IBO question

T

tbird13

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Ok, so i have a thought, please bear with me.

I shot a bow today with an advertised IBO of 335. It shot 258 on the chrono.

From what I gather, advertised IBO is based on 5 grains per pound of draw weight. The draw weight on this bow is 60#. So the advertised IBO should be with a 300 grain arrow, right?

I only had the opportunity to shoot it with a 400 grain arrow. As mentioned, it chrono'd at 258 fps.

Simple mathematics tell me that 300 grains/400 grains=75%. So if I multiply 335 X 75%=251.25 fps. (I know this is probably oversimplified but NASA is on a temporary hiatus)

So that tells me that the bow is shooting relatively close (and better than) its advertised IBO.

I have not had the luxury of shooting many bows on a chrono-so my inexperience precedes me. My question...is this a respectable speed for that bow with this draw weight and arrow? and/or are my thought processes accurate? or is this bow just exceptionally slow?

(this bow was a 28"draw, i know that is different than what advertised IBO uses and has not been factored in)
 
IBO speed rating is always done at 70 lbs and 30" draw with a 350 grain arrow. A bow will lose 10 fps for every inch under 30". At 28" you will always have to deduct 20 fps from the bows IBO rating with a 350 grain arrow @ 70 lbs.
 
CT is correct with his statement of the IBO standards. A speed of 258fps out of that setup isn't bad at all. If you haven't gotten those modules changed yet, your speed will increase further once you do because you gain a longer power-stroke with a longer draw. Think of it this way.....(typically)the longer period of time the arrow is on the string, the more speed will be generated. If you haven't changed them yet, then I highly recommend you do that before you start building all kinds of bad habits and potential form issues that will cause you all kinds of problem down the road.
 
Thanks for the info. I am really happy with the way the bow shot and will likely make a purchase soon, just wanted to see if anyone had any input on the speed. As long as the speed seems in line with expectations and advertisements, I am happy.

Thanks again guys.
 
Your Correct....5 grain per pound. The advertised IBO is at 70lb, 30" draw with a 350gr. arrow. So yes...on 60lb. is a 300 grain.
 

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