well 517 with .36 is easily scratching if not above 600fps with .2's...
but it was not a hard pull. current pull with the 500fps on .2's is like butter. regular maintenance and super lube is all that goes into it. maybe you need to grow some muscles?
instead of preventing the selector switch from rotating to auto, it's much easier to mod the selector plate so that it never shoots full auto. basically, it's positions would be safe, semi, semi.