Illuminated Diablo 18" FOC

[ejb]

Hey guys
If i'm figuring this right the regular diablo 18" bolt w/150gr field point foc is 19.2. The illuminated diablo foc is 17.5. Can anyone tell me if this is right and if the 17.5 foc is ok or do I need to add some weight up front? Thanks

[Normous]

Don't sweat the petty things and don't pet the sweaty things
Your GTG at normal xbow ranges!
Past 50 or 60 y you may want to uniform FOC.

[nchunterkw]

As Norm said...GTG. As for it being "right".....here's how I measure FOC.

1) measure the arrow from the end of the nock to the end of the insert. This is Total Length (TL)
2) Divide that in half, measure that distance from the nock and mark the arrow. This is the Center Point (CP)
3) Find the point where the arrow balances. Mark the arrow. This is the Balance Point (BP)
4) Measure the distance from the center point to the balance point. This is FOC Length (FL)

FOC = FL divided by TL times 100

example:
Nock to insert 18 1/4" = TL
Half that = 9 1/8" = CP
Balance point 3 1/2" forward of the CP

FL = 3 1/2"
TL = 18 1/4"

FOC = (3.5/18.25)*100 = 19.178%