I agree with Raineman. He is the man when it comes to bow strings. If you are having handshock issues maybe make some brace height adjustments as these older Bear bows sometimes like a higher brace height than other bows. Increasing arrow weight can help also. In looking into custom bows made today the one common thread I see quite a bit that the warranty is void if a FF string is used on a bow that isn't made for it. Maybe try the FF experimenting on another bow first to see the results. I have some old beater no-name bows laying around here that I try stuff I learn here first before I go to my Bear bows.

What Chad said.