Does anyone know the formula ???
Connecticut
I used to know a formula where you estmate FPS and shot your arrow using your 20 yard pin and 30 yard pin and I think you stood 30 yards away and aiming for the same 2 inch spot you measured how far your arrow dropped shooting your 20 yard pin and so many inces meant FPS ?? Does anyone ever recall a cheap test to estimate FPS. Someone I cant get a hold of anymore has my Chrono.
Calculate FPS of Your Arrows Without a Chronograph Steve Steve August 22, 2013 0 0
We recently posted a blog on how to calculate your bow and arrow’s kinetic energy output. If you know FPS, and your arrow total weight with a broadhead installed, it’s simple. But figuring out how fast your broadheads are launched from your bow often stops archers from completing the formula and knowing their kinetic energy. After all, not everyone has a Chronograph lying around. Below is a method to determine how fast your bow shoots with just a bow and a target.
By comparing the arrow drop at two distances, you can get a fairly accurate measurement of a bow’s speed in FPS.
1. Shoot a group of arrows from 20 yards using the pin you normally would. Concentrate on good form and pin placement. The more accurate you are, the more accurate your results will be.
2. With a marker or another arrow, mark the center of the group as reference point.
3. Back up to 40 yards and shoot another group of arrows. Use the Same pin you used from 20 yards.
4. Mark the center of the group. Measure the distance (in inches) between the two groups. Compare the distance to the chart below:
Distance FPS
28.7 220
24.2 240
20.6 260
17.7 280
15.5 300
13.6 320
12.8 330
Granted, this is not as accurate as a chronograph, but it’ll give you an idea of the speed your bow is shooting.
I just tried the formula out. I had a 17.5 " drop from 20 to 40 yrds so I guess im shooting around 280fps..im shooting a Mathews ld , 32" draw with a 523 gr arrow
There is a flaw with this method as arrow weight and fletching type will affect how much the arrow drops.. check out archeryreport.com they have a lot of info on kinetic energy, arrow drop etc
It sounds about right what most guys dont realize is a bows advertized speed is nothing compared to what it really does with your draw weight and arrow weight etc.I have a chrono and alwaqys used one. I have had so many guys say how fast there bow is and then didnt belive my chrono when they tried it and thier bow was 30 FPS slower then they thought. I basically did what you said but only went back 30 yards and only dropped about 6 inches. My Xbows advertized speed is 310 but that is with a 350 grain arrow and a fast flight string. I am shooting a 392 grain arrow but also have a expensive aftermarket string that says you gain 10 FPS. My scope compensates for yardage by matching a speed ring in FPS and I found that the 10 yard crosshairs were zeroed in out to 50 yards when the scope was set at 315 FPS and I would say this is close because when I set the scope speed ring at advertized 310 I was hitting high which meant actual speed was a little faster then 310.
