Obsessive reloading question

[lrrifleman]

Hello!

For those of you obsessed with accuracy and chronograph either your purchased or handloaded ammo, do you find that smaller (read single digit) standard deviation numbers are indicative of a potentially more accurate load than a higher level of standard deviation? I know that this is what I look for when I build my loads for my match rifles.

Thanks in advance for your help!

 

[OKFC05]

Not necessarily for handgun ammunition because of the shorter ranges usually involved, and other factors that may dominate the achieved accuracy, like the deviation induced by the shooter shooting offhand, or a service pistol's loose tolerances.

A 1" load in a 3" gun with a 4" shooter still gives 4" achieved accuracy. A 3" load in the same setup would look the same on the target. Action pistol games are different from long-range precision shooting. Score is effectively points divided by time.

 

[thadheth]

Perhaps your question is more complex than it appears. IIRC standard deviation is a measure of the statistical probability (expressed as a percentage) that any given shot will fall within that range from the average; therefore, the smaller the standard deviation, the more "accurate" the load. It's been a while since I have calculated standard deviations, but as I recall, the probability is 86% that a shot will fall within one standard deviation and 98% for 2 standard deviations.
Again, perhaps I am oversimplifying your question. And, if my recollections of standard deviation are incorrect, one of our resident statisticians will be along to correct me.

 

[alwslate]

I'm not obsessed with accuracy but I might be obsessed with consistency.
Almost all of my handloading is for handguns and I chronograph every
load. To me an efficient load is one with a low extreme spread. I don't
bother to calculate std. deviation. I like to see ESs of no more than 20 fps.
This isn't always possible but I like to try.

 

[rockquarry]

This has become a sort of Internet fad. It certainly hurts nothing to check the numbers, but, if you're getting good accuracy at whatever distance you're shooting and the numbers aren't "wild", they mean little. Small SD numbers show consistency only; consistency doesn't necessarily translate into accuracy. Along with extreme spread, these are often pretty much sterile textbook figures.

However, if I was attempting to shoot small groups at 500 yards or farther, I would at least do a cursory examination of the aforementioned figures when working up loads. Seems to me they might have some meaning then, but no guarantees.

I work up a lot of handgun and rifle loads and have for years. I always use a chronograph in doing so. I seldom look at the deviation numbers.

 

[dave1918a2]

When I load for My 1000 yard match rifle, I chronograph the loads and pay attention to extreme spread more than SD. My 190 grain load has an ES of 6fps and a SD of 6. It is more accurate than My 200 grain load with 14fps ES and SD of 3. The cartridge is a 30 - 338.

 

[Sevens]

Another bit I would add to a quality discussion thus far...
If someone is saying that they have either a low SD or ES, I really want to know the sample size or I'll write it off as noise.

I'm not a huge fan of chronographing loads, partly because it's royally tedious and partly because I have lousy equipment... and one makes it difficult to improve the other! I have a Chrony Beta Master and I have many complaints, and this isn't the discussion for all of those complaints, but one of those complaints is wholly relevant:

this unit seems to be mathematically capable of guiding Apollo 11 to the moon and back without help, but it limits ALL of it's calculations to 10-shot strings.

Back to my original point... if you tell me that you have a low ES and low SD, I'm listening... to find out the sample size. 10 shots is a lousy sample size. If I were chronoing loads and looking for a winner and I found something that gives me a low ES and SD in 10 shots, the only conclusion I come to is that I need to continue to 20, 30, 50 shot sample size.

Chrony won't let me. Other, better units will let me. If I lived on some land and could should safely and set up a chrono within steps of the back door, I'd make a fantastic project out of this. But I don't, and so tossing money at a better chrony and losing fantastic range trip to a fun-sucking chronograph is not on my list of stuff to do.

Great discussion, though!

 

[Drm50]

I've been loading for over 50yrs. Closest I come to Match is Varmit guns.
I do go for extreme accuracy but have never really worried about velocity being + or - a few FPS. Handgun ammo I approach same way.

 

[DWalt]

There are actually two different SDs in play- the sample MV SD and the population MV SD. Say you fire a 10 shot sample. You can calculate the SD of that sample, but it does not necessarily reflect the SD of the whole "Population", i.e., an infinitely large number of shots fired under identical conditions. There is usually a mathematical correction (n/n-1) made to the sample SD calculation to more closely estimate the population SD based upon the small sample of events, say 10 shots. Typically those chronographs which internally calculate SD automatically perform that correction and that is what is displayed on the screen. A corrected sample SD, even if only 10 shots, will provide a fairly good estimate of the population MV SD. Whether the magnitude of the MV's SD (or the sample MV ES) correlates closely with group size (in terms of average group extreme spread) is another question entirely that is not so easily answered as there are other possible confounding considerations.

What most shooters fail to recognize is that if one REALLY wants to know the "accuracy" (really it's called precision) of a given ammo/gun/shooter combination, it is nearly impossible to do so with fewer than 50 shots being fired, preferably at least five 10-shot groups. Five-shot groups are essentially worthless in providing such information as there is far too much group-to-group variability.

 

[lrrifleman]

A!low me to are some additional information.

I am attempting to rebuild an accurate match load for my Springfield Armory Trophy Match. I had a good load for it before my accident, but had trusted it to memory, and that was lost with the concussion.

My goal is a consistent 3" group or better at 25 yards using both a cast 200gr SWC and a 200gr TMJ/Plated SWC. I have no aversion to shooting anywhere from 10-25 round test groups (repeatedly). I am not motivated to fall within a major/minor power factor category, I just want to build a consistent and reliable load for both NRA Precision Pistol and CMP Leg matches.

 

[fredj338]

Hello!

For those of you obsessed with accuracy and chronograph either your purchased or handloaded ammo, do you find that smaller (read single digit) standard deviation numbers are indicative of a potentially more accurate load than a higher level of standard deviation? I know that this is what I look for when I build my loads for my match rifles.

Thanks in advance for your help!

Maybe. Accuracy is a function of several factors, small vel dev is only one. I have had really high vel SD but the load shot great. I have also had really small SD & the load shoot poorly. In rifles, bbl harmonics plays a huge roll & that wont show up on the chrono. The target never lies, so trust how the load shoots & live with the extreme spreads or higher SD. You can burn a bbl up chasing numbers.

 

[gwpercle]

I read many handgun shooting / accuracy articles in gun magazines and have noticed in many instances the loads with the lowest sd's are seldom the most accurate . Some loads will have single digit numbers and not be nearly as accurate as a load with double digit numbers.

After seeing this time and again... I just ignore those numbers and see what groups best on the target...that's what accuracy is about in my book, tiny little one hole , clover leaf groups in the X-Ring , not a sd number on a machine .
Gary

 

[Drm50]

A buddy of mine bought a Springfield in late 70s or early 80s. I don't remember what the name of the particular model was but it was whatever was top of the line at the time. A book came with rifle with suggested target loads. The Speer 130gr HP was one of the bullets recomended. It was a one holer at 100yds. I had shot 150gr for years as my accuracy load in BAs. I tried the Speer 130hp and shot the best groups consistently that I ever did. I switched to 130hp but it may not be the best for long range.

 

[Big Cholla]

Since there are such a large number of variables that affect the accuracy (point of impact) on each shot, I find that many if not most of them far out weight the final result over that of SD. I have a heavy barrel prairie dog rifle in 250 Ackley Improved that shoots most any load under .350" for three shots. The very best load that I use when the Wind is reasonable has almost twice the SD of the very best SD load recorded. It is a consistent .275/.300" performer while the best SD load struggles to average .400/.425". The higher SD load is the heavier weight bullet, so I use it in very windy conditions. Long way around for me to suggest to you to not obsess about Standard Deviations, ........ IMHO.

 

[scotthickoryky]

deveation doesnt bother me at all,,,, accuracy in pistol i like to be decent groups but not a deal breaker,,, now in rifle different story,,,,, i like consistancy over everything ,,, when i shot comps that was a differnt ball game,,,,,, round to round i loaded i made sure EVERYTHING was identical even then case weight,,, now that i am over the hill and i reload and shoot for fun i am not that pciky