estimating arrow speed

[nate c]

I chrony'd my Mohawk today:

125gr Tips swaged onto Cedar Arrows (520gr total weight) - 140/145 fps.
175gr Field tips screwed into GT 5575s (460gr total weight) - 165/170fps.

If I drop the 5575s down to 435gr, or bump them up to 485gr:  Can I conservatively expect to gain/lose 15 fps ~ for a 25 grain gain/loss difference in weight?

Thanks.

[zwickeyman]

It depends on your bow weight. You can figure 10 fps for the differance between 8 gpp and 9 gpp and 10 gpp etc.  Example, If your bow shoots 180 fps at 10 gpp it will shoot about 190 fps at 9 gpp. Hope that makes sense.

[nate c]

zwickeyman

Intuitively, that makes sense.  My two samples from yesterday (for a 55lb bow).  I lost 20 fps by increasing 1.09 gpp.  

145 fps @ 9.45 gpp
165 fps @ 8.36 gpp

The heavier arrow was Cedar, the lighter arrow was carbon with a more weight forward balance.  

They are both spined for the bow; I guess I didn't expect that much difference between materials.

Thanks.

[HATCHCHASER]

I have found that carbons of the same weight as wood or aluminum fly faster.  Don't know why.