bought HW45, however as is often noted for these pistols she is a Smokey old bird. Whilst this backs up her almost unused appearance I would like to rid her of this filthy habit. I checked the online owners manual and found no recommendation from HW to dry fire twice to size the seal. So where does this advice originate? And if you have tried it please advise if it worked or made no difference to your HW45?
Cheers
Rich