Some of my arrows with HIT inserts are supposed to be #10 too weak for my longbow but I have to add an additional 150 grs. of point weight to get them to fly correctly. Does Stu's calculator account for the fact that the back of the insert goes 2 ¼ in. into the shaft? The dynamic characteristics of the arrow would not begin at the end of the shaft but from the back of this insert. That would be like cutting 2 ¼ in. off your shaft. All my inputs into the calculator are correct.
Probably not so much the arrow spine as the bow design. An possibly the draw length.
Put the arrow in as you ended up and see the dynamic spine that your longbow needs.
Good info to have in the future.
Mike
never had any discrepancies using 100g inserts which are 1 1/2" vs 50g at 1".
Sure your + - center cut + plate is correct.
enter it as footed. length and weight. Don't enter a insert weight
Axis and MFX arrows act stiffer than normal shafts because the insert goes back farther and they are thinner putting the arrow closer to center shot.
I measured my center cut precisely to + 5/32 in. so in Stu's Calculator I entered 1/8 in. knowing the bow would be a little over a pound lighter. I think the problem is the MFX shafts. Thanks for the advice.
Found this old thread a bit late. I bought some 340's for a 50#28 bow based on estimates with Stu's calc. and tests with CE150's I use for my 43# bow. I trusted it since it was so good with my CE150's and have heard so many good reports. Turns out I would be better off with MFX 400's.
The calculator says a 32" MFX 340 with 75 grain insert and big 225 grain point for my bow are about 39# spine (which surprised me)... almost perfectly identical spine to a CE150 with 100 grain insert and 125 up front (which I already knew were too weak for my bow)
Yet in my backyard I can shoot each arrow at 30 yards. The 32" MFX with 225+75gr insert is what it took for me to get dead nuts for my bow and the CE150 is 3-4 feet to the right (very weak as I would have otherwise expected without the calculator).
If I enter the insert on the MFX as a 75grain footing and no insert weight (as suggested above)... I come out over 50# spine which is basically exactly what it says I should have. This knowledge would have been useful!
Since the MFX only have one insert option, I would suggest this calcuator be improved for these arrows, as it clearly is falling apart on the effect of the HIT inserts.
For now I guess I'll have to learn to love my giant lodgepole arrows and big FOC :archer: .