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Chronographed, Real-World Bow Speed

Ideally, since your bow is transferring most all of its stored potential energy into kinetic energy of the arrow, your bow should generate roughly the same kinetic energy regardless of arrow weight within reason. The equation for kinetic energy is given below for both IBO and Real World (rw) arrow flight. Since grains (TAW) are a unit of mass, they can be substituted directly into the equation below.
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It is important to note that the number you get for KE using this equation and grains of arrow mass won't result in the normal KE measure of ft-lbs because the grains would need to be converted to slugs for that. If you want the actual KE in ft-lbs for any reason you'll need to multiply the result by the conversion factor 0.00000444 slugs/grain.

Anyway, back to my point, I use this equation to provide an estimated arrow speed for different weights of arrows in my current bow.
1713449588733.png
If the manufacturer's IBO claims are correct you should get similar results for the same bow setup as used in determining IBO speed. For instance, for my bow at 70#/30in draw and a 350gr arrow Elite claims an IBO of 332-335 ft/sec.

For my 540gr TAW from the same setup the calculation goes like this:
1713450505249.png
This is pretty close to the 270 ft/sec I've observed with my current setup.

1713450219389.png

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Bowtech sr350. Dead nuts on IBO. I'm shooting a 28" draw and 475 gr arrow, use an online arrow speed calculator, it's right where it should be. 286 fps with a 475 gr arrow, peep sight on string, 28 inch draw. 70 pound

One thing to keep in mind, all bows, especially these newer high preload short limb bows, the ATA measurement needs to be right. If it's big from string stretch you'll loose a bit of speed. My new sr350 was stretched to a 1/4" over ata and was 5 or so fps slow. I had to twist string and cables to bring it back to exactly at ATA spec and kept the timing/draw length correct. Now it's at the fpm it's supposed to be.
 
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