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How to Calculate Standard Deviation: 12 Steps (with Pictures)
Standard deviation tells you how spread out the numbers are in a sample. Once you know what numbers and equations to use, calculating standard deviation is simple! Look at your data set. This is a crucial step in any type of statistical...
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Its easy to do semi manually in Excel. How good are your Excel skills?
Standard Deviation Calculator
This free standard deviation calculator computes the standard deviation, variance, mean, sum, and error margin of a given data set.
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The important thing to keep in mind is, that the standard deviation is just part of the equation; Since it's an expression of the variance you can expect from round to round, it does NOT mean that you can expect every shot to be within +/- 1 standard deviation. Std Dev is used to calculate the expected velocity range for your entire 'population' of shots, which is +/-3* Std Dev, so, if your Std Dev =12, you can expect +/- 36 FPS of your mean (average) muzzle velocity. A lot of folks chase StdDev with a great deal of passion, BUT, it isn't always a direct correlation to downrange accuracy. I've had single digit StdDev shoot like hammered shit, while stuff with 24 FPS Std Dev put 10 in one, .5 MOA hole @100M, during the same range session with the same rifle & bullet, just different powders; go figure....
Depends on the use.
For stuff I’m maybe going to shoot 500 ish yards I don’t care about it at all as long as it’s not atrocious.
For my rifles I regularly shoot well past 1000 yards I’d want it in the single digits and in the 5 or better range is preferable.
Good information. Thanks. My string included a clean cold bore shot that ran faster than all the others. In fact, my notes indicate that velocity ran much closer after the first 4 shots. I'm going to fire another string with the fouled barrel and see if SD improves.
So my SD's didn't change much. I'm going to try a couple different primers. I'm beginning to shoot at longer ranges (out to 1K). I'm making hits but as my skill level progresses I want to make sure I'm not being handicapped by my equipment. Any other suggestions?
A 1 moa rifle with an SD of about 10 will do quite well at 1000 yards.
At 1000 with my 260 and summer DA I’m at 7.77 mils
a shot a 20 fps drop is 7.91
Not much.
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One thing to note, standard deviation is a statistical measurement that requires a statistically significant dataset. A lot of SDs that are touted on the internet are based on 3 or 5 shots that make guys feel good. Kinda like snapping a picture of that 3 shot clover that happened once and claiming a quarter minute rifle.
I like tracking SD mainly because I like running numbers. But to me, trigger time is far more valuable than chasing SDs at the bench.
I like tracking SD mainly because I like running numbers. But to me, trigger time is far more valuable than chasing SDs at the bench.
Based on a Gaussian distribution, +/-1 Standard Deviation statistically represents 64% of typical outcomes around the mean. +/- 2 standard deviations is 95% , +/- 3 standard deviations is 99.7%. I think what Secant said is important on sample size.
In shooting it's basically used to determine consistency of velocity which will translate to consistency of vertical dispersion at distance. I guess I haven't noticed much correlation between dispersion at 100 yards and SD, but at 1k it can be apparent.
Kind of the rules of thumb I've gone by is under ~10 is what you're going for on a 10 shot string and there will not be a ton of noticeable difference between a SD of 10 and an SD of 4. Only the amount of money it takes to get there
If you're at 12 now I don't think you'll have any problems at distance.Thanks everybody. I needed to have this put into perspective. The rifle in question consistently shoots 1/2 and better MOA out to 300 with this load and an SD of 12. That's as far as my local range goes. I only get to shoot to 1K about 4-6 times per year. So, given what Steelhead said, I'll give different primers a try. If it works good but if not I think I should leave it be unless I find a place to shoot past 1K. This was and expensive rifle for me and I don't want to burn up a barrel chasing numbers when I can be enjoying shooting the damn thing. This shit can drive you nuts!
I suggest you end your load development efforts immediately.
1/2moa and 12sd is more than acceptable for 4-6 range trips to 1k... Some people just love chasing better sd/es numbers and can go nuts doing so
So I was at the range today. Had my pet load for the CTR but loaded with different primers. Shot them at 200yds. One of the primers, CCI BR-2, gave me an avg of 15 fps more and lowered my SD to 10 over 20 shots. My 4 group averaged 1.15 inch. Very pleased with both my set ups now. Time to stop playing and start shooting.
Or build another one?
Or build another one?
10-15 or better.
Read this article because it has a lot of info and will answer your question regarding what level of precision SD plays in hit probability.
That's funny! BR2's lowered my velocity by 10-15, and narrowed my SD by 3-4 fps in my pet load compared to 210M primers.
Just read the article. It does put it into perspective for me. Helps me arrive at the conclusion that I'm happy with my results and don't need to go any further for my typical shooting.
Exactly. I was chasing the SD and velocity dragon for a long time. I have since stopped doing that bullshit because realized I'm not a benchrest shooter. As long as things are sub 3/4 MOA and under 15 SD for a 10 shot string, I'm loading a shit ton and focusing on my shooting skills.
I agree and a tight sd is nice but guys get so focused on a SD of 3 that they never run the numbers between a 50fps velocity swing at 1500 yards... That one or two outlier may not be enough to blow up your sd for 10 shots but a .6 mil drop change from shot to shot is a no go chief. I focus more on my es being under 35 fps consistently at a given da and temp.
Correct. ES of 35 and under, and your doing well.
Extreme spread is technically the difference between the highest and lowest values in a data set.
What really matters in shooting is the velocity change from shot 1 to shot 2, from shot 2 to shot 3, etc, etc.
What really matters in shooting is the velocity change from shot 1 to shot 2, from shot 2 to shot 3, etc, etc.
Read The Perverse Nature of Standard Deviation by Denton Bramwell. It's a short paper on Standard deviation that every reloader should read.
If it's getting you pulling your hair you really need to read Bramwell's paper.
So, I just googled that paper, and it really fell apart in the first page were he says that small data sets can reliably convert ES to SD based on simply multiplying a coefficient. He uses dataset examples consisting of 2 to 7 data points.
I’m only an engineer, but performing any sort of statistical analysis on two data points is just a really bad recommendation. His credibility took a nose dive for me anyways.
I personally don't "savor" anything over an SD of 8. Won't go into the POI deviations between the different numbers, but below 8 provides a decent calculated hit probability at 1 mile for 338LM. I consider success at SD 8 or less across 10 shots.
It depends on what your intentions are though too. If you only have a 1K range then just run it.
D
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Jesus Christ, =stdev()
