Rangeball,
There is no "Rule of thumb" anymore for figuring weight/speed estimates......every bow is different and they will not all handle arrow weights similarly.
The only way to check for sure is to shoot different weights thru a chronograph.

You will also notice that a bows KE level doesn't change much from one weight arrow to the other.......
A bow only has one Efficiency level, and KE will only increase SLIGHTLY as arrow weight goes up.

This is real world stuff, and I'll illustrate it for you:

My BowTech "Pro38" Dual Cam is one of the fastest bows on the planet......I have a 30" draw length and am pulling 70# (IBO Specs)

At various arrow weights here's what I get:

350 grain arrow = 333fps = 86ft lbs of KE

370 grain arrow = 323fps = 87ft lbs. of KE

471 grain arrow = 290 fps = 88ft lbs of KE


Here's another illustration:
My Hoyt "Defiant XT2000" Redline 30" and also 70#
w/ same exact arrows.....

350 grain arrow = 308fps = 74ft lbs of KE

370 grain arrow = 299fps = 74ft lbs of KE

471 grain arrow = 268fps = 75ft lbs of KE

You can easily see that the efficiency of these particular bows does not change over different arrow weights.......this will be true of all bows.
If you are getting 74 ft lbs of KE with your set up don't expect much more than that with the heavier arrow.......especially with the shorter power stroke of that comes with a 28" draw length.

This also shows the difference in efficiency and how bows vary shooting different arrow weights........
With the Pro38 Dual Cam I lost 1fps for every 2 grs of arrow weight at the extreme light end of the arrow weight scale (from 350grs to 370grs)........and finally lost 1fps for every 2.35grs over the gap between 350grs and 471grs.

With the Hoyt "Defiant XT2000" Redline I lost 1fps for every 2.22grs at the extreme light end of the arrow weight scale (from 350grs to 370grs)......and finally lost 1fps for every 2.66 grs over the gap between 350grs and 471 grs.

Anyone care to analyze the efficiency between these 2 bows, with respect to arrow weight and the fact that one is a dual cam , and the other a hard single cam??


Anyway Rangeball.......I think you see my point. Making up numbers however logical they may seem doesn'y equal real world shooting and calculating.
Fire those different arrows thru a chrono and break out the calculator. I think you are in for a surprise. <img src=icon_smile_wink.gif border=0 align=middle>





Edited by - Matt / PA on 09/12/2002 21:34:03