Originally Posted by Jamesy
Have you tried refitting the standard parts to see if it cocks with those fitted? That will at least eliminate the possibility that it's something else that's causing the problem and not the new parts. The HW requires you to cock/set the trigger unit before inserting it back into the gun, then you pull the trigger to release it before cocking the gun for the first time.. might be something you have/haven't done that's the problem and not the kit.
It works with the original internals in it, The old spring is a tad shorter than the new v mach one but only by one coil, so I'm genuinley out of ideas now.