Know Speed, No Chronograph ?

[JT of PA]

Is it possible to get a basic idea of the speed my arrows are going?

-- Ibex ... 175 lb. limbs
-- Excel String
-- 420 grain arrow

If so, how do you do it; is there a formula ?

Thank You.

[taz3]

My Phoenix was shooting about 290 fps until I put the Flemish string on, now it shoots 301 fps. They are the same, other then the thumb hole stock, so I would think you're around the same, anywhere from 280-290fps. I was using factory fletched Firebolts and 150 grain fp.
I do think there is a calculation to know the approximate fps, someone maybe able to chime in with it.

[CBRon]

Did you get a manual with your bow ? In mine on about the 3rd page there is a chart , It's very close to the speed of my bows.................Ron

[Cossack]

Based on chroning the Phoenix, I'm thinking about 280 with Excel string and 290 with Flemish. No formula exists per se as factors affecting speed include arrow weight, bowstring weight, brace height and perhaps even other factors like air density, etc.

[BigBadJohn]

Unless I'm wildly mistaken, the formula would be:

(arrow speed (fps) x arrow speed (fps) x arrow weight (grains)) / 450240 (ballistic constant)

Using the formula for a 175 lb draw weight IBEX launching a 350 grain arrow at 305 fps with the optional flemish string, kinetic energy calculates to be 72.31 ft/lbs.

Using the maximum potential of 72.31 ft/lbs from the above calculation, you can algebraically rearrange the formula to solve for the heavier arrow weight of 420 grains. It comes out to 278.42 fps. Hope this helps. It should be relatively close. BBJ

[awshucks]

You can come real close by working backwards from the advertised fps. Figure 8-12 fps for an Excel string vs FFF and 1 fps for every 5 gr weight change.

In your case, start w/ 305 fps - 10 fps for Excel= 295fps, 420 gr-350 gr= 70/5=14fps. 295-14=281 fps.

Not perfect, but dang close.........

[JT of PA]

Everyone ... Thanks for sharing your knowledge ... Now I know how to figure it out on my own. I appreciate the help.