Well, The F4 is basically a pile of gearboxes and plastic. and the R72 is a Crosman that when you shoot, it's almost as if the Gearbox doesn't catch. It makes a revving sound and... doesn't shoot.
actually i dont need to fix the F4 because its beyond repair and i might just buy a new gun thats higher fps than my new gun but then again i might not even play airsoft any more or i might from time to time becuse i have to do other stuff like high school and sports and homework