Home-Made Chronograph Guide!!!

[Mau]

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Home Made Chronograph Guide
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With this guide I will help you make a simple chronograph with items that you can find in most households. Based on how carefully you take your results you can yield very precise results. I won't say that this method is accurate(as I don't have a professional grade chronograph to compare it to), but the results are very consistant and can serve as a quick and easy way to compare your guns against each other or with different internal setups.
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YOU ALSO NEED
Download Audacity (Open Source sound recording utility)

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How it works:
The method of "clocking" your gun is based on the time it takes for a bb to travel from the moment you fire a shot, to the moment that the bb impacts an object at a known distance. Hence the term Feet Per Second. FPS.

1. Find an area with 5-15 feet of space near your computer to shoot.(guaging the speed closer than 10 feet is difficult - but yields an FPS close to the actual muzzle velocity)

2. Setup a solid target, or an object that will make a loud sound when the bb hits it. (Not your friend. We are looking for something like a popcan.)

3. With the measuring tape measure how far away you intend to shoot

4. Position the microphone to pick up both the sound of a shot being fired, and the bb hitting the target.

5. Load up Audacity

6. Cock your gun

7. Wait for silence(tell your friend to stop talking) and Hit the record button

8. From the measured distance - fire your gun.

9. Stop recording.

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Calculating the FPS:

All we are going to do at this point is to find the time between these 2 peaks, of these 2 sounds.

To do this all you need to do is select the space between the two waves with the mouse, and on the bottom it will show the time between the two waves.


FPS = Distance/Time

In this example, I used a distance of 22.5 feet and got a time of .085682 seconds

FPS = 22.5 feet /.085682 seconds = 262 FPS

That's it!
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Summary, Extra Notes
With this calculation we are merely calculating the average FPS over the distance we measured. Not the true muzzle velocity.

If you do this test, post your results!

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Tips:
*To get precise results, select only the sound of the shot and the initial hit (first 2 waves) and trim everything around it. You should also note that some microphones will pick up the sound of you pulling your trigger, don't mistake that for the sound of the shot. Zoom in and select the distance from the highest point from the shot, and ricochet to get consistent results.

*Place the microphone in the middle between the popcan and the firing position, this negates the speed of sound from the result.

*Also be aware of the position of your gun in relation to the distance you measured on the floor. If you are holding your gun 3 feet over the line, you will be skewing your results.

*If you want to get an approximate muzzle velocity(what they guage for competition) try the test from a closer distance(like 5 feet). If you want consistant easy results for comparing one gun/configuration to another, use a larger test range.
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My Results:
(From 22.5 Feet)

KWC Desert Eagle Spring (Ultra-Grade)
- 0.20g BB = 187 FPS
- 0.12g BB = 255 FPS (average)

Tokyo Marui Spring MP5-SD3 (old)
- 0.20g BB = 180 FPS
- 0.12g BB = 205 FPS

20$ Desert Eagle - unknown brand from airsplat 3 years ago.
-0.20g BB = 167 FPS
-0.12g BB = 190 FPS

The other noname springers from walmart clocked in around 140-175 FPS - note these were the ones that were claimed to shoot "290 FPS" on the box. Where in reality it was almost half what was advertised. Confirming the fact that they are in fact shit, but we knew that already

[Mau]

Whew! Finally done, that took a lot longer than I thought.

[MunkyMo]

The only problem with doing this is that airsoft rounds loose speed even over 10 feet. This is the reason most professional airsoft cronos measure right at the end of the barrel. That way it tells you the true mozzel volocity.

[Eclipzed]

Atleast its a rough estimate... Just to give you afeeling for what the other guy is going to be feeling on his end...

[Matt]

Thanks for going to the trouble of posting this.

Stickied.

[Nocte]

The only problem with doing this is that airsoft rounds loose speed even over 10 feet. This is the reason most professional airsoft cronos measure right at the end of the barrel. That way it tells you the true mozzel volocity.

You have a point, although this could be easily fixed by moving the can closer to the muzzle. I don't know why 20 feet was the range tested (I'm sure there is a reason), but, in theory, as long as you could make the results out from the piston slamming and the sound of the can getting hit you could move it as close as you wanted.

[DMitri]

It looks like you had the mic closer to the gun according to the waveform. If you moved it more in between the two, you could reduce the distance between the objects and maintain the ability to distinguish them easily.

Yes, thanks for taking the time to do this.

[Slyone]

This was on Hack A Day a while back, already have one setup. It's actually not a half bad way to estimate if you can't afford a chronograph.

[Mau]

It looks like you had the mic closer to the gun according to the waveform. If you moved it more in between the two, you could reduce the distance between the objects and maintain the ability to distinguish them easily.

Yes, thanks for taking the time to do this.

Good observation, for my measurements I placed the microphone equidistant between the popcan and the firing position, this negates the speed of sound from the result.

In the example the first waveform was a lot bigger because the sound of my gun firing was much louder than the sound of the BB hitting the target.

[MunkyMo]

The only problem with doing this is that airsoft rounds loose speed even over 10 feet. This is the reason most professional airsoft cronos measure right at the end of the barrel. That way it tells you the true mozzel volocity.

You have a point, although this could be easily fixed by moving the can closer to the muzzle. I don't know why 20 feet was the range tested (I'm sure there is a reason), but, in theory, as long as you could make the results out from the piston slamming and the sound of the can getting hit you could move it as close as you wanted.

Very good point Nocte. As long as you understand the math and reduce the range from 20 feet to lets say 5 feet you should get a more accurate muzzle velocity (Which is the FPS that matters).

The reason we use muzzle velocity to measure our AEGs is because it is the true AEG firing speed and we can use this to determine the impact Joules of a point blank shot. Now once the round has left the barrel the range/impact FPS/ and impact joule would be determined by the weight of the round as well as the FPS of the aeg (because heavier rounds carry farther and hold there momentum longer).

Try reducing the distance between the can and the barrels tip and see if the FPS changes any. This way we can determine how much the BB slows down in 20 feet.

[Mau]

The only problem with doing this is that airsoft rounds loose speed even over 10 feet. This is the reason most professional airsoft cronos measure right at the end of the barrel. That way it tells you the true mozzel volocity.

You have a point, although this could be easily fixed by moving the can closer to the muzzle. I don't know why 20 feet was the range tested (I'm sure there is a reason), but, in theory, as long as you could make the results out from the piston slamming and the sound of the can getting hit you could move it as close as you wanted.

Very good point Nocte. As long as you understand the math and reduce the range from 20 feet to lets say 5 feet you should get a more accurate muzzle velocity (Which is the FPS that matters).

The reason we use muzzle velocity to measure our AEGs is because it is the true AEG firing speed and we can use this to determine the impact Joules of a point blank shot. Now once the round has left the barrel the range/impact FPS/ and impact joule would be determined by the weight of the round as well as the FPS of the aeg (because heavier rounds carry farther and hold there momentum longer).

Try reducing the distance between the can and the barrels tip and see if the FPS changes any. This way we can determine how much the BB slows down in 20 feet.

Good idea, i'm gonna go get the tape measure out and try it @ 5 feet. I just did 1 foot, and it seemed to maximize the amplitude of the waveform, (or that which the mic can pick up), so there is no way to discern a difference between the shot and hit at this short a range.

I may have to play with the microphones placement so I can pick up the sound properly. BRB finding the tape measure.

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Also something to get your head stewing. I'd really like to make a guide/function that we could use to determine a BB's velocity at a given distance away from the barrel (because it obviously will slow down).

If someone who knew the "True" muzzle velocity of one of their guns, and did this test, we might be able to determine the muzzle velocity of our guns, by doing some math to our result from this test.

I believe its safe to assume that the resistance of air is the same for all of us. Ok I'm gonna go shoot something now.

[MunkyMo]

I will try to rig up one of these cronos at home this weekend. I will also use my real crono at mozzel then at 5-10-15-20 feet to see if I can get a graph of BB slow down (with .2's and .25g).

My G&P M16 shoots at the mozzel at 390 + or - 5 FPS so FPS varience shouldn't be to bad.

[Mau]

Ok so I tried it @ 5 feet, and my result has me leary, impressed, and very surprised.

The Manufacturer claims on the box the following statistics:
Power: 0.46 Joules
Muzzle Velocity (0.12g) = 290 FPS
Muzzle Velocity (0.20g) = 190 FPS
Muzzle Velocity (0.25g) = 175 FPS

My Result @ 5 Feet - 1 of each test only
KWC Desert Eagle Springer(Ultra-Grade)
5 Feet Avg. Velocity (0.12g) ~ 293 FPS
5 Feet Avg. Velocity (0.20g) ~ 219 FPS

So I went over to Arnie's FPS/Joule/Range Calculator and punched in their statistics to see how it would compare.

http://www.arniesairsoft.co.uk/?filnavn=/articles/fps_limits/fps_calc.htm

Assuming 0.46 Joules after plugging in the respect weights of the BB's here's what I got for calculated FPS:
Power: 0.46 Joules
Muzzle Velocity (0.12g) = 287.2 FPS
Muzzle Velocity (0.20g) = 222.46 FPS
Muzzle Velocity (0.25g) = 198.97 FPS

So their claimed FPS is under the theoretical FPS for the 0.2g and 0.25g BB's... Interesting...

Ok, before drawing conclusions, the results I just got from doing 1 test, while being very promising was conducted under very unique circumstances:
*I placed my microphone under a desk- next to the target, to prevent getting the full sound of my gun firing(it just overloads it with sound otherwise- and you can't see any distinctions in the wave forms).
*Unlike the tests from 20 feet, The 2 sound waves were overlapping on my test, because this was conducted from 5 feet away. The sound of the gun firing was still echoing in the room, while the sound of the object getting hit. So I had to manipulate the way I was viewing the waveform to distinguish the sound of the hit from the initial shot.(Zoom in and out a lot)
*The saving grace to all this inexact science, is that from the numbers I got came from the first selection range that I suspected from both wave forms.

As you can see below it is very hard to isolate the 2 distinctive waves since they are overlapping.



So from all this bibble babble we can conclude the following:
*The smaller the test distance, the more accurate the result will be to the true muzzle velocity. (the more difficult the test is too)
*You can effectively estimate the muzzle velocity of a gun by testing @ 5 feet.
*The Sound chronograph will give you the approximate FPS at half that test distance. So @ 22.5 feet we calculated 262 FPS for the example. That means about 11.25 feet away from the barrel the BB has slowed down to a velocity of 262 FPS. Thus the BB lost approximately 30 FPS over 11.25 feet .

[Mau]

I will try to rig up one of these cronos at home this weekend. I will also use my real crono at mozzel then at 5-10-15-20 feet to see if I can get a graph of BB slow down (with .2's and .25g).

My G&P M16 shoots at the mozzel at 390 + or - 5 FPS so FPS varience shouldn't be to bad.

The following data shows how quickly a BB will slow down over a given distance.

Data using KSC 0.20g bb’s.
Dist (ft) . Vel (fps) . Time (s) . Drop(in)
. .. 0 . . . . 320 . . . . 0.00 . . . . 0
. .. 5 . . . . 300 . . . . 0.02 . . . . 0
. . 10 . . . . 286 . . . . 0.03 . . . . 0
. . 15 . . . . 268 . . . . 0.05 . . . . 1
. . 20 . . . . 253 . . . . 0.07 . . . . 1
. . 25 . . . . 241 . . . . 0.09 . . . . 2
. . 30 . . . . 225 . . . . 0.11 . . . . 2
. . 35 . . . . 212 . . . . 0.14 . . . . 4
. . 40 . . . . 201 . . . . 0.16 . . . . 5
. . 45 . . . . 188 . . . . 0.19 . . . . 7
. . 50 . . . . 178 . . . . 0.21 . . . . 9
. . 55 . . . . 167 . . . . 0.24 . . . . 11
. . 60 . . . . 159 . . . . 0.27 . . . . 14
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. . 65 . . . . 150 . . . . 0.31 . . . . 18
. . 70 . . . . 142 . . . . 0.34 . . . . 23
. . 75 . . . . 134 . . . . 0.38 . . . . 28
. . 80 . . . . 126 . . . . 0.42 . . . . 34
. . 85 . . . . 119 . . . . 0.46 . . . . 41
. . 90 . . . . 112 . . . . 0.51 . . . . 49
. . 95 . . . . 106 . . . . 0.55 . . . . 59
. .100 . . . . 100 . . . . 0.60 . . . . 70

Data using Marushen Maxi 0.25g bb’s.
Dist (ft) . Vel (fps) . Time (s) . Drop(in)
. .. 0 . . . . 286 . . . . 0.00 . . . . 0
. .. 5 . . . . 273 . . . . 0.02 . . . . 0
. . 10 . . . . 261 . . . . 0.04 . . . . 0
. . 15 . . . . 249 . . . . 0.06 . . . . 1
. . 20 . . . . 237 . . . . 0.08 . . . . 1
. . 25 . . . . 226 . . . . 0.10 . . . . 2
. . 30 . . . . 216 . . . . 0.12 . . . . 3
. . 35 . . . . 206 . . . . 0.15 . . . . 4
. . 40 . . . . 197 . . . . 0.17 . . . . 6
. . 45 . . . . 189 . . . . 0.20 . . . . 7
. . 50 . . . . 177 . . . . 0.22 . . . . 10
. . 55 . . . . 172 . . . . 0.25 . . . . 12
. . 60 . . . . 164 . . . . 0.28 . . . . 15
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. . 65 . . . . 156 . . . . 0.31 . . . . 19
. . 70 . . . . 149 . . . . 0.35 . . . . 23
. . 75 . . . . 142 . . . . 0.38 . . . . 28
. . 80 . . . . 136 . . . . 0.42 . . . . 33
. . 85 . . . . 130 . . . . 0.45 . . . . 40
. . 90 . . . . 124 . . . . 0.49 . . . . 47
. . 95 . . . . 118 . . . . 0.53 . . . . 55
. .100 . . . . 113 . . . . 0.58 . . . . 64


Data referenced from: http://www.arniesairsoft.co.uk/forums/i ... opic=38192

This chart may help calculate your true muzzle velocity.

[Mau]

I took the same gun used in the other tests to Strikezone's game and chrono'd it in.

It clocked in as the following:
Muzzle Velocity (0.12g) = 295 FPS = 0.48 J
Muzzle Velocity (0.20g) = 220 FPS = 0.45 J

According to http://arniesairsoft.co.uk/?filnavn=/articles/fps_limits/fps_calc.htm the energy expelled was also calculated.

Which means a Sound Chronograph can tell you a muzzle velocity comparable to a real Chronograph, when properly analyzed at a range of 5 feet.