I think when FF was new, the bowyers simply didn't know what might happen, so they didn't guarantee the bows against something that they weren't specifically designed to do. Which is a Good Business Decision, IMO.
I don't think using FF would void the warranty on my '90 Hunter, though it might've done so 25 or so years ago. ;)
This is one of those questions that makes me wonder how accurate Stu's calculator is on such things....
According to the calculator, switching from B-50 to a 14-strand FF would raise my spine requirement by about #2.5
So I plugged in the numbers for wood shafting (#55 Hunter drawn about 26.5", using 125-grain point, and 0.1" as my token strikeplate number).
With B-50, that bow (sez Stu) will throw a 27 3/4", #60-spine shaft (all up 504 gr) at 178.4 FPS
Switch to FF, and it'll throw a 28" #65-spine shaft (516 gr total) at 180.9.
Kinda makes you wonder if the calculator is off, because I'm not sure I see much up-side.... Going up #5 in spine rating sounds like a big win, but the heftier shaft comes with a slight weight penalty, so it's a matter of 2.5 feeps... And about 1.6 fpe. I guess you can look at that as a 5% boost in output, but from a glass-half-empty POV, it's just a dozen grains going less than 1.5% faster.
Guess I'm wondering what the fuss is?