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Discussion Starter · #1 ·
The specs on my Mathews Jewel bow says IBO is up to 325 FPS with #60 bow @ 29 inches. My Jewel is set to approx. #56 and my draw is 26 inches. Is there a way to calculate approx. IBO with these details without a chrono?

Also, the specs on my APA Sidewinder says the IBO is up to 318, but I can’t seem to find out if it’s also for #60 bow @ 29 inches… I seem to recall the #60 @ 29” standard/benchmark, is this standard?

Without that info, again is there a way to roughly calculate approx. IBO with the APA bow set to #58 with a 26 draw?

Is there a website that you can punch in your specs and it can generate what your IBO would be?
 

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IBO is normally 70lbs and 30" of draw with a 350 grain arrow [usually with no fletchings] and nothing on the string, but some MFGs will give different specs when a design doesn't meet 70# or 30", while others will "calculate" the speed from what the specs the bow is capable of.

Only way to know for sure is to chrono, preferably on more than one chrono.
 

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Just use the online calc, the IBo is for 70/30, so change all the info for what your bownajd arrow weight is. My last 2 bows have ended up about 5fps shy of what the calc says. Might be due to the chrono I had access to, either way it’s close enough


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Discussion Starter · #6 ·
Thanks everyone for the responses. I'll check out the site right now and I believe "TheBlindArcher" is right. I seem to recall hearing someone in our club talk about the #70 @ 30" with 350 with bare arrow and nothing on the strings. I also believe I can remember seeing something similar for my APA, just can't find anything online about it anymore, might consider calling APA out in Saska, Canada to get their take on how they did their 318 for the Sidewinder He1. Thanks man. :)
 

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Speed adjustment rules of thumb;
2 fps / 1 # of draw weight
10 fps / 1” of draw length
1 fps / 3 grains of arrow weight
1 fps / 3 grains of weight on the string
 

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Here's another way to get a general idea of arrow speed:

- Shoot a group at 20yds, mark the center of the group.
- Shoot a group at 40yds using your 20yds pin.
- Measure the vertical distance between the 2 groups

Your approximate arrow speed is as follows:

19.5inch - 190Fps
15.8inch - 210Fps
13.2inch - 230Fps
11.1inch - 250Fps
9.5 inch - 270Fps
8.3 inch - 290Fps
7.2 inch - 310Fps
6.4 inch - 330Fps

This is an approximation, but it should put you in the right ball park
 

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Discussion Starter · #9 ·
Interesting formulas, I've never heard of this technique, any online references fgignac? I believe you, I'm interested in knowing who put this together. :)
 

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Interesting formulas, I've never heard of this technique, any online references fgignac? I believe you, I'm interested in knowing who put this together. :)
I pulled it from Bill Winke's book Setting Up the Perfect Hunting Bow

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Discussion Starter · #12 ·
I’ve heard about that book, a colleague in my archery club mentioned it to us a few years back. Might see if it exists as an e-book for my phone and get a copy. :) Thx


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Amo speed was done at 60# 29" and a 540gr arrow. Ibo is at 70/30 with 350gr arrow. The jewel was done at 60/29 because it wasn't offered in a 70/30. So 325fps was found with a 300gr arrow.5grs per lb, because that's the minimum you can shoot without voiding most warranties. usually you lose 1fps for every 3grs over and its about 10 fps +/- for every inch of draw length. It can be ball parked to within 5fps. Here is a website that can help a bit. http://archerycalculator.com/estimate-bow-speed/

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Wal-Mart has the Caldwell chrono for $79.

Mine has worked flawlessly for rifle, archery, and air guns.

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Might see if it exists as an e-book for my phone and get a copy.
I bought it when I was just starting out and it served me well. Lots of good info for a beginner but probably wouldn't be overly helpful to an experienced archer. Still an interesting read though.

The pictures are a little dated (the book came out in 2009) but the principles or archery haven't changed since then so the info is still valid

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Here's another way to get a general idea of arrow speed:

- Shoot a group at 20yds, mark the center of the group.
- Shoot a group at 40yds using your 20yds pin.
- Measure the vertical distance between the 2 groups

Your approximate arrow speed is as follows:

19.5inch - 190Fps
15.8inch - 210Fps
13.2inch - 230Fps
11.1inch - 250Fps
9.5 inch - 270Fps
8.3 inch - 290Fps
7.2 inch - 310Fps
6.4 inch - 330Fps

This is an approximation, but it should put you in the right ball park
I like this charting, but these measurements and speeds would have to be for a specific arrow weight... correct? The chart would vary with varied arrow weight. I would be interested to see a chart like this that adjusts with variable arrow weight input.
 
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