Big and 3D,

I understand what you are saying, but from a practical standpoint just a little extra total arrow length can change the spine of your arrow. For example I had a set of arrows whose spine was supposed to plenty adequate for the poundage I was shooting. In fact I was about 8 pounds of drawweight below the charted spine limit of the arrows. When I added the same weight broadhead to the shafts(100grain)the arrows would not group with my field points at the same poundage. Backing off the draw weight 3 pounds allowed the broadheads to group with the fieldpoints. Take the broadhead back off the arrow, push the poundage backup and the arrow would group in the same spot, or leave the lower poundage add the fieldpoint the arrows would group with broadheads. The arrows were spin tested for being true. The only factor that changed was the arrows total length by adding the broadhead. The flex nodules of the arrow had changed with the slight difference in the length of the arrow.

Aim Hard!