Might want to look at the 3 Rivers arrow spine calculator.
Its pretty good.
If you enter in the correct data.

30.5" GT 400s, w 100gr insert and 125 gr tip bare shaft fine out of my Blackwidow PSA2 at 46#.
Came out perfect on the calculator, once I fudged it by changing shaft length input by .5" since the brass 100gr insert is longer than the reg aluminum one.
Form factor was zero.

Not that I have great form, but am average size/build and consistent. Consistently bad or good or mediocre? LOL

I did have some 340s from my compound and I got them to fly decent, but the tip weight was a lot, and even when calculator and shooting proved them good, I found excessive frontal weight made the arrows slooooooooooooow, and not as forgiving of release.

My 400s fly faster, shoot great and are forgiving. Currently am running the regular Hunter series. Have shot the Pros before, in compound and recurve and like em. But for popping deer under 25 yards (no more 3 D shoots for anything other than fun)..........I just don't need to run the more expensive shafts.
Would go Hunter XT if a shop has em.

FWIW, will broadhead test each shaft, before hunting with it, in case one is outta whack.

Last edited by hookeye; 06/11/23.