I've been having a couple issues with my Krytac CRB. When it's on semi, it shoots normally at 390 fps at first but then randomly drops to about 200 and the bb basically falls out of the barrel. On full auto however, the problem disappears. Internally I've shimmed the gears, and installed a maddog Cylinder, cylinder head, and piston, a prowin hopup chamber, and a maddog M130 spring that I've cut down to shoot around 390 fps. I've had the same problem with other springs I've used in the past so the spring can't be the problem.
Here's a video of what exactly the problem looks like:
Any help is appreciated.