I found this a couple of years back and have used it for some of my classes. I wanted an opinion from the forum if you believethe formulasare accurate.

I know that chronographs have anerrormargin of + or - 2%.
I just don't want to distribute bad information........

***It seems that the table that I copied from wont paste correctly....please excuse the confusion.



Estimating Arrow Speed
Shoot a 5-arrow group at a spot on a LARGE target at 20 yards (use your 20 yard pin). Mark the center of the group with a pen/marker.
From 40 yards, shoot a 5-arrow group at the same spot USING YOUR 20 YARD PIN. Mark the center of the group with a pen/marker.
Measure the distance between both center marks and refer to the following table for an approximate arrow speed;







Approximate Arrow Speed (fps)
Distance between Groups (inches)





220


28.7



240


24.2



260


20.6



280


17.7



300


15.5



320


13.6



330


12.8



To calculate kinetic energy, weigh arrow in grains. Use approximate arrow speed and follow the following formula;
KE = mass of arrow X velocity (fps) X velocity (fps)/ 450240.

Example; a 400g arrow traveling at 270fps
400 x 270 x 270 = 29160000
2916000 divided by 450240 = 64.76 ft/lbs of KE.