Indians For Guns

I owe it to Basu for getting me interested in this.

For those who are uninitiated "Audacity" is a free sound editor. The sound of an air rifle shooting and hitting a target at a known distance is recorded and the recording is opened using Audacity. This shows a graphic display of the sound wave. Usually the sound of rifle and sound from target appear as two separate triangular shapes (the triangles are lying on their sides with base vertical on the left side).

The image below is of a sound recording I made yesterday of an IHP 35 hitting a metal target at 10 meters as seen on Audacity.


The recording is a stereo recording and that is why you see two blue triangles on two lines one above the other. The triangle on the left represents the sound made by the rifle and I have marked its length (duration) with a fat red line. The triangle on the right represents the sound from the metal sheet target. I have marked that with a fat green line.

Note that both sounds start very suddenly - "BANG!" and then the vibrations continue for some time. The left/rifle sound probably starts with the sound of the trigger sear being released, continuing as the scraping sound of the spring and piston, ending with the sound of pellet leaving super-imposed on sound of piston hitting the end of the receiver, followed by vibrations sounds of spring, stock and barrel. Because of all these combined sounds, the left/rifle sound is not a good triangle. It is like a half-egg shape and only after a short time gap the sound begins to fade down towards zero.

The right target sound starts with pellet hitting target followed by the gradually fading vibration of the target. This is a single "Tannnn" sound that creates a nice triangle shape as it fades.

The problem is as follows. We must know exactly the point at which teh pellet leaves the barrel and the point at which the pellet hits the target. Pellt hitting target is easy - the exact point when the tagert sound starts is the time when pellet hits target. But when exactly did the pellet leave the muzzle?.

If you measure the tme from start of rifle sound to start of target sound you get a muzzle velocity of about 90 m/sec. but the actual measured velocity by Chrony when I fired this particular shot was about 150 m/sec. So you cannot take the start of rifle sound as the point of measurement. What I did was to calculate the pellet travel time using the Chrony measurement. The value is 0.67 sec. I then drew a fat magenta coloured line from the point where the target "tannn" sound starts - to some point in the middle of the rifle sound - and that magenta line represents 0.67 seconds. Now how the hell can anyone look at the rifle sound and say "This is the point where the pellet left the muzzle and this is the point where I wil start my time measurement"?

Here is my suggestion:

The left side/rifle sound remains at the same high volume for a short distance after it starts. Then it just begins to fade down towards zero. When you want measure muzzle velocity using Audacity, start measuring time from the point where the rifle sound volume starts coming down and measure up to the start of the target "tannn" sound. In fact the magenta line coincides with this suggesting that the "true secret" of measuring pellet travel time on Audacity lies in measuring from the point at which the rifle sound begins to fade in volume.

What do you think Basuda?

Hi Bennedose,
> Goodness gracious....you're turning us into acoustic engineers
> Very well researched & documented
> One small query though ..."what would be the % of error" as compared with a standard chrony?
> Now that you have one....a comparative study would be welcome for us to get educated
Briha

Lol thanks Briha.

I will do a "double blind" study shooting pellets of varying weights and see how well my hi-funda waveform theories work.

Dear benne,
Thanks for issuing a thread in my name.
As per my observation , the sound was captured in closed place so the graph in respect of trigger release , piston travel ,air blast and subsequent discharge of pellet from muzzle got mixed up.
So it is very difficult actually to understand as to when pellet really getting discharged.I had your previous sound samples and they were also very difficult to read.
On the other hand I have sound samples captured in Sansung galaxy where 1st highest peak is easily understandable.I would request Sathya to put up that screenshot so that we know when exactly pellet leaves the muzzle.
I am an enigma when I find 90 vs 150.
Thnks for your effort.

Basu

WOW!

I shot 5 different pellets of different weights at random order and recorded the sound and the Chrony readings. I used the sound signature using the guidelines I have posted abve to estimate the velocity from Audacity and I am amazed at the accuracy. I now wonder whether I am bluffing myself - I am so surprised.

Here are the readings I got. I did not note the brand/weight of pellets but all were shot from my IHP 35

Shot 1: Audacity: 97 m/sec Chrony: 98 m/sec
Shot 2: Audacity: 139 m/sec Chrony: 143 m/sec
Shot 3: Audacity: 126 m/sec Chrony: 129 m/sec
Shot 4: Audacity: 135 m/sec Chrony: 132 m/sec
Shot 5: Audacity: 101 m/sec Chrony: 110 m/sec

The readings are so close that I wonder whether this is pure chance like a monkey typing Shakespeare. I will have to try the same thing with other rifles. Also I must point out that I had previously "analysed" the sound signature of the IHP. It should be possible to get the same accurate results without any such prior analysis.

It appears to me that my friend Basu uses a different method from me and I think he has devised a method that does away with many of the inaccuracies that require correction in my method.

That is some research.thanks bennedose.
regards
drjk

Basu wrote:Dear benne,
Thanks for issuing a thread in my name.
As per my observation , the sound was captured in closed place so the graph in respect of trigger release , piston travel ,air blast and subsequent discharge of pellet from muzzle got mixed up.
So it is very difficult actually to understand as to when pellet really getting discharged.I had your previous sound samples and they were also very difficult to read.
On the other hand I have sound samples captured in Sansung galaxy where 1st highest peak is easily understandable.I would request Sathya to put up that screenshot so that we know when exactly pellet leaves the muzzle.
I am an enigma when I find 90 vs 150.
Thnks for your effort.

Basu

You are dead right - my sound sample has picked up every sound made by the rifle including yawning, waking up and brushing teeth. In fact I did not understand why you were using your different method until now. I want to use some of your sound recordings to see what results I get.

Hi Bennedose,
> Firstly 'hats off' to your dedication & patience in researching & experimenting the various methods of sound check & velocity recording
> Secondly I would like to use the word "Audacious" ....for audacity to stand up to a Chrony
> Am amazed at the closeness of your findings - using the 2 different methods!
> As time goes by it would be interesting to do an exhaustive study using:
1. One AR with different pellets
2. One brand pellet with different ARs

Briha

Dear benne ,
I am amazed to see the result of your post dt 18.3.15.
Just tell me that the data of audacity is average velocity or muzzle velocity.
Pl.try once my process at 10 yds and use my excel sheet to reach muzzle velocity and let us know the result.
I am sending you modified excel sheet to reach muzzle velocity with Fpe both for RH and FH.

Basu

Dear benne,
I will further burden you with another sound application..called " Softchrono" of Talonairgun.
If you have a laptop..same can also be further researched.

Basu

hello
Posting this on behalf of BASU sir.
screen shot of the projectile measurement in Audacity software.

and the details or comments of this will be followed below bu basu sir.

Regards

Dear sathya,
Thank you very much for helping me out.
Pl.refer to the pic.above.
Capturing and reading of the sound sample is very important to get exact velocity of ARs.
Distance should be 10 yds from muzzle end to target and the phone should be at middle only , 5 yds .It is always better to to keep the phone closer to pellet path.
The phone should be covered with cotton cloth or towel to help capturing exact sound.
Pl. see that my sound graph is very clear , free from any echo..and other sound vibrations.
I avoided capturing 1st spike because that spike is caused by the air blast in the action/chamber before pellet exit the muzzle.
The 2nd spike is the exact time when pellet leaves the barrel and so the spike is followed by more intense vibes then the earlier spike.
Dear benne,
When I put your audacity data , presuming that as an average velocity , in my excel sheet....I am amazed to see the result which is almost same as your authentic Chrony.
I wish to get comment from sathya , you and others , whether or not I am correct in my graph reading.

Basu

Hi Basu,
While I admire your persistent endeavor in recording the 'velocities' of ARs, I'm rather curious to know as to how these findings will help you to:

1. Tune the AR to shoot smoothly
2. Improve its accuracy
3. Choose the right pellet brand & weight most accepted by the AR
4. Arrive at the optimum energy delivered at various distances viz. 25 yds / 35 yds / 50 yds / 75 yds....

I am sure your response would go a long way in helping AR enthusiasts understand the importance of evaluating velocity!
Briha

Dear Briha,
The way I see it.....
Objective is simple..... to find out velocity to see at what stage it gives best power and also comfort.
Obviously not to shoot at 100 yds.

Basu

Basu wrote:Dear benne,
I will further burden you with another sound application..called " Softchrono" of Talonairgun.
If you have a laptop..same can also be further researched.

Basu

Basu I will try this out - and I saw your email. I regret I do not use Microsoft products as far as possible and so I do not use Excel.

But I am getting to be more and more confident that calculating Muzzle velocity using Audacity ia about as accurate as a Chrony. No need to invest in Chrony if you learn how to correct for errors in Audacity. (This true for air rifles. For regular firearms a few other issues crop up and a Chrony may be better)

But on the more general question of "Why measure velocity?" here are my thoughts.

Let me start with Precihole. In order to deliver the advertised 12 fpe (16.3 Joules) as mentioned in the Precihole website a Precipell 0.22 pellet, weighing in at 960 mg (15 grain) has to be shot out at a muzzle velocity of 180 m/sec (600 fps). My Orion has never delived 180 m/sec with heavy pellets like Precipell or GSmith. It does deliver 180 m/sec with lighter pellets (about 11 grain/ approx 700 plus mg). That means power never reaches the advertised her majesty's 12 fpe limit.

All other air rifles I have tried provide approximately the same amount of power (more or less) . The power delivered by Indian air rifles is far faar less than what is allowable by law using the Deal wood test. There is no 12 fpe limit in India. That is her majesty the qyoon of England's desire.

Why are manufacturers sticking to such low standards? I am certain we can have much more powerful rifles that can easily shoot targets at 50 plus meters. That would even encourage manufacturers to put on decent scope rails and improve scope use in India. For less than 25 meters scopes are unnecessary and Indian air rifles are barely usable beyond 25 meters. What for? Why are we trying to be fakirs or mendicants? Can we not read and understand laws? We train 400,000 engineers a year but no one seems to look at these elemetary no brainer things. Why?

By encouraging more and more people to actually take the trouble to test velocity we can stop having speculation and myths about what our air rifles do. Weights of pellet are known - and I have a database of pellet weights. We need a group of well informed and discerning users before manufacturers can be armtwisted to use their brains rather than sitting on their butts.