OHRedneck:

As I said; rocket science is not required to determine the setup necessary to do the job. Of course, you can formula the hell out of physics. However, what great advantage is realized?

Mike from Texas:

Even if you shoot a lighter arrow than necessary, as long as the total shaft weight is not less than recommended for a 70# draw-weight, you will have all of the necessary momentum required.

Keep in mind: light arrows often means more bow shock, more noise, harder on bow, and can be more sensitive to post-shot recovery than a heavier arrow.