How to set up your air rifle
From Shooting.Wiki EN
If you can move your pistol grip set it to zero position bevor you continue. The easiest way how to get the correct length of the rifle is to place the butt plate into the crook of the arm. Now change the length until the shooter can grab the grip properly. Now extend the length by 1-2cm (0.5-1").
The butt plate should not be inserted dirctly in the shoulder, but between the shouldern and the upper arm (above the upper arm muscles). As you extended the rifle length it will press strongly against the shoulder. Reduce the length bit by bit now until the butt plate fits tight but not unpleasant. In the best case the arm will not lie against body but hover some centimeters (1-2") automatically.
Lower the butt plate as far as possible, move it upwards 1-1,5cm (0.5") again and thighten the screws (basic position).
Set up the cheek pice
Move the rear sight to a distance of 5cm (2") between rear sight and aiming eye bevor you continue. One problem during the set up of the cheek piece is that the shooter immediately looks at the rear sight and begins to cheat head position etc. You need to prevent the shooter looking at the rear sight. Now the shooter should place the head onto to cheek piece with its complete weight. Make sure the head is not raised with strength. That way the neck is mostly releaxed. Tell your shooter to leave his head like it is bevor he can look at the rear sight again. The should should tell you if he can look through the rear sight properly. If not raise/lower the cheek pice or correct it sideward. After each modification you have to repeat the test.
If the shooter has to contract his neck he maybe needs a raised line of sight.
Fine adjustment of the butt plate
Untighten the screws of the butt plate and move it until the shooter aims a bit above the target center. Tighten the screws again.
Position of the rear sight
The distance between the aiming eye and the rear sight should be 3cm to 8cm (1.2" - 3.1"). Start with 5cm (2"), untighten rear sight (always keep one hand on it to avoid it from falling down) and move it back/forward until the shooter has a correct sight picture and can see the front sight sharply. Tighten he rear sight again.
Weight and balance
The maximum weight of an air rifle is 5,5kg (5500g, according to the ISSF rulebook). If you're shooting 3 positions don't forget that the weight of the hand stop counts to the total weight. There's no minimum weight.
Using weights in the near of the front sight helps to make the muzzle inert. The rifle should move slowly downwards at the front if the shooter puts the butt plate out of his shoulder. If not or if it moves fast you need to correct the balance and mount additional weights to the stock.