How chronographs changed airgunning–and not always for the b
Posted: Sat Mar 02, 2013 5:42 pm
Great article. I never knew that one could get a machine to measure muzzle velocity.For many years I judged muzzle velocity by sound but could never get an accurate enough value.
After the advent of computers and video editing and sound editing software I discovered a hack/jugaad method of calibrating your air guns for muzzle velocity.
At first I tried doing a video of a pellet hitting a target at exactly 10 meters (measured). I used sound editing software to try and see exactly when the gun was shot and the sound of hitting a metal plate or tin can as time of reaching the target. Unfortunately I realized that the sound of an air rifle is never "bang" .It registers more like a "whoooosh" so you cannot exactly say when the pellet left the gun.
Last week I tried something different. I placed a metal sheet target and a balloon 10 meters away from the sheet. I turned on a sound recorder (cellphone) and then shot a pellet through the balloon to hit the metal target. This time it worked. I used a freeware program called "Audacity" to look at the sound recording of the balloon bursting and pellet hitting. You can use the software to measure the exact time interval in hundredths of seconds from the balloon burst sound to the sound of metal target being hit.
Once you have the time of travel for the pellet, you can calculate speed since you know the distance (10 meters in my case). the formula which any high school student will know is speed = distance/time
I used an old "local make" air rifle and got a velocity of 100 meters per sec (330 feet per sec) This is quite low - but I don't really care.
I have also tried using video editors to do this but they don't work. You really need a video camera that takes over 1000 frames per sec. The usual cameras do only 25 frames per sec and are not good enough