Unscrew 2 trigger guard screws

http://i133.photobucket.com/albums/q...ff/BBS/012.jpg

Pull trigger back and turn stock anti clockwise from cylinder to unscrew

http://i133.photobucket.com/albums/q...ff/BBS/013.jpg

You can now access the mainspring

Unscrew bolt to remove cocking arm

http://i133.photobucket.com/albums/q...ff/BBS/014.jpg

remove cocking arm from cocking slot

http://i133.photobucket.com/albums/q...ff/BBS/015.jpg

You can now remove the piston assembly