Most bows post their speed using a set group of parameters. My question is; is there any way one can extrapolate their actual speed (outside of the AMO/IBO srt parameters. For example, I shoot 60# with a 29 in. draw using 28.5 in arrows weighting 7.5 gr/in. Also a 100 gr head plus vanes and inserts and nock. How do I find my bow's actual speed? The bow is posted at 320 fps at 30 in. and 70#.

The biggest problem I see is calculating your total arrow weight. You are much better to actually get a true total arrow weight. I've found using average component values to arrive at the weight can have as much as 10% error. The IBO arrow is 350gr total weight you arrow is probably heavier.

Using a rough guess to make a rough guess isn't gonna be that accurate.

The following method can get you pretty close but it ignores diffences in spine and efficiency.

Take 320fps and square it 102,400
multiply it by 60 = 6,144,000
divide it by 70 = 87771.4
Take the square root of 87771.4 and you get 296.3fps

This means you loose about 24 fps by going to 60lbs.

You loose speed going to a shorter draw length (multiply the speed squared by 29/30 then take the square root)

And you loose shooting a heavier arrow (multiply the speed squared by 350/(your actual arrow weight) then take the square root).

You'll still may be off by about +/- 5% with this method or a lot more if the numbers you put in are not accurate to begin with.

Chronographs are not that expensive anymore dude!

Yeah, I know that chronos are not that expensive. But why spend $$$$$for a one time use???????????

Check with some of your hunting buddies that reload. Surely one of them has one they would let you shoot over. Just be careful a friend of mine put an arrow smack dab through the middle of one once.

alot of archery pro shops with a shooting range have chronys for the customers to use

Get yourself a Chrony, Since I hunt small game, predators and large game using different arrows, I learned what works best using a chrono.

A crony isn't for one time use. You can use it to tell things about your shooting. I use the one at the range and I can have a significant change of speed between shots just from a sloppy release (I shoot fingers though). When you get different arrows or make arrow changes with your existing set up it will tell you lots.

the chef

Hey guys, thanks for all your advice regarding a chrony. Unfortunately, all my hunting buddies are either dead or have moved far away! I did find a range with a chrony and after promising not to wreck it, (I am notoriously hard on ALL hunting equipment) I shot through and founs that my set-up shoots about 280FPS. Not bad!

ALL DEER BEWARE, I GIVE FAIR WARNING TO ALL!!!!!

I have a Short Draw at 28" and Have said that if I find a bow that would let me shoot at 280 fps or better I would buy it. I now shoot a BowTec is flys at 286 fps at 65 Lbs.

Okay: 280 fps. Did you weigh your arrows, too? I'm guessing they come in at 360 gr. Check your draw weight? Draw length? (They've probably got all that stuff if they have a chronograph.) Then you can do all sorts of arithmetic.