velocity variations

[sturgeonhunter]

Hello. I have been reloading for 18 years and for the first time yesterday I shot over a chronograph what is the typical variation in  a loads velocity the lowest was 2655 and the high was 2685 is that typical and acceptable.this was the spread for 10 rounds. Thanks guys

[stimpylu32]

If your only seeing a 30 fps SD in 10 rounds = WOW , I have shot 10 round groups that were as much as 150 fps SD .

So , yes those numbers are more than exceptical , just remember , not all your loads well do so well . 

stimpy

[sturgeonhunter]

Thanks stimpy

[Catfish]

Almost correct, your ES, extreem spread is 30, you SD would be alot less. That is exceptional.

[Siskiyou]

I do not think your results are out of whack, I think you have a good load.  For example I had the follow Maximum spreads with two commercial loads from the same rifle on the same day.

Federal 243 100-grain SP maximum spread 45 fps.

Remington 243 100-grain C-L 80 fps. 

Handload using 105 grain Speer Splitzer 30 fps.  WMR powder
I selected the 105 grain Speer to load for deer and set aside 40 rounds in new WW cases based on the results.


Handload with 100-grain Nosler SB with H414  42fps

Handload with 100-grain Nosler SB with H414  7fps.

Extreme spread is only one factor in the selection.  Within the firing may be rounds that were very close together.

The extreme spread of the 100-grain Federal and the 100-grain handload with H414 and the Nosler solid base was within 3 fps.  And the velocity was very close.  If I was to go with a 100-grain load, it would be the handload because it is slightly more accurate. 

Getting old and shakee.

[stimpylu32]

Almost correct, your ES, extreem spread is 30, you SD would be alot less. That is exceptional.

BRAIN FART 

Catfish is right , it should be ES , the weird thing is that I have had loads with low ES that shot like shotgun patterns , while some loads that have high ES grouped very well . 

stimpy

[sturgeonhunter]

remember I'm new to this chronograph stuff what do you guys mean by sd I know es means extreme spread

[Siskiyou]

From Chrony:
“
Standard Deviation, population, (-Sd-)   
 
Multiply the square of the average velocity by the number of shots and deduct it from the sum of the squares of all shot velocities, then divide this total by the number of shots minus 1, and then take the square root of this figure.
For example: [(29902 + 30102 +29962 + 30042 - 4 x 30002) ÷ (4-1)]½= 9 FPS
Standard Deviation is a measure of how close each shot’s velocity will be to the "average" shot. It is called STANDARD because it is computed in such a way that it has a standard meaning when compared to the NORMAL CURVE. Nearly all things we measure fit a normal curve [such as the height of people, the diameter of (supposedly) identical motor pistons, and the velocity of (supposedly) identical cartridges]. The NORMAL CURVE shows that all variables occur more frequently at or near the average, and less frequently as they deviate further from the average. We use a STANDARD Deviation measure so that all things we measure can be compared with each other and to this curve [68% of all things we measure falls between one standard deviation above or below average, 95.4% falls between two Standard Deviations above and below the average, and 99.7% falls between three Standard Deviations above and below the average]. Thus, Standard Deviation is a universal method in statistics and measurement for dealing with and interpreting data.

Therefore, if the bullets are traveling at an average velocity of 3000 feet per second, and there is a Standard Deviation of 20, then 68% of the shots you fire will fall between 2980 and 3020 fps, and 95.4% will fall between 2960 and 3040 fps. Nearly all of them (99.7%) will fall between 2940 and 3060 fps.
Since Standard Deviation is the most important information your chronograph can give you, it is useful to understand the reason for this. At least ten (10) shots are required to obtain a reliable average and Standard Deviation. Fewer shots (such as 3 or 5) are typically "small samples", and are considered unreliable when measuring anything variable.”

[sturgeonhunter]

you guys are alot of help I understand now Thank you and happy reloading

[shot1]

I just punch the buttons on my Bata Master chrony and it gives me the SD and ES. I don't have to hurt my head trying to figure all the square root into whatever stuff. 

Like has been said I have had loads that shot as tight as could be and the figures were way apart and I have had figures really close and had shotgun patterns. I mainly use the chrony to help me understand velocity of accurate loads to help with the zero at longer ranges. How much to put on a scope to hit point of aim.