Chronograph readings?

nevanevan

nevanevan

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Curious how many shots you will run through a chrono to establish your data. You hear of people getting really low SD's, is would say <10 is pretty ferken good, so I question how many rounds they used for their sample. I somewhat doubt they are running 100 rounds through a chrono and getting number like this.

Please fire away with your experiences.

Evan
 
Considering

Accuracy: 99.5% or better. Displayed velocity will not differ from actual velocity by more than 1 part in 200, i.e., ±10 fps on a velocity reading of 2000 fps

For Shooting Chrony.
 
I would never shoot 100 rounds for 1 charge load, I make sure I am picky about the test loads. I did however shoot 80 rounds through the Chrony last weekend for my 357mag. Only 5 shots each. You can still get decent results. (I don't shoot my rifle more than 650yards yet either)
I had more trouble with the sun/cloud than the ammo. Had to shade the chrony completly and shoot the 357 when the sun was out, 9 mm when the clouds were in the way.
 
Traditionally, it's five shots over the chrono to get what is considered an honest test.
However, it depends on what you are looking for. I usually use it to get the bullets going up to the speed they were designed to go in that calibre. For example, a lifetime of 30-06 data is considered 2700 fps for a 180 grain bullet. If I check two of a new load and get about 2560 fps, I quit and put about 2 grains more powder in my next test reloads.
When you get up near the velocity you are looking for, it's nice to test five, for greater accuracy.
 
My Unique 357mag results were close enough with just 5 rounds each. I will post actual results when the sun comes up. Over the average of 5. It worked out .1 grains of powder = 10 fps. The jump was close for 6.9gr-7.0, 7.0-7.1, 7.1-7.2,
 
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...when working up a load i do so in 3's ...i record and spot each shot ...if i get more than a 20 or 30 fps deviation over the entire set of 3 and the shot is a flier then i reload that set and shoot again ...i prove loads in sets of 5's with a chrony ...this is for hunting and MOA accuracy if the rifle is capable of such
 
legi0n said:
from a statistical point of view, less than 10 readings is not robust enough.
Click to expand...
I am not a mathematician, but I have shot 10 loads and they have all been within 15 fps, which is inside the accuracy of the instrument at 3000 fps, why shoot any more?
 
22to45 said:
I am not a mathematician, but I have shot 10 loads and they have all been within 15 fps, which is inside the accuracy of the instrument at 3000 fps, why shoot any more?
Click to expand...

10 loads or 10 rounds of one load?
You see, everyone is averaging the velocities and computing the SD (standard deviation) and then the extreme spread.
But the SD is not really meaningful for less than 10 readings and that's because of chance.

For example, today I shot a 5 hole group.
The first 3 bullets went into the same hole but the next 2 went 1" away.
Could I have declared myself satisfied with the first three shots? No. It just happened they went in the same hole (that's the chance part). 10 or more shots will give the real picture.
 
legi0n said:
10 loads or 10 rounds of one load?
You see, everyone is averaging the velocities and computing the SD (standard deviation) and then the extreme spread.
But the SD is not really meaningful for less than 10 readings and that's because of chance.

For example, today I shot a 5 hole group.
The first 3 bullets went into the same hole but the next 2 went 1" away.
Could I have declared myself satisfied with the first three shots? No. It just happened they went in the same hole (that's the chance part). 10 or more shots will give the real picture.
Click to expand...

I share the same sentiment. I believe that you need a sample size of at least 10 rounds to get an idea of the velocity.

On the question of velocity, how far from the muzzle would you say is the most accurate reading? From a distance of about 20feet to 10 feet I was getting about 40fps difference in my readings which would be significant at a greater distance
 
Ok finally got a chance. 357 mag
Test 5, 6.9gr FPS 1st 1093, 2. 1145, 3. 1129, 4. 1127, 5. 1117 Average 1122 +
Test 6, 7.0gr FPS 1. 1136, 2. 1133, 3. 1142, 4. 1126, 5. 1127 1132 .1grain=10fps
Test 7, 7.1gr FPS 1. 1135, 2. 1140, 3. 1142, 4. 1157, 5. 1141 1143 .1 grain=11fps
Test 8, 7.2gr FPS 1. 1156, 2. 1150, 3. 1164, 4. 1148, 5. 1140 1151 .1 grain=8fps

I have not checked any of these for accuracy yet, but they all looked promising. Will likely try less powder next time out to get data as this was supposed to be a soft load, not the mag loads.
 
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nevanevan said:
I share the same sentiment. I believe that you need a sample size of at least 10 rounds to get an idea of the velocity.

On the question of velocity, how far from the muzzle would you say is the most accurate reading? From a distance of about 20feet to 10 feet I was getting about 40fps difference in my readings which would be significant at a greater distance
Click to expand...

I always measure the distance from the muzzle to the chronograph and use a ballistic program (point blank) to calculate the real muzzle velocity.
 
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