Determining Muzzle Velocity Without A Chronograph

[cobalt327]

When we were kids, we'd compare our BB guns by different ways. One was to shoot tin cans at point blank and see what the difference was. Another was to "race" out BB guns by shooting them straight up then measure the time it took for the BB to come back down. We figured the faster the MV was, the longer the BB took to make the round trip.

I just now measured a pair of new production Daisy BB guns, one a 'hopped up' Model 105 and the other a factory stock Red Ryder. The RR measures 8 seconds and the 105 is 9.5 seconds.

My math is weak and I found nothing I could use online. So my question is: Is there a formula I can use that will convert time up and back to MV? Or average speed, distance traveled, or ??

ETA Moderators, if this is in the wrong forum please feel free to move as you see fit. Thanks.

 

[readyeddy]

I know it's just bb's and pellets, but it's probably best not to shoot straight up.

If manufacturer's fps claims are not sufficient, then I would google search the question to see if anyone has chronoed the airgun, and if all else fails, you can always buy a chrono that you can also use for your powder burners.

 

[cobalt327]

One gun is modified, the other is stock and has a MV rating of "up to 350fps", but these Daisy BB guns generally do not make that MV. I cannot justify buying a chronograph for this, so if I cannot find a formula to put a number on it other time up and back, I'll bin the whole idea. But the thing is, there should be a formula.

No worries regarding shooting a BB straight up- where I'm at all it can hit is me or my property, both of which can withstand a 5.1 grain hit from a falling BB.

 

[readyeddy]

Google search came up with this video for measuring airsoft guns. Should work for bb guns.

https://www.youtube.com/watch?v=K-I_QRPTNuE

 

[cobalt327]

Very clever. I'll give it a try and see what I get. Thanks!

ETA Used a math formula, if it took exactly 9 seconds up and back the speed would be 295 fps, 8 seconds = 262 fps. Curious to see how close this is to the results I get from the sound editing software.

 

[jmorris]

What formula did you use, I am getting different numbers.

http://keisan.casio.com/exec/system/1224835316

 

[cobalt327]

http://ux1.eiu.edu/~cfadd/3050/Ch03LinearMotion/Hmwk.html

What are you getting? Using yours I'm seeing about 88 m/sec or 289fps for 9 seconds. Pretty close to what I got (295fps)... unless it's half of that. But going by what others have indicated seeing on a chronograph, it would seem that something between 250 and 300 fps is all that can be expected from a Daisy Red Ryder type BB gun. BTW, these numbers do not reflect air resistance.

 

[cobalt327]

The actual fps as shown by my chronograph turned out to be right at 275 fps.

 

[cobalt327]

In case anyone comes across this during a search, I'll add some info that will answer my original question:

A ballistic pendulum is what was often used before the advent of commonly available affordable chronographs. Old school but works very well.

Audacity "is a free, easy-to-use, multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems". It can be used for computing velocity, do a search online for details. I saw several YouTube vids on this and the setup is easy to do. Basically the audio program uses sound to measure the elapsed time of the projectile leaving the barrel until it hits a paper barrier set at a known distance. Velocity is computed using these parameters.

 

[Berger.Fan222]

In case anyone comes across this during a search, I'll add some info that will answer my original question:

A ballistic pendulum is what was often used before the advent of commonly available affordable chronographs. Old school but works very well.

Audacity is a free, easy-to-use, multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. It can be used for computing velocity, do a search online for details. I saw several YouTube vids on this and the setup is easy to do. Basically the audio program uses sound to measure the elapsed time of the projectile leaving the barrel until it hits a paper barrier set at a known distance. Velocity is computed using these parameters.

I've done the Audacity tecnique. It works very well. It seems to work best with a resonant metal target that makes a good noise when hit. You can also place the microphone equidistant from the air rifle and the target so as to not have to correct for the speed of sound. That approach makes the math easy: velocity is simply distance over time, where distance is the distance from the barrel to the target, and time is the time between the sound of the shot and the sound of hitting the target.

 

[cobalt327]

In case anyone comes across this during a search, I'll add some info that will answer my original question:

A ballistic pendulum is what was often used before the advent of commonly available affordable chronographs. Old school but works very well.

Audacity "is a free, easy-to-use, multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems". It can be used for computing velocity, do a search online for details. I saw several YouTube vids on this and the setup is easy to do. Basically the audio program uses sound to measure the elapsed time of the projectile leaving the barrel until it hits a paper barrier set at a known distance. Velocity is computed using these parameters.

Wanted to add "Poor Man's Chrony".

 

[cobalt327]

Another method is outlined HERE.