Acceptable ES & SDs for Competition

[Jordan Smith]

Useful? Yes, absolutely.

 

[Mystic Precision]

True enough. When ironing things out as a new shooter, say for example you've never reloaded before and now your trying your first batch of handloads, do folks think a chrony is a somewhat useful tool in trying to figure out if you are on the right track?

Yes, extremely useful tool.

Let's a newbie know when they are over the redline.

Beyond that, you take the numbers as you see fit.

I like to get a feeling for what the performance expectation should be (ie reasonable velocities). Verify when working up a load that I am within expected boundaries, then tune for best performance.

As I said earlier, I use a chronie to make sure I am not going to run into the danger zone. Beyond that, holes in paper tell the tale.

Jerry

 

[Longshot]

Excellent. So as a "newbie" then having a chrony and using its data,eventhough we know that it may not be 100% correct, is still a good idea. Good stuff!

 

[atr]

For those that don't know how to find the SD (Standard deviation) this is how I do it. Feel free to chime in if you have a different way.

1.Fire a string of shots over a chrony and record you speed for each shot.For this example lets use ten shots.
1.3012
2.3022
3.2999
4.3007
5.3011
6.2998
7.3008
8.3002
9.3031
10.3014
2.Find the average of those 10 shots. Do this buy adding the speeds of all the shots together and then divide it by the number of shots you fired.In this example divide by 10.
1.3012
2.3022
3.2999
4.3007
5.3011
6.2998
7.3008
8.3002
9.3031
10.3014

Total 30,104/10
3010

3.Now using the average speed (3010),calculate the number of fps it would take to either add to get to your average or subtract from to get to your average.

1.3012=2
2.3022=12
3.2999=11
4.3007=3
5.3011=1
6.2998=12
7.3008=2
8.3002=8
9.3031=21
10.3014=4

4.Now take those numbers and find the average by adding them and dividing by the number of shots.

1.3012=2
2.3022=12
3.2999=11
4.3007=3
5.3011=1
6.2998=12
7.3008=2
8.3002=8
9.3031=21
10.3014=4

Total 76/10= SD of 7.6

5. To find the ES(Extreme Spread) count the number of fps between the slowest and fastest shots

Slowest was 2998
Fastest was 3031

ES= 33

http://easycalculation.com/statistics/standard-deviation.php

 

[Mystic Precision]

Excellent. So as a "newbie" then having a chrony and using its data,eventhough we know that it may not be 100% correct, is still a good idea. Good stuff!

Open any number of reloading manuals from major companies. Look at the real common cartridges like 223, 22-250, 308, 30-06, 7RM and 300WM. Bread and butter stuff.

NONE OF THEM AGREE - unless they happen to be reprinting someone elses data.

You have variations in components, test barrels/rifles, and they all say NEVER EXCEED THIS DATA. how often do you see one max is anothers mid or near start loads?

And all these receipes can change from volume to volume, brand to brand.

For a newbie, with the fear of death or worse, that is confusing and intimidating. And why we get dozens of the same question - "Where do I start?".

However, look at the same data and ALL agree on the muzzle velocities within 100fps for any cartridge bullet weight combo in the average test barrel length. Aha, something that we can work from and build a baseline with.

So now, with a working chronie, a newbie can use any start load and IN THEIR RIFLE WITH THEIR COMPONENTS, have a good idea where they are starting from.

If say a 308/168gr load indicates a max velocity of 2700fps from a 24" barrel and your start load is 2500fps, room to go.

however, if you take some "best receipe" off the net and you see 2850fps out of your 22" sporter. Pressure signs or not, this load is hotter then expected. Caution is warranted.

The chronie is a very important tool for any experience level and for wildcatters, paramount to safety. Yes, you can get the same velocities with both really high or low pressures depending on all the other rifle/components parameters but the average newbie is going to be using standard stuff so no magic loads to be found.

YMMV

Jerry

 

[Longshot]

Good stuff!