what would be considered good standard deviation and spread for shooting 6 or 700 yards?
standard deviation
- Thread starter model 12 toby
- Start date
I try to get it down to single digits. Below is a recent .308 load series with RL17 and 208 A-Max. I will typically take the best one or two loads and shoot four or five five-shot groups to validate the combination.
High Low Avg. ES SD
2579.5 2564.5 2570.9 15.0 6.7
2601.4 2585.0 2593.5 16.4 7.6
2642.8 2614.2 2625.5 28.6 11.7
2653.2 2639.7 2647.9 13.5 5.8
2673.2 2659.8 2666.3 13.4 5.0
High Low Avg. ES SD
2579.5 2564.5 2570.9 15.0 6.7
2601.4 2585.0 2593.5 16.4 7.6
2642.8 2614.2 2625.5 28.6 11.7
2653.2 2639.7 2647.9 13.5 5.8
2673.2 2659.8 2666.3 13.4 5.0
Obviously the lower the better. You are doing well to get into the teens for ES and single digit SD as Steve said. Occasionally someone will get into single digits for ES but this is rare and a great result and generally requires lots of work (annealing, turning, flash hole, primer pocket, weightt sorting shells, bullet sorting on Bearing surface length and meplat etc etc plus the right bullet, powder, primer combo.
Calculations for a 155 gr .308 Sierra Palma doing 2900fps vs 2880fps will result in (at 700 yards) a 2.4 inch difference in vertical and 0.5 inch horizontal difference in 10mph wind.
Needless to say a tight SD will give you more shots closer together, ES accounts for the "flier".
To put this in perspective though 20 fps ES is around 0.3 moa vert and the wind effect you can forget unless you are going for a world record.
Calculations for a 155 gr .308 Sierra Palma doing 2900fps vs 2880fps will result in (at 700 yards) a 2.4 inch difference in vertical and 0.5 inch horizontal difference in 10mph wind.
Needless to say a tight SD will give you more shots closer together, ES accounts for the "flier".
To put this in perspective though 20 fps ES is around 0.3 moa vert and the wind effect you can forget unless you are going for a world record.
im getting 39 sd on my 221 fireball. jeez i gotta get to work. didn't test my 7 mm rem mag yet. wonder how far off thatd be on that 221 at 400 yards.
Camac,
I agree that single-digit ES is the holy grail and not often achieved. On the same day that I shot the above series in .308, I shot the following 5-shot string with a 6BR and Sierra 107s. The group was a complete fluke, .095" at 100 yards. When I got home and dumped the chrono data, I could not believe it. If only they were all like that.
High Low Avg. ES SD
2978.8 2975.4 2977.2 3.4 1.7
I agree that single-digit ES is the holy grail and not often achieved. On the same day that I shot the above series in .308, I shot the following 5-shot string with a 6BR and Sierra 107s. The group was a complete fluke, .095" at 100 yards. When I got home and dumped the chrono data, I could not believe it. If only they were all like that.
High Low Avg. ES SD
2978.8 2975.4 2977.2 3.4 1.7
They are impressive figures Steve - never seen anything like that and that group size for the high BC bullets. Wow - I'd like my 6BR doing that.
I've had a few 5 shot strings show low ES (around 8-9) but then I always seem to get one here and there throw it out. SD is still good though
Toby - easy enough to do your own figures. Jump on JBM online or other ballistics program. enter your figures with zero scope height and 1yd sighting (that gets them as close to each other as possible) then plug in the two velocities separately for your given projectile from the library. It will tell you how far apart at the different ranges
I've had a few 5 shot strings show low ES (around 8-9) but then I always seem to get one here and there throw it out. SD is still good though
Toby - easy enough to do your own figures. Jump on JBM online or other ballistics program. enter your figures with zero scope height and 1yd sighting (that gets them as close to each other as possible) then plug in the two velocities separately for your given projectile from the library. It will tell you how far apart at the different ranges
I had not seen anything like it either and probably will not again from this gun. The rifle normally groups .3-.5 for five shots at 100. That group was just random chance. What astounded me was the combination of group and velocities. This group was like the old story of monkeys and typewriters. If you bang away long enough, something good will result.
If placed in context, as in the attached log excerpt, it looks more like an anomaly. The loads listed in the attachment are safe in my rifle and must be reduced for testing in another.
If placed in context, as in the attached log excerpt, it looks more like an anomaly. The loads listed in the attachment are safe in my rifle and must be reduced for testing in another.
i always seem to get a higher velocity on the cold bore shot. is that normal.
Low and consistent SD, AD, and ES are worthy goals if you intend to shoot the mid-ranges (600 yards). But don't fall into the trap of thinking they are the only goals. Accuracy and precision are what you are after, and after you shoot mid-range for a while you will be amazed how many times accuracy and low SD do not always come together in one load.
Point-blank Benchrest shooters seldom can tell you the SD of their loads. Many world-class shooters do not even own a chronograph or a powder scale. Instead, they tune their loads by actually shooting. Doing the same at the longer distances is always good advice. If you happen to find a load that is both accurate and has a low SD, you'll be a happy camper. But, if it doesn't work out that way, go with the load that shoots best and try to forget that it has an SD of 50.
JMHO
Ray
Point-blank Benchrest shooters seldom can tell you the SD of their loads. Many world-class shooters do not even own a chronograph or a powder scale. Instead, they tune their loads by actually shooting. Doing the same at the longer distances is always good advice. If you happen to find a load that is both accurate and has a low SD, you'll be a happy camper. But, if it doesn't work out that way, go with the load that shoots best and try to forget that it has an SD of 50.
JMHO
Ray
True enough that accuracy is the point. Short-range BR shooters shoot marginally stable bullet/twist combinations and pay scant attention to anything but group or score because that is what defines their game. When shooting from 600-1000 yards, more factors are relevant. Ballistic coefficient and velocity variation are significant factors. A 50 fps variation with a Sierra 107 produces over 9" of vertical at 1000 yards. Few long-range competitors are willing to ignore that much variation. The approach must be tailored to the application.
Steve
All true. But remember, a 50 fps variation with the SMK produces 9" of vertical on paper. It may not do that on the target. I shoot both 600 and 1000 yard Benchrest. I have had loads that showed very small SD on the chronograph and yet would not shoot smaller than 6" at 1000 yards. OTOH, I have had chronographed loads that looked terrible but would shoot 3" groups at 1000. I don't try to figure our why, I just take what the load will give me.
In my experience, a load that will shoot dots out to 300 yards will do well at 600 and probably even at 1000.
I wouldn't describe the point-blank Benchrest loads as marginally stable. I shoot a 6PPC at 600 yards with very good results as long as the conditions are good. A few years ago a friend of mine was shooting F-Class and he drove 100 miles to the range only to discover that he had brought the wrong rifle, his 6PPC. Rather than simply quit he decided to shoot it anyway. He cleaned every target out to 800 yards and only dropped out of the top 5 when his bullets key-holed at 1000.
Today, too many shooters live or die by the chronograph and ballistic charts. It wasn't too long ago that neither were available to long range shooters. They developed (tuned) a good accurate load but didn't have the slightest idea what the ES, SD, or AD was. They only guessed at the velocity.
Never say never and always avoid the word always.
Ray
All true. But remember, a 50 fps variation with the SMK produces 9" of vertical on paper. It may not do that on the target. I shoot both 600 and 1000 yard Benchrest. I have had loads that showed very small SD on the chronograph and yet would not shoot smaller than 6" at 1000 yards. OTOH, I have had chronographed loads that looked terrible but would shoot 3" groups at 1000. I don't try to figure our why, I just take what the load will give me.
In my experience, a load that will shoot dots out to 300 yards will do well at 600 and probably even at 1000.
I wouldn't describe the point-blank Benchrest loads as marginally stable. I shoot a 6PPC at 600 yards with very good results as long as the conditions are good. A few years ago a friend of mine was shooting F-Class and he drove 100 miles to the range only to discover that he had brought the wrong rifle, his 6PPC. Rather than simply quit he decided to shoot it anyway. He cleaned every target out to 800 yards and only dropped out of the top 5 when his bullets key-holed at 1000.
Today, too many shooters live or die by the chronograph and ballistic charts. It wasn't too long ago that neither were available to long range shooters. They developed (tuned) a good accurate load but didn't have the slightest idea what the ES, SD, or AD was. They only guessed at the velocity.
Never say never and always avoid the word always.
Ray
i ran 10 shots threw my ced m2 chrono out of my 260. i dont know what the diffrent deviations are but my slowest shot was 2758 and my fastest was 2765. i was super happy and that resulted in a 1.2 ctc group at 400 yds
above post should say 300 yd
Cheechako, I use a 100yd range at home for developing loads and have found I can (9 times out of 10) develop a load for the longer distances (up to 1000) at 100 with chrono. I have more recently added 300 yard range but find the wind beats me around too much to develop the load easily (I live in a windy place with 15-25 knot winds every day). I can't say I have seen too many of my loads that group better at 300 than at 100 in my conditions (but that may be my lack of skill). If they do I put it down to variations due to statistical probability - a bit like Steves ES above.
If it groups well at 100 and chronos well it tends to work well for me - but then I am not shooting 3 inch 1000 yard groups.
I agree -certainly chronographing alone and low ES doesn't mean it will group well but combine it with small 1,2 or 300 yard group sizes and I believe you will get a good long range load - I may be wrong so I don't discount it (but I haven't seen any evidence in my own techniques). I only enjoyed long range shooting (and hence participated) after my chrony arrived, I soon jumped from 300 to 600 to 1000 and my loading skills improved dramatically.
The chrony has helped me on numerous times after seeing a flier to check and see tha it is just outside my velocity range. It also helps define the load more accurately and gives me pretty clear velocity "boundaries". I check velocity against impact for every shot for this reason.
The 1/10 load that fails at 1000 but works for me on chrono and 100yds is generally due to stability or bullet failing or other explainable reason.
Toby - I nearly always get lower velocities on my first few shots - do you put a patch down before firing?
If it groups well at 100 and chronos well it tends to work well for me - but then I am not shooting 3 inch 1000 yard groups.
I agree -certainly chronographing alone and low ES doesn't mean it will group well but combine it with small 1,2 or 300 yard group sizes and I believe you will get a good long range load - I may be wrong so I don't discount it (but I haven't seen any evidence in my own techniques). I only enjoyed long range shooting (and hence participated) after my chrony arrived, I soon jumped from 300 to 600 to 1000 and my loading skills improved dramatically.
The chrony has helped me on numerous times after seeing a flier to check and see tha it is just outside my velocity range. It also helps define the load more accurately and gives me pretty clear velocity "boundaries". I check velocity against impact for every shot for this reason.
The 1/10 load that fails at 1000 but works for me on chrono and 100yds is generally due to stability or bullet failing or other explainable reason.
Toby - I nearly always get lower velocities on my first few shots - do you put a patch down before firing?
Ray,
I meant no disparagement of short-range BR shooters who, as a group, have contributed more to accurate shooting than any other. But, if a bullet keyholes above transonic, it was marginally stable. If the temperature dropped 40 degrees, it would not make 400 yards. A 118 BIB from an 18" twist barrel is not that stable.
I have shot thousands (over 6500) rounds of caliber .50 BMG through rifles to 1600 meters and beyond, from sea level to 14000 feet, -20f to +120f, and been a member of design teams from pistols to 155 howitzer. While it is a mistake to discount experience and valid anecdotal evidence, it is also a mistake not to measure results and attempt to explain them. As the old saying in QA goes, "That which does not get measured, does not get fixed." BTW, I was using Ingalls-based PC ballistics software in the early '80s.
Your comment about using "never" and "always" is a little hard to understand in that I used neither.
I meant no disparagement of short-range BR shooters who, as a group, have contributed more to accurate shooting than any other. But, if a bullet keyholes above transonic, it was marginally stable. If the temperature dropped 40 degrees, it would not make 400 yards. A 118 BIB from an 18" twist barrel is not that stable.
I have shot thousands (over 6500) rounds of caliber .50 BMG through rifles to 1600 meters and beyond, from sea level to 14000 feet, -20f to +120f, and been a member of design teams from pistols to 155 howitzer. While it is a mistake to discount experience and valid anecdotal evidence, it is also a mistake not to measure results and attempt to explain them. As the old saying in QA goes, "That which does not get measured, does not get fixed." BTW, I was using Ingalls-based PC ballistics software in the early '80s.
Your comment about using "never" and "always" is a little hard to understand in that I used neither.
Great ES for 10 shots.42769vette said:
Standard deviation (SD) gives an indication as to the how much variance there is from the average. A low SD but high ES (extreme Spread) means most shots are bunched close to the middle but may have one flier. For score shooters a low SD is more important. For group shooters the flier is important so ES should be used. Statistically speaking 3 shots cannot give you any real information, 5 is OK but you still occasionally have statistical errors such as Steves group above. 10 shots is much better.
If your chrony doesn't spit out SD Here is the way to calculate it.
1) Find the average of your results.
2) Take each individual velocity away from the average to give you the variation from the average.
3) Square these results individually and add them up.
4) Divide by the number of shots.
5) Square root this.
e.g. 2758, 2759, 2761, 2761, 2765.
1) average is (2758+2760+2761+2761+2765)/5 = 13805/5 = 2761
2) Differences are 3,2,0,0,-4
3) Squared and added (3*3)+(2*2)+(0*0)+(0*0)+(-4*-4) = 9+4+0+0+16 = 26
4) 26/5 = 5.2
5) square root of 5.2 = 2.28
SD = 2.28, ES = 7
Steve, camac
I think we agree more than we disagree. A load with a low, consistent, ES, SD, and AD, that shoots dots at 200 and 300 yards is very likely going to be a super load for 600 to 1000.
I always shoot a target when chronographing. If I get a big SD but a dot on the target, it deserves further testing, no matter how big the SD is. It's always hard to test and compare loads at the longer distances but it sometimes pays big dividends.
My comment about never and always was not aimed at anyone in particular. I was trying to respond to model 12 toby's initial question. There is no such thing as an ideal SD and you cannot let somebody tell you that a low SD is always good and a high SD is never good.
Ray
I think we agree more than we disagree. A load with a low, consistent, ES, SD, and AD, that shoots dots at 200 and 300 yards is very likely going to be a super load for 600 to 1000.
I always shoot a target when chronographing. If I get a big SD but a dot on the target, it deserves further testing, no matter how big the SD is. It's always hard to test and compare loads at the longer distances but it sometimes pays big dividends.
My comment about never and always was not aimed at anyone in particular. I was trying to respond to model 12 toby's initial question. There is no such thing as an ideal SD and you cannot let somebody tell you that a low SD is always good and a high SD is never good.
Ray
Ray, I don't discount anything - rifles are funny things. So many variables make it impossible to understand fully. More than one person will tell you the bullets can straighten after 2-300 yards. I just haven't seen it - but won't dicount it either.
Something else too - don't discount the accuracy of the chrono itself. Most are within 0.1-0.5% in ideal conditions but cloudy weather, poor light and not perfectly aligned can cause innacuracies. 0.5% of 3000fps is 15 fps after all.
Something else too - don't discount the accuracy of the chrono itself. Most are within 0.1-0.5% in ideal conditions but cloudy weather, poor light and not perfectly aligned can cause innacuracies. 0.5% of 3000fps is 15 fps after all.
One thing that I did learn from point blankers... One great group does not mean that much, it's the aggregate that matters.
To get back to Toby's question:
Some cartridges display excellent ES/SD numbers and some do not. The 6BR and 30BR are very easy cartridges to "tune". As Ray said, that does not mean they are not accurate.
I could not get my .223 788 to provide reliable SD below about 20. Investigating the bolt revealed that the ejector hole had been drilled too deeply and the firing pin was hitting and compressing the ejector spring for the last .080" travel. I drove a slightly oversize drill rod section about .1 long that was relieved on the firing pin hole side into the ejector hole. While in there, I polished the firing pin hole. The whole thing feels much better than before and the old rifle now often returns single-digit SD. But, the accuracy never changed. It shot <.5" before and still does. It is a 250 yard varmint rifle and the velocity variation never bothered anyone but me.
To get back to Toby's question:
Some cartridges display excellent ES/SD numbers and some do not. The 6BR and 30BR are very easy cartridges to "tune". As Ray said, that does not mean they are not accurate.
I could not get my .223 788 to provide reliable SD below about 20. Investigating the bolt revealed that the ejector hole had been drilled too deeply and the firing pin was hitting and compressing the ejector spring for the last .080" travel. I drove a slightly oversize drill rod section about .1 long that was relieved on the firing pin hole side into the ejector hole. While in there, I polished the firing pin hole. The whole thing feels much better than before and the old rifle now often returns single-digit SD. But, the accuracy never changed. It shot <.5" before and still does. It is a 250 yard varmint rifle and the velocity variation never bothered anyone but me.
sleepygator said:
Still on the original topic of standard deviation - I agree one great group actually doesn't mean much at all -It can give an indication but a great group can still happen even if the standard deviation of accuracy (not velocity this time) is high. It is similar to that 5 shot string of velocities you had earlier. Every so often the stars align and you get a short string with no fliers but it does not necessarily give an accurate indication of how the rifle, load and shooter is going. Many shooters tend to quote their "best ever" 3 shot group as an indicator of accuracy. More experienced competition shooters won't. It should indeed be an aggregate and/or at least 5 or 10 shot groups.
I think the irony in all this is a very accurate rifle with very low SD (e.g. accurate 6PPC shooting 10 shot groups in the "1's) would actually give a good indication with a 3 shot group. The lower the SD the lower the number of replicates needed to give you an idea.
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