That's unclear. I realize the scope's elevation and direction are adjustable, but there must be a separate kind of attachment that prevents the scope from coming off the barrel in the direction of the barrel.
There are two grooves that run along the top of the rifle.
The telescopic sights are initially aligned in these grooves and screwed tight in position.
A target is then set up at the relevant shooting distance.
The cross hairs in the sights are then aligned with the middle of the target and a shot is fired.
Depending on where the bullet hits the target, the sights are then adjusted up/down /left /right (using either a screwdriver or on more modern sights a dial) until the shot hits the target where the cross hairs are - zeroing!
The fiddly element to zeroing being a pointer as to why JB(?) removed the tele sights prior to the murders, as they are time consuming to re-zero, but would get in the way / not be necessary when shooting at close range.
