ORIGINAL: zak123
I use this formula:
Subtract 10 fpsfor every 1" you are under IBO length.
Subtract 1 fps for every three grains you are over IBO.
Subtract 2 fps for every pound you are from IBO.
Subtract5 fps for a peep site.
Subtract5 fps for a kisser button.
Subtract 4 fps for a string loop.
I used this formula and was off by 1 fps.
I think about the only thing I would change/ add is that if you shoot a peep with a tube the figure is closer to 8-10fps loss.
Brass nockset--- 4fps loss each.