Spring upgrade??? Do you mean a standard G3/91 locking lever spring?
On my PDW (factory) I could depress the locking lever with my fingers. The one you made has an HK carrier with standard spring. (No-go with the fingers there). Remember me calling you during the summer about light primer strikes? I changed the PTR spring to a G3 lever spring that I CANNOT depress with my fingers and no more light primer strikes. Or are you talking rate of fire here?had some new spring made.. give me a call