Just some clarification as to the UKAHFT rules !

In the rule that has been quoted, "if the gun goes off the shot is considered as having been taken & will be scored accordingly"

In this instance the gun "going off" refers to the gun actually discharging air, at the time of writing the rules we deemed "the gun going bang" to be less specific.

The gun "going off" would not apply to a Steyr where the cocking lever isn't closed & the sear just disengages upon pulling the trigger as air would not be discharged

Edit - Just for clarification.....it doesn't matter whether or not the pellet is still in the barrel as on some rifles if the bolt is left open the gun will fire air without dislodging the pellet. It's purely down to the gun discharging air