Now that the absolute offence committed in inadvertantly possessing a 12.1 ft lb air rifle carries a mandatory sentence, the shooting bodies should be pursuing a standard test, probably based on a degreased pure lead ball fired through a cleaned and degreased bore and with ambient temperature within a specified range.
Campaigning for a change from using the word "weapon" in the legislation on the other hand is a waste of time and energy better devoted elsewhere IMO.
Adrian