I changed the spring on my Airsporter ...managed to unscrew the trigger block easily but getting it back was a bit of a faff ....should have used a sash clamp . There is not that much spring compression but those threads on the end of the chamber are very verrrry sharp and blodied my fingers raw .
By comparison the later Rb2 type use three hex bolts - easy peasy , and takes less than 5 minutes to do a spring swop .