what are the load SDs? or how do I find them?Years ago I decided to change my way of searching for an accuracy load and stop making random changes that May not net me any gain in accuracy. On some rifles I would shoot 40 or more rounds before I saw any improvements.
So I decided to attack one thing at a time and try to eliminate one problem at a time so it would be easier to narrow accuracy down one thing at a time. I took the approach to start with things that were the most variable and get them constant.
Now I start with the load SDs to find out if I have chosen the right powder, case capacity, bullet weight and the primer. At this point I don't care about accuracy just the lowest SD. I can make minor changes and read the effects and then I know what is needed to lower SDs.
Once I have found the right combination, I know that the load its self is consistent. Then I start working on the accuracy by changing bullet styles and seating depths, maintaining the same bullet weights.
With this procedure I have found very accurate loads within 20 to 25 loads. this method has saved me much time and components and added barrel life. I even start with my preferred load while braking in the barrel and found that many times there were indications that I was on the right track even though the barrel was not fully broke in.
Other methods were hit and miss and occasionally I got lucky, but most of the time I just spend time and money an had to deal with frustration
of poor accuracy.
Doing it this way eliminates many of the other reasons for poor accuracy. (Like shooter error) because the chronograph doesn't care if you are having a bad day. And to answer your question I don't stop trying until I see no signs of improvement. Good SDs tell me that I have a good consistent powder burn and pressure that is not effected by any other factor that effects accuracy.
Just the way I test for accuracy loads
J E CUSTOM
How much time and effort do you give a bullet, powder.
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what are the load SDs? or how do I find them?
Ronald W Schaefer
Well-Known Member
I had my gunsmith turn me on to some great advice (after reloading for 40+ years). I was really trying to get Nosler Accubond bullet to shoot in my friend's .270, had gone through ladders with about five different powders, primers seating depths etc. and there was no help...all 1.25-1.5". Gunsmith checked the rifle over, said the problem was, I needed to solve for the bullet that rifle likes first. Pick a solid load out of the manual that works for the five or so bullets you want to test. One will clearly shoot better than others. Then work up the load with that bullet. I switched to Barnes TTSX and with no other changes it dropped to about .8 MOA. Now I select the bullets suitable for my purpose from various mfr. and shoot them using the same load. The one that shoots the best I proceed on with. Maybe swap out that Berger for Barnes or some other premium bullet.
Buzzsaw
Well-Known Member
I'm the anti ladder test Nazi. Lazy on my part, wasteful in my opinion. If you have a rifle which wont shoot .5"-.75" MOA with common popular loads other shooters have found. Get rid of it, cry once, get you a custom/semi custom rifle built or buy a Bergara Pro Series, Christensen, X-Bolt, hate to say it but even a Tikka. Midwest Shooters has a brand new, semi custom, .243, 8 twist, with Kreiger barrel for like $1500, What a great deal, scoot the 105 grainers to 1000 yards all day.
again, this is just MY opinion, whatever works for you is great with me.
again, this is just MY opinion, whatever works for you is great with me.
Earlybugle
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I first select a bullet and weight, then do some research on published accurate loads with that bullet. From that research, I select my first round component set (powder and charge weight, primer, and projectile) to test. Using those components I load up 4 round sets that are in weight increments of 0.7grains between each set (group). Normally I end up having 7-10 loads to fire 3 round groups with (the 4th test round is available if I failed to do my job shooting one of the prior three )
My groups will typically vary between 0.50 - 1.75 MOA. If the best first round group is .75MOA or less, I select the load with the best group and normally is it also the lowest m-velocity Standard Deviation (SD).
If the best group is 1/2MOA or better I jump to COAL adjustment. If still 3/4MOA or more, I change powders. If over a half MOA..... I will then reload and fire 5 round groups around the selected powder charge above and below, in increments of .01grains. Usually another 1/4MOA comes out of the group.
Finally I adjust COAL which often yields another 1/8MOA.
My groups will typically vary between 0.50 - 1.75 MOA. If the best first round group is .75MOA or less, I select the load with the best group and normally is it also the lowest m-velocity Standard Deviation (SD).
If the best group is 1/2MOA or better I jump to COAL adjustment. If still 3/4MOA or more, I change powders. If over a half MOA..... I will then reload and fire 5 round groups around the selected powder charge above and below, in increments of .01grains. Usually another 1/4MOA comes out of the group.
Finally I adjust COAL which often yields another 1/8MOA.
Or your scope could be broke, loose rings, loose bases, or too tight on the rings....just my extra 2cents
To determine the Standard Deviation of a load, you'll need a chronograph. I shoot five rounds of the same load over mine, record the results and then consult a statistics website that does the calculation for me. I abysmally failed Stats in college, so I don't know how to calculate barely anything "statistical."
I go to the following website, input "5" for the number of rounds fired and input the five velocities. Click on "Calculate" and enjoy the results. The numbers you'll get back are expressed in scientific notation, but that's not a problem. You'll see the highest, lowest, mean (average), median (this is the number that most interests me) and Standard Deviation.
I am interested in the median because it's a better number than is the average. The median is the number that has an equal number of data points both above and below the "middle" of the data population. The average can be misleading. If you have nine velocities that are what you'd expect and one that's 1,000,000 fps, the average is going to be badly skewed upward. Of course, you're never going to see a muzzle velocity of a million fps, but you get the idea.
I fired five rounds over a chronograph; the velocities returned were 2715, 2682, 2704, 2721 and 2715. The mean is 2707, median is 2715, high is 2721, low is 2682. The Standard Deviation was calculated to be 15.5 fps; the Extreme Spread is 39. Using the median of 2715, the muzzle energy calculates to be 4092 foot-pounds. I get the KE from a ballistics calculation website, not from the link below. When your SD is very low, that means your muzzle velocities are very consistent. It means your bullets have a good chance of finding the same hole over and over again, lacking some sort of outside influencer like a gust of wind or a massive earthquake just as you fire the round. A high SD means your bullet velocities are wildly jumping up and down; you have very little consistency which manifests itself as large groups about which you'd not bother to write home.
http://www.physics.csbsju.edu/stats/cstats_NROW_form.html
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Ronald W Schaefer
Well-Known Member
Get the Caldwell chrony and iPhone app...you fire your five rounds and it records and calculates everything for you...more data than you need and you can save it, calculate energy, records temps and HG everything...not too spendy either.
J E Custom
Well-Known Member
You have to use an instrument like a chronograph to give you actual velocities and use these velocities to establish the average of all shots fired. (Standard Deviation) The lower the SDs, The more consistent the Load. This can/does have an effect on accuracy but it is just one part of the accuracy equation.
In my opinion it is the first step in finding an accurate load.
J E CUSTOM
ntsqd
Well-Known Member
I never trust a Statistic that I didn't make up myself.
Copied several of your processes into my notes for future ref. thank y'all!
Anxiously awaiting the delivery of a ProChrono DLX myself....
With all this talk about bullets, powder, primers & SD's to find the best load, what about brass prep? I realize most new brass needs to be sized and maybe trimmed to begin with but I'm curious about sorting the brass, neck turning, annealing, etc. Is every bit of that brass prep absolutely necessary to do before the first shot is fired? Or is that recommended to do after your on to a good load?
Standard deviation you need to shoot loads over a chronograph and it will give you the Es your extreme spread or Sd standard deviation
Joefrazell
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Yes sorry I should have stated I'm using a magnetto speed and the SD are high. Like 30 fps for 3 rnds. I'm using wlrm primers. Thinking of switching to cci250 and seeing if that makes a difference with the sd
The problem I've read about with the MagnetoSpeed chrono is that it can sense the combustion gases, which are considerably higher than the velocity of the bullet. It has to be precisely mounted, or you may get that problem.
I'm cheap, so I use the ProChrono and have it precisely aligned so I do not hit it with a bullet. I put 5/32" O-rings on the uprights, put little binder clips on them so I can see them from 15 feet, put clips on the skyscreens and use a golf shaft to aim the chrono at the target. I align everything and once that's all done, I very rarely ever fail to capture a shot. The clips are placed high enough up the uprights to allow for plenty of space for the bullet to pass over the body of the instrument. The bullet's path is represented as the blue line. Works 99.99% of the time...
To keep too much sunlight from blinding the sensors if I'm still shooting when the sun gets close to directly overhead, I cut a piece of smoked Plexiglas to serve as sunglasses for them. That also works to near a 100% success rate.
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