The Guy in the video figured out that you stock screw tightness can make an considerable difference to the accuracy of you rifle.
The chap in the video bellow experimented with a .22 rim-fire rifle, however, this could apply to Air Rifles as well, the tightness of you rifle stock mounting screws can make a big difference too accuracy, so give it a try, and see if this works for you just by loosing and tightening you rifle stock screws/fixings...

Unsure if the guy is trying to sell a toque screwdriver... maybe.
See video bellow and see what I mean...

https://www.youtube.com/watch?v=xAI0_LGnrak
If this works for you then this could be (ONE) of the problems between the same make of rifle shooting more accurate than another, something to think about... eh!
your thoughts please!