For each grain per pound draw decrease in arrow weight the penetration decreases by 9% while the effective range of a bow increases by one and a quarter yards.

For hunting I think that this means that one needs to use 9 grains per pound - the AMO standard - to be an ethical hunter. Only a fool would knowingly give up 9% in penetration for a 1.25 yard increase in effective range.

The numbers are based on "The Archery Program" where I looked at the momentum and KE at 30 yards - if the advantage of light arrows is long range shooting, then it does not make sense to look at closer distances.

At 30 yards, a 630 grain arrow has 35% more momentum and 26% more kinetic energy than does a 350 grain arrow. Momentum is more important for penetration, so each grain per pound of draw weight leads to almost a 9% increase in penetration.

At 30 yards, a 5 yard mis-estimation of distance leads to a 5 inch error with the heavy arrow. At 35 yards, a 5 yard mis-estimation of distance leads to a 5 inch error with the light arrow. A 5 inch error takes the arrow out of the "8 inch kill zone" so defines the effective range of the arrow. So for each grain per pound, there was a 1.25 yard increase in effective range.

The heavy arrow slows down less in flight because it is heavier and because the drag on it is less than on a faster moving arrow. The heavier arrow starts out with 10% more KE because the bow is more efficient at higher arrow weights.

Yes, yes, I know -> you already get full pass throughs on GOOD hits. Personally, I'm not good enough at this to assure myself that I will never have a bad hit. And I would suggest that one could use a blade with a greater cutting radius or more blades if one is concerned about leaving the extra energy of the heavier arrow in the bank on the far side of the deer.

And, the light arrow is much harder to tune for broadheads leading, in part, to the relative popularity of mechanicals. Light arrows being ironic in that they rob the arrow of down range KE plus encourage the use of a broadhead which requires MORE KE to make it function. All for a TINY increase in effective range.

Who is at fault? The bow manufacturers who have based their marketing on speed, speed, speed.

I want to also blame the archery magazines, but let me wait until I read a few more issues - I've been out of hunting for a few years, in the father business.

The above is based on a 70 pound bow, 30 inch draw, 31 inch arrow, 5 inch fletch, 7.5 inch brace height.

beprepn




Edited by - beprepn on 12/31/2002 16:16:31

Edited by - beprepn on 01/03/2003 18:46:56