My G&G GR16 (M4) that I'm trying to revive from the dead is having firing issues. It will shoot maybe 2 or 3 times after I load a mag and will continue firing but no bb being fired. Also when it does shoot it's flying so slow I can see the whole flight path of the bb. It only goes out about 15-20 ft before it hits the ground. I believe the compression is good since I can feel the air blast more than a foot away from the nozzle. Hop up seems ok but the bucking was ripped so I replaced it but it's still shooting like crap. Went back and cleaned the piston head and made sure the holes were clear. Still the same thing. What am I missing here?