If I use this formula:
Subtract 10 fpsfor every 1" you are under IBO length.
Subtract 1 fps for every three grains you are over IBO.
Subtract 2 fps for every pound you are from IBO.
Subtract5 fps for a peep site.
Subtract5 fps for a kisser button.
Subtract 4 fps for a string loop.

And I shoot at 65 pounds and have a 325grain arrow do I add 25fps for the arrow weight since I am under 350 grain? Or am I missing soemthing?
Thanks
Mike

65 lb @ 325 grain you would subtract 2 total (for every 10 grains +/- 3 fps is what I read...)

try this site

www.prairieshack.com

there is a speed estimator on the left.

Besides, adding 25 FPS would be way off (you're only 25 grains lighter), I know it's not what you meant, but thought I'd tell you, add 8 FPS for weight.

If you do a little math you'll find that rated IBO speed is at 30", 70# and 350 grain arrow (nothing on the string. Your figures above would be valid. However, if you divide 325 grins by 65# you come up with 5 gr/lb. Therefore no adjustment should be necessary for the difference in arrow weight/lbs determination.

Thanks that was the info I was looking for. It made sence to me that there would not be a loss if I was shooting 5 grs/per pound.
Thanks again
Mike

How much do you subtract for a pair of sims string leeches? Some people say they ADD speed! I can't get a straight answer on this anywhere. Thanks

Leeches generally put a little weight on the string. My chrono says that put approx. half way between the can and the center serving they reduce speed by 2-3 fps. If your end serving isn't too long you can run them closer to the cam (cams in my case). Moving them closer reduces the speed loss and can even make them act like speed balls, reducing some string oscillation and gaining a couple fps. It all depends on where they are located on the string. If it's for a hunting setup I always move them a little toward the center to get the best noise reduction/speed combo.