how do you measure this? is there a calculation on how to do this? if there is what is it. I shoot carbon force radial x weaves 300pro and my bow is pulling 71lbs and some change. my draw lenght is 28 the arrows measure 27 1/4 from the insert to the bottom of the nock. my wifes bow is pulling 50lbs with a 26inch draw and shooting carbon force radial x weaves 200pro and her arrow measure 25 1/4 from the insert to the bottom of the nock.
GPI is normally used to determine arrow shaft weight. You can weigh the arrow and divide by the length or go to the mfgr site and they'll list it there. Once you have this and the other arrow component weights, you can figure out how much your arrow weighs.
Question, are you asking what is the weight of the shaft in grains per inch or how many grains in total weight should you be shooting at 71lbs? Because the weight of the shaft per inch should be on the arrow chart.
Grainsper lbs is 6grs so your arrows should weigh 426grs.
Gselkhunter