Since a cocked spring resides partially within the piston and the exposed bit has a spring guide, I don't really see any advantage of pre-setting the main-spring.
Rustam
Hmm ... on 'the other forum' (Airgun Forum) there is an article on how to make a spring-setting device. Basically it is a long bolt inside a tube and a couple oif washers. The spring is compressed using this device until it is coil-bound, the tube preventing it from bending or forming a spooky s-shape while this happens. It is left in this pent-up state for a short time then released, and can then be placed in your pride and joy.
Apparently the spring is then 'set', and will perform better in your rifle.
Does anyone do this, and does it make any difference, or is it an American fad?
Since a cocked spring resides partially within the piston and the exposed bit has a spring guide, I don't really see any advantage of pre-setting the main-spring.
Rustam
Setting a spring just make it a bit easier to fit in the gun if you were doing it by hand
If you were to put an unset spring in then it would take a set after the first few shots anyway.