draw weight and speed

I know there are general rules of thumb about speed and IBO testing. For example, "for every inch of draw length you gain or lose 10 FPS" or "for every 3 grains of arrow weight you gain or lose 1 FPS". My question is what is the general rule of thumb or expected method for determining the draw weight and speed loss/gain? My PSE is currently set to 62lbs and I want to bump is up to 70. How many FPS would I gain by doing so?

Thank you.

 

You can't really determine an exact number. You'll have to shoot it and see. Of course arrow weight and spine make a big difference.

 

I know there's no way of knowing an exact number other than a chronograph; I am just looking for a rough estimate on how many FPS is gained or lost with draw weight adjustments. I remember reading something about 2FPS per pound of draw weight as a guideline....

 

Yeah, two feet per second is a very good guideline to use. That's usually an average amongst most all bows.

 

Here's a link to a calculator that should get you in the ballpark.

http://backcountrybowhunting.com/articles/calc/

 

Whoa man....thanks a million. Great link. I'm still learning when it comes to a lot of this stuff and links like that (or articles) are extremely helpful.

 

ya around 2fps sounds about right

 

No problem. There are a couple of others our there. Google is our friend lol.

 

Something to consider; those calculators work for the average set-up but if your arrow weight starts getting extreme I've found them to be way off. I found this when I was rigging up for water buffalo. The calculator was about 30 fps off when pluggin in my current numbers (580 grain arrow) and then trying to calculate a speed for the new 860 grain arrow. All I can figure is that the heavier arrow absorbs energy more efficiently so instead of coming out at the calculated 180 fps it chronographed at 215.

 

I'm shooting a 397 grain arrow at a 62" draw, not sure about my draw length, but I'll know pretty soon. I'm about to up my draw weight to 70".