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Working up a new load for my 300 Win Mag today I got some info from the chrony. 2904 HI, 2861 LO, 2888 AVG, 43 ES and 16 SD from a five shot string. I get the extreme spread but the standard deviation has me stumped. What is it telling me and how do I manipulate my loads to change it?
Hmmm..
I understand your question, but imho..... I wouldnt worry about anything other than knowing what the speed is of your projectile is.
I was inquesative yrs past about getting down to the natt,s ass about chronographic readings but as time went on, I realized something: Bottom line. Once youve completed your ladder testing and develop,d an accurate/consistant load giving you .25-.50 patterns at 100 then you take that load , take 5 shot average reading from your chronograph and use that given speed as input to calculate drop and deviation via ballistic calculators. Keeping in mind to record the outside temp while chronographing.
(for me) I wouldnt worry about SD or ES especially if the propellant your runnning is showing consistant and accurate results on paper. All you can do is keep loading exact amounts of any given propellant and pray that it always burns the same rate everytime.
I hope I help,d in some way...if not?....then please excuse my rambling:o
Standard deviation is a number that describes how closely your set of values cluster around the mean (average), with the smaller the sigma (standard deviation) the tighter the cluster. Unless you have fired a very large number of rounds, however, it isn't too useful. For most shooting/handloading situations, the extreme spread is a more readily useful number. Theoretically, a small sigma should translate into a tighter group; however, experience says that this is not so.
That's where I'm at so bear with me. I'm also very new to this rifle shooting/reloading thing so I'm much like a sponge when it comes to learning and understanding everything involved.Quote:
Originally Posted by eddiesindian
I'm starting to understand which leads in to this question. What steps/changes in the loading process or components will help tighten these numbers?Quote:
Originally Posted by Pilgrim
IMO...all you can do to tighten up #s is make sure that all of your powder charges are exact, every single one. including same brass,match primers/match bullets/same barrel temps, cleaned/semi clean barrel/outside temp. etc...
As I mentioned before. To me, its more important to do your homework on working up loads thru ladder test and work on figuring out how much propellant, what brand, how much,which projectile,which weight of projectile works best thru your barrel.
As You can ask any reloader, theres no better feeling than shooting 5 rds at 100yds and the results are 5 holes touching each other...when that happens?...you break out your chrono and see what the "majic" speed is.
Good luck
This is spot on. I work up the load that's most accurate in MY rifle, using assorted powder, bullet, and seating depth combos. When I hit the one that shoots 1/2" (usually less), I'll chrono it for purposes of drop and windage charts. The FPS is what it is.Quote:
Originally Posted by eddiesindian
I ended up with Berger 80gr VLD's over Varget, with the OAL just kissing the lands. That has given me a best 5 shot group of .210" @ 100 yds. After all that, I used a chrono to see 3050fps. Now I know my 600 yard drop and can calculate for the wind.
The best you can do to have good numbers on a chrono is to be consistent in your loading procedures.
Consistent brass prep, charge weight, seating depth and neck tension are all I ever worry about.
The load ladder i am doing now has pointed to somewhere around 76 gr. which is what I got those numbers with. It shot just under 1" @ 100 yd. I have loaded a few five round groups at 75.5 and 75.8 just to see what happens. IMO, I am very consistent in my loading process with the exception of neck tension. How do I Know what my neck tension is?Quote:
Originally Posted by Texas Solo
Hi. I have an Oheler 35P. For your SD to be statistically valid, you need to fire a minimum of 32 shots. If you google Statistics you will find more info than you could ever digest. Trying to determine SD from a few shots will be as effective as using the average......
ron
ex-IBM PE
I did a quick google search on SD but nothing that came up really pertained to the bench. It was a bit over my head greek.
I simply measure a resized case neck, then a case with bullet seated. The difference is your neck tension. I get .002" consistently.Quote:
Originally Posted by IUOE
roger that tx solo....
If you use the same name brand, you usually get equal neck tension from case to case as far as neck tension.
another no brainer as far as neck tension, is that you can actually feel the difference while pressing the projectiles into the case via your press.
I know for a fact that I can feel the difference when im running winchester brass compared to lc brass.
The feel is more prevelant when you collet/neck size your brass only
Sort of. Standard deviation is used to predict the behavior of a larger group based on a small sample. In our case, to predict the extreme spread of a large number of shots based on a small number of shots. SD isn't really more or less important than ES. Which is more important depends on the sample size. If you want to know how 100 rounds will perform after you've fired 10 rounds then the SD will be a much better predictor of how the next 90 rounds will perform than the ES will. If you've fired the whole 100 rounds then there's no need to use the SD to predict the ES.Quote:
Standard deviation is a number that describes how closely your set of values cluster around the mean (average), with the smaller the sigma (standard deviation) the tighter the cluster. Unless you have fired a very large number of rounds, however, it isn't too useful. For most shooting/handloading situations, the extreme spread is a more readily useful number. Theoretically, a small sigma should translate into a tighter group; however, experience says that this is not so.
[QUOTE] For your SD to be statistically valid, you need to fire a minimum of 32 shots.[QUOTE]
How did you come up with 32? The size of the sample determines the confidence interval that the SD will predict long run behavior. A 5 shot sample is perfectly valid statistically, it's just going to have a lower confidence interval than a 10 shot sample.
The extreme spread (range) is calculated as max - min, so it is based on two numbers. The standard deviation is calculated using all of the numbers, so it is a more "robust" statistic. If you want to use a statistic to characterize variability, the SD is more robust than the ES. You can use either for similar calculations, but the SD can be utilized to a much greater extent if you are into statistics.
So It's Kind If A Measurement of Consistency?
i wouldnt recomend counting on the velocity information from your chronagraph as being gospel.
use it as a guide only for fine tuning by (actual) shooting at vatious distances. quite often the information
will be flawed. compare your actual information to your balistic program to make adjustments in velocity numbers.
it is what it is and not what some machine says it is.
Yes, both the ES (range) and SD are measures of variability. Of course as mentioned so far, the variability of your shots is the most important aspect. The same statistics (ES and SD) can be used to characterize group size, and how the group average moves as well; this is more important for hunting and shooting bulls-eyes than group size.Quote:
Originally Posted by IUOE