Calculate Your FPS in Easy and Effective Way

[essdee1972]

Briha sir & Mercury sir, the calculation assumes constant velocity over the test range. Hence 605 would be the average velocity (assuming constant deceleration). The muzzle velocity would, therefore, be slightly higher. Of course, there are too many variables to effectively calculate the deceleration. And it may or may not be constant depending on the ambience (e.g. if you are indoors and there's a fan halfway down the "range".....). Now, as Avisek says, the impact will not be significant.

Avisek, thanks a lot! As for the deceleration, how do you calculate it? Apart from gravity, all other forces (wind, humidity, etc.) can be variable during the passage of the shot.

All the best for your new calculator!

Just a couple of suggestions. One, please please guard yourself and surroundings (both living and non-living things) from ricochets from the metal object. I once had an accidental case, when a flathead from my old SDB hit the plywood backing of the pellet trap, and ricocheted back 6 yards to hit me (not hard enough to hurt, but I could feel it hit). Two, maybe anchoring the gun with a vise or something might help to maintain the S, A, B distances.

[harshvardhan]

Thanks essdee1972,
I am Considering only the pellet weight and Gravitation-g
Wind And Humidity is ignored as every day these will vary and requires Complex Calculation.
This is a cost free approach using Mobile Phone,So I think its OK,
Please suggest me the ways for developing more accurate things.
For Target you can use Coconut fibers on the back of metal,For Cushioning,Its Great i Have tested it..

Regards,

[essdee1972]

Hey Avisek, I have absolutely no idea on how to improve accuracy!

However, I think the shape of the pellet will also be important, as the air resistance for a flathead will be much more than for a pointy, for example. The basic projectile theory I remember talks of "point mass", which, like the ideal gas, doesn't exist in reality. Point masses anyway don't lose velocity.

Probably if you have a friend who is an aeronautical engineer, or someone working in ISRO, NASA, DRDO, or any gun maker might know something about the resistance thing.

Anyway, your idea is quite brilliant. Better get some documentation ready, so that some big corporation doesn't plagiarise you! (and no, I am not joking here).

[harshvardhan]

Thanks ,
I am A mechanical engineer,And I can Develop procedure for making It More Accurate Procedure,
But Its is for all air-gun enthusiastic of IFG,
I do nod need recognition i need the smile in the faces....

Regards

[mercury]

fps will vary with weight and shape of pellet...definately...but lets take that out of the equation.

can we minimise the other factors in play...pointed out by Briha and essdee....by reducing the distance from muzzle to reference point??

if i were to reduce the distance the distance from 30 ft to say 5 ft...aware of the risk factor...would that not give me a better reading of the muzzle velocity ???

[mercury]

harshvardhan..... an edit...

by minimising" other factors ", i do not refer to humidity or the elevation we are shooying at.....

[harshvardhan]

Wait I am Calculating Factors and post soon

[airgun_novice]

Dear harshvardhan,

Fantastic concept. Congratulations for the innovative approach and the initiative.

Now likelihood of a few errors creeping in can not be ignored. Unless of course the 'listener' is tremendously accurate in terms of sensitivity and signal fidelity. In modern AP targets such "thuds" are measured and then calculations take place to determine the landing position of the shots. Ironically that's how they come up with 10.9 or 10.3 or such fantastic results. In fact, at one particular event, Abhinav Bindra objected to what was getting displayed as erroneous and that objection was upheld. So confident was he of his shot.

Another factor to consider in terms of improving upon the accuracy is the set of harmonics that might be generated both in closed and open space environs. Sound energy transmission wave being a longitudinal wave the "Universe" (System Set Variables) will play a significant factor in the final outcome. Successive interference patterns will set up beginning with the shot, the discharge (air/ CO2 in case of PCP or the thwack of the springer), then the flight (albeit, these ones will be weaker compared to others, unless one uses the supersonic (>=1000 ft/s) 'cracking' rifles and high speed pellets) and finally the impact. A dull thud viv-a-vis the one on metal bell ought to be preferred since the "clang" will set up over-lapping harmonics that will take a longer time to settle than the thud which will create a crest of significant amplitude and then dampen out quickly; thus paving way to set the requisite thresholds/ cut-offs using that acoustic software. You would ideally need to use an Op-Amp negative feedback circuit to improve zeroing upon the signal thus trapped even further. The filter would also need to take care of peripheral noise - both audible and electric. Unless these and other factors are rigidly studied, addressed, eliminated or co-opted accuracy will suffer. Thus what might be shown up as 550 fps may be anything like 500 <= true_value <=600 for example.

Hope you do give my 2 cents worth of thought some extra thought and evaluate the scenarios. I only wish I could be more involved and be of more value addition, but unfortunately it's been ages since I even held a soldering iron. Good Luck to you.

[harshvardhan]

Thanks,
A valuable Guide for me,
I want to Involve less Circuitry and Low Cost Version for each one and every one,
So that every one have a semi accurate low cost[even costless] chronograph handy with them,
I will keep your points in my mind to utilize these..
Share your vast knowledge with me for doing such work

Many Many Thanks

[Basu]

Dear Harsh,
I have tried your process at home and I found it handy enough to be used for
sport shooter but not for target shooter.
Here , how have I done it .
1) Downloaded Audacity software from internet.
2) Downloaded AVS Audio Converter-crack.
3) Downloaded your excel sheet.
Fixed a quiet place at terrace .Calculated a distance of 30 ft by measuring overseer tape.
Put 600 ml Pepsi/Coke pet bottle as target(it makes very clear sound).Put the android cell
phone at 15 ft away from gun end.So that the distance between gun to phone is equal to
the distance between phone to target.I kept the micro phone facing gun.Then putting the
phone in recording mode, fired 6 shots.
Transfered the sound data in computer.Using AVS Audio Converter , made sound in MP3
then importing the same in Audacity Software,zooming in the tall lines ,calculated the time
consumed between firing and hitting sound .Put the same data in your excel sheet and got
the FPS.
This FPS is the average time consumed by the projectile to cover 30 ft but not at muzzle.
In order to get the velocity at muzzle , velocity is divided by constant of 0.965.
With that effort my National 25 in 0.177 calibre delivered :
Gmith Competition -510 FPS at muzzle
Mastershot Wadcutter - 524 Fps at muzzle
My Local 35 in 0.177 delivered
Mastershot Wadcutter - 715 FPS at muzzle

Note : 1)While recording the sound phone should be wrapped with soft cloths all over.

2) This software cannot capture time, less than milisecond.

3) There should not be any fault in calculating the distances

4) The phone should be as close as flight path of the pellet.

Lastly it is a poormans crono , with no cost involved whatsoever.Since it is incapable to calculate
less that milisecond, so it can not serve the purpose of a target shooter.

I would request fellow IFGians , who has an authentic cronograph , to calibrate this and let us know
the difference ,if any.
I am very happy that instead of waiting to be cronoed, I can do it so easily.
Thanks to Harsh, thanks indeed.

Basu

[brihacharan]

Hi Basu,
> That's quite a remarkable & innovative way of determining the 'Velocity Capability' of an air rifle
> This method as we all know is subject to a lot of variables - however with an error of 5% to 8% it can provide a 'ball park' figure to satisfy one's curiosity & obsession with velocity
> Having said this, the 'weight & shape of the pellet too has a lot of influence / contribution in determining the velocity.
> On a weighted average 14gr pellets provide more realistic readings.
> It would be prudent to evaluate your AR's velocity using only one brand & one weight of pellets & firing 10 to 15 shots & arriving at an average.
> Finally to avoid the infringement of wind, humidity etc. 'The best environment to test an AR would be the Air conditioned / Moisture & wind controlled confines of an indoor shooting club!!!

> Happy Testing
Briha

[harshvardhan]

Mr. Basu,
A very nice Implementation of the Idea,
Finally one more thing cover your phone with Surgical Cottons and wrap with small piece of Cloth for Humming free clear sound
where peaks of Muzzle and Impact can be easily distinguishable....

[pratik_mahale]

Basu,
I think pellet will not release the barrel immediately with the firing sound it will take fraction of second more to accelerate thought the barrel that’s why we need to do follow through after firing
Plus with sound method we are actually calculating the acceleration speed of pellet from zero FPS at breech to a fix distance say 20 yards & than we calculate average speed of pellet so the error level is high

It just my thinking

[James_Bond]

Thanks Harshvardhan for sharing the post and for this interesting approach.

[Basu]

Dear Pratik,
Your observation is correct.The pellet accelerates from no velocity to max velocity within 10" from
the breech, and then it retains its velocity as air pressure from behind still continues to push it till
it leaves the barrel.So there is a initial difference of velocity is not captured in Audacity.I was wondering
about pin point sound source of the gun.To my understanding it is the breech/dead end where sound
is originated.During my experiment I opted to calculate the distance from barrel end and not from breech
area but from barrel end .Had I done that the 18" difference was resulting in 5% increase in velocity.
That is the reason I requested IFGians to calibrate this as close as authentic.The Average velocity
and muzzle velocity is taken care by the factor of 0.965 by IFGian Hrashavardhan within 30 ft, which
I am sure, he can throw better logic into that.Other factor like breeze has got some good role to play ,
unlike temperature and humidity, as it has same effect on modern cronograph in operation.
Please take your time and calibrate this most close to authenticity.

Basu