Pellet velocity without Chronograph( pretty accurate.) Chronograph verified

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Dave

Dave

Member
Jun 20, 2015
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Ohio, United States
Today I was re-sighting my .25 Marauder and thought I would try something different. My chronograph is dead and I need to purchase a new one before too long.

So here is what I did:
First I sighted in my rifle at a known distance(55 yards) with the help of a laser rangefinder. Next I put zero data and an educated guess on pellet velocity into chairgun pro program to give estimated holdover for the next part. Then I Shot a group at a further known distance (112 yards) and compared impact to Chairgun table. Finally I adjusted the velocity in the program until it matched impact point of shot group.
I was wondering if anyone else has done this or how accurate it could be. I know this is not a replacement for Chronograph, but I was in a pinch. Lastly any advice on a good chronograph? something that can work well in most lighting conditions.

Thanks Dave


To follow up on this I just got my new Chronograph and light kit, thanks ajshoots on that suggestion. It works like a charm in my basement, Anyway from my above method I predicted a velocity of about 840fps(JSB Kings). Which I think is kind off disappointing from the manufacture tune. So with a fill from about 2750 my first 8 shots high 832 low 825 average 827. My next eight really started to drop off more, low of 796 on shot number 16. Anyway my prediction was only off by about 13fps.


 
Not sure how close you can get to the actual velocity by your described method? Should get you close I would assume. I really like the Competition Electronics Pro chrono with the CE IR lighted screens. This setup allows use in my shop or outdoors with repeatable accuracy and I have yet to get an error in almost a year since getting the Pro with IR screens.
 
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That is how some of the powder burner guys do it, including some sniper instructors like Todd hodnett.
According to them the drop of the projectile is the drop, no matter how you look at it ,when you match your drop to the velocity in a ballistcs program that's what your true velocity is. I should mention todd hodnett works closely with Brian litz, and Brian is a rocket scientist, literally. Hope this helps.
 
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ajshootsNot sure how close you can get to the actual velocity by your described method? Should get you close I would assume. I really like the Competition Electronics Pro chrono with the CE IR lighted screens. This setup allows use in my shop or outdoors with repeatable accuracy and I have yet to get an error in almost a year since getting the Pro with IR screens.
Click to expand...


Does the indoor lighting kit work well? I have 12 yard test range in basement and there is only a few dim lights in my bench area
 
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After having shot long range with powder burners for about 8 years your method is exactly how I do it. Only the very best chronographs are actually accurate anyways and vertical dispersion will tell you when your rifle is not being consistant enough. Most chronographs can be off by 10% and they say that in the instructions.
Jon
 
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You can download the Croni Connect app to your smart phone or iPad. It's a free download and I use it in conjunction with my chronograph and it seems to be mostly consistent with my crony, you just have to set it up right. 
So you don't have to rush out and by a new chronograph, instead you can use your smartphone or iPad as a chronograph instead.
Skip
 
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Dave, I have used this method since I got the Hawke ChairGun app.
You put in what you KNOW, and what the gun TELLS you. 
You know: 1: Distance between sightline and muzzle
2: the pellet specifications (the program gives you this).
3: the distance to the second zero, in the program called far zero. (when shot and sighted in that is)
The gun tells you: The drop of the pellet between the far zero and the next distance. 
Then you manipulate fps in the program until it matches what the gun has told you. 
The rest gives it selves. In fact it is based on the facts - isn`t it?


 
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Gunnertrones you beat me to it. An you explained it better.


I have used a method similar to this quite a few times.
After zeroing your rifle at your preffered distance (likeley somewhere from 40 to 50 yards) enter all the nessasary info into Chairgun or whatever program you use. (Pellet BC, Scope height, ect) You can make an estimate of what you reckon the velocity should be.
After you are confident with your zero you can extend yoir target to 100 yards or further (The further the more accurate your velocity calculations will be)
DO NOT ADJUST your scope hold over at all. Shoot as if you were shooting at at your zero distance. Then you measure the POI change from the center of the target (where you were aiming)
You can then use your balistics program to see what the POI change should be at the velocity you guessed and the range you shot at (I used 100 yard as an example)
You then change the velocity on the program until you get the POI change that you meaured on your target.
Remember: The further the second target is the more accurate you will be able to get the velocity
You have to measure the distance to target (rangefinder) and POI change very accurately otherwise the velocity will be incorrect.
With this method you can come bloody close to the real thing.
 
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Finally got to test tables out today almost no wind. I took a few shots at different ranges using both holdover and under before the final test. I was kind of surprised how well it worked, and I can add a new longest confirmed kill to hunting post(133 yards using table ).

I have ordered CE Pro and indoor light kit, Chrono always a good tool to have to tune gun. I plan on purchasing a much better rifle next spring(saving up and waiting on a few new guns to hit market) so I know this Is better gotten now than later.

davidbotha- I know it's better to not use holdover, but my known 112 yard target was a tree stump that didn't give much vertical room. My educated guess was to see what people had chronographed their stock gun at with jsb kings and use similar starting point. The hardest part is trying to eliminate as much of the human error as possible.

 
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There are also mobile applications you could download which uses speed of sound and distance to target/muzzle to calculate muzzle speed.

The major downside to using a ballistic program is the variations in BC.

BC itself is calculated using projectile speed at different distances from the muzzle, to estimate the true nature of the projectile.

The issue with this method is that, BC already has estimated muzzle speed as an input, and it varies depending on exact external conditions and the pellet itself.

So basically you have something starting from a estimation, added with external uncertainty, and you are estimating again using the program, your result could fall anywhere between wildly off target to spot on. It might appear you are getting good results a few times, but if you start using a fixed BC, and do this 100 times, you are likely going to get a bell curve out it.
 
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