| Posted: Sun Nov 1st, 2009 12:04 AM |
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TnTom
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How much is enough?
If you use a chronograph how much weight do you think standard deviation should play in your decision to adjust a load or when not to adjust?
Do you evaluate your s.d. before, during or after you've accomplished the group that your satisfied with.
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| Posted: Sun Nov 1st, 2009 01:46 AM |
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OldStuffer
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I personally don't pay the std. dev. a lot of mind.
I, loading hunting ammo, not "10-bullets in one hole" ammo, want my total deviation for 10 rounds to be under 50FPS High to low.
I am flexible at this if that is skewed a bit by a single exceptional high, or exceptional low, or one of each, among a mass of close loads.
I am pretty sure I missed something in my loading for those.
I will repeat my loading, attempting to be more careful, double, or tripple-checking everything, and then see what happens, then decide what to do next.
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| Posted: Sun Nov 1st, 2009 02:16 AM |
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Busted
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"If you use a chronograph how much weight do you think standard deviation should play in your decision to adjust a load or when not to adjust?"
None. I adjust my loads depending on the targets. Low Standard Deviation is nice but at the ranges I shoot/hunt it's irrelivant. Accuracy is not.Last edited on Sun Nov 1st, 2009 02:16 AM by Busted
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| Posted: Sun Nov 1st, 2009 06:12 AM |
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Don Fischer
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I like a low SD but my best loads are not always the lowest. The only thing that really counts is the target. I have a cast bullet load I shot in my 30-06 that gave me a .485" group at 50yds, SD was 196! Go figure, I have no explanation for that!
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| Posted: Sun Nov 1st, 2009 06:20 AM |
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miestro_jerry
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I run a ten shot string, add them all up, divide by ten and that is average velocity.
If the bullets are impacting into the grouping I expect, then the average velocity is all I care about. It the grouping is wrong for that rifle and I plot the target against the velocity table I generate, then I have some idea of what to adjust.
If your into doing a lot of math, please be my guest. I view things in such a practical fashion that if I hit the target repeatedly in the expected grouping, then my work is done.
I am going for the Gamma Master if I can find a stocking store with some one who understand the device.
Jerry
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| Posted: Sun Nov 1st, 2009 04:03 PM |
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Paul B
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The only things I bother with are the average velocity and the extreme spread. One round Ii load for, my .375 taylor has an extreme spread of 6 FPS with the 270 gr. Hornady and 8 FPS with the 300 gr. Sierra Ggame King. Accuracy is excelent running from .80" to a hair over one inch. Not bad for a potential DGR.
Pal B.
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| Posted: Sun Nov 1st, 2009 04:48 PM |
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TnTom
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Don Fischer wrote: I like a low SD but my best loads are not always the lowest. The only thing that really counts is the target. I have a cast bullet load I shot in my 30-06 that gave me a .485" group at 50yds, SD was 196! Go figure, I have no explanation for that! Ive had similar results in that the lower sd didn't result in the tightest group but a 196 makes me think that you had an atypical in the sample.
getting some interesting replies.
thanks
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| Posted: Mon Nov 2nd, 2009 01:25 AM |
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OldManMontgomery
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A low extreme spread and low standard deviation shows the powder is burning very consistently. That is good, but it's not the whole show. A wide spread and a big deviation usually shows a lower pressure load; powder burns more uniformly at the upper range of the pressure range.
ES and SD are simply two more tools in the repertoire to develop a good load.
As has been mentioned, if the load shoots tight enough for your use, don't worry about it.
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| Posted: Mon Nov 2nd, 2009 02:46 AM |
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Dale
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Here is a good article about SD. Taken from an Oehler Manual.
http://www.naaminis.com/standev.html
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TnTom
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Dale wrote: Here is a good article about SD. Taken from an Oehler Manual.
http://www.naaminis.com/standev.html
"The secret for making smaller groups is uniformity. Other things being equal, the more uniform you can make the ammo, the more likely it will shoot to the same hole".
Thanks Dale. Probably the best breakdown I've ever read. I've been in the habit of shooting 2 samples of 10 for a specific load. Thats a sample of 20. What I will do for a while as suggested in the article is to run 3 groups of 5 a total 15 but I will load only 5 per day and shoot over 3 days. The change in wind, temp, and humidity will have additional impact on both sd, average velocity, min-max vel., and group size and compare the results to my results on the bench today. It will require a decrease in sample size with an increase in variable and a reduction in cost (I sure like that).
11/02/09
Gun:Ruger 77 MkII, Cal .220 Rocket, 1:7 twist, Walther Heavy Barrel
2 groups of 10, Distance 200 yds
Load 1 (sample 20)
Bullet Hornady 75 gr bthp Moly, 32.5 gr Varget, Wind zero
Aver/Aver Vel: 3008, min/max 73 fps, sd 28.37 and 28.57, group .576"
Load 2 (sample 20)
Bullet Nosler 69 gr bthp, 33.6 gr Varget, Wind zero
Aver/Aver Vel: 3062, min/max 80 fps, sd 25.59 and 26.16, group .375"
My conclusion is change nothing and try again.
I really enjoyed the article.
Thanks
Tom
Last edited on Tue Nov 3rd, 2009 12:14 AM by TnTom
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OldManMontgomery
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Tom, an average group size of less than .5" at 200 yards is reasonably impressive. Perhaps not a world record, but quite respectable.
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TnTom
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OldManMontgomery wrote: Tom, an average group size of less than .5" at 200 yards is reasonably impressive. Perhaps not a world record, but quite respectable.
What would be the record I wonder?
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fryboy
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depends upon the distance ...every class has it's own but it's safe to say that the longer distance ones keeps getting smaller all the time lolz the wiki states around .02 ...
http://en.wikipedia.org/wiki/Benchrest_shooting
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Bigdog57
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I do try to keep my loads consistent and keep SD as close as possible, but.....
My 7.5X55 Swiss loading is more consistent in load weight and velocities than GP11 - but GP11 still shoots tighter - there are so very many differing factors, I have not yet found the one or two that will get me to the same level of accuracy. Most likely has to do with a combination of bullet profile and seating depth - most Swiss rifle reloaders seem to think these have the most effect.
My best 7.62X54R load has equal or greater variance in velocities than the Hungarian surplus load of comparable bullet weight - but my load does shoot half the group size! So again, other factors have more bearing on accuracy than SD specifically.
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TnTom
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I have found the same thing, the lower doesn't always equal the smaller, unless maybe I had a big spread and within a similar load the only difference being a few tenths of powder or half grains the sd of 28 vs say an sd of 32 is probably more reflective of the chronograph than the difference in the load itself.
Most often I find a big sd spread is the difference in powders and probably a measurable difference in group.
It does seem to help identify a trend mostly.
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TnTom
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fryboy wrote: depends upon the distance ...every class has it's own but it's safe to say that the longer distance ones keeps getting smaller all the time lolz the wiki states around .02 ...
http://en.wikipedia.org/wiki/Benchrest_shooting
Thanks for the link.
Checked out some of the records and at the top is Mac Macmillian in 1975 shot a 5 shot 100 yds group of .009". Never imagined and I can barely comprehend it. That's about twice the thickness of a human hair.
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TnTom
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miestro_jerry wrote: I run a ten shot string, add them all up, divide by ten and that is average velocity.
If the bullets are impacting into the grouping I expect, then the average velocity is all I care about. It the grouping is wrong for that rifle and I plot the target against the velocity table I generate, then I have some idea of what to adjust.
If your into doing a lot of math, please be my guest. I view things in such a practical fashion that if I hit the target repeatedly in the expected grouping, then my work is done.
I am going for the Gamma Master if I can find a stocking store with some one who understand the device.
Jerry
I used the gamma master until I shot a low one but was there something that you wanted to know about it? They seemd to be a good unit for the money. I bought another Gamma and am trying to keep them up a little. Simple to use.
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Good groups at long range require minimal variation in velocity, as velocity variation produces vertical stringing. therefor standard deviation becomes very important at ranges over 300 yards, at 50 or 100 yards it is of practically no importance. 38 special wadcutter target loads have extremely high standard deviations yet still produce exceptionally good groups at 25 and 50 yards.
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DesertMarine
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I took this quote from the site mentioned by Dale. I like it because that explains SD and it's use in reloading better than I can.
"Some shooters question the use of standard deviation in load development. We agree that velocity uniformity or standard deviation should not be the only criteria used in selecting a load. Standard deviation must be considered along with everything else you know about the load. Note that the measured standard deviation includes variations in both the ammo and the chronograph. Chronograph systems with inadequate spacing between skyscreens often give passable readings of average velocity, but questionable readings of standard deviation. Whenever you use standard deviation, remember there is an important corollary of Murphy's law. Its regular use can replace many mathematical theorems and complicated statistical procedures.
Large groups usually repeat;
Large groups with large standard deviations always repeat;
Small groups caused by luck never repeat."
I use SD to tell me if my loading technique is consistent and I use it as a part of my load development
I load all my ammo, target and hunting to the same standards. I want to give myself every advantange I can while I am hunting. Needed, like some guys said, in hunting benchrest accuracy is not needed and I agree with them but I prefer it.
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RaySendero
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TnTom wrote: How much is enough?
If you use a chronograph how much weight do you think standard deviation should play in your decision to adjust a load or when not to adjust?
Do you evaluate your s.d. before, during or after you've accomplished the group that your satisfied with.
Tom,
I keep the following numbers for each 5 shot group run over my chrony:
the average velocity, the SD, the extreme spread and the coefficient of variation (i.e. 100 times the SD divided by the avg. ) for example:
2891, 2880, 2903, 2894, 2904
Avg = 2894
SD = 9.8
XS = 24
CV = 0.34%
Keep these numbers and the load recipe from the get go and you will find out for yourself how useful they are! People that don't keep these records will never know, but may give you advise anyway!
Last edited on Fri Nov 6th, 2009 02:18 AM by RaySendero
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