For you folk who calculate your SD, are you calculating as Sample or Population? I've only recently been looking closer at my load data. On one of my accurate loads I got an ES of 13 and SD of 4. Is that really good or should I be looking for improvement?

Depends on your standards and sample size imo.

Most likely just fine to quit thinking about it. You didn't report the nunber of shots, but those numbers are typically quite good. Work on your shooting skills and wind reading.

In order to look at population you'd have to chrono every single round, that would get a bit tiresome. I would imagine most look at 5-20 and call it good. If you're careful in your loading you most likely won't get an outlier far enough away from the group avg that it won't still shoot pretty well. 13/4 are great numbers.

Interesting post.

What do you guys in the know consider the minimum for ES and SD.

For a parameter, a load that will consistently deliver sufficient accuracy to say make precision shot(cleanly take deer) at say 500 yards?

An sd under 20 will be more than effective at 500.

I look at ES, which is the difference between the high and low. And most shooters are looking at a small sample I want a tight ES, which would give you a low SD. Typically ES is about 3x to 4x times SD. In your case where ES is 13 and SD is 4, it's right about 3x times. With a low ES, you should be fine out to as far as you can shoot. I like to see sub 25 ES, and anything less than 25 is even better.

Yeah I should have mentioned this was only a sample of 5 shots at that powder charge. I opened a new jug of powder and wanted to compare velocity to the old batch. I had a suspicion that the new powder was a little hotter (confirmed) and had also loaded rounds in .1 increments down to .5 below the previous load. All of the five-shot groups were single digit SDs with low ES. So, looks like I'm in a good node?...but should take a larger sample size, and run the numbers as Sample rather than Population?

If you're going to keep fretting over it, you can chrono 10 rounds. If it were me, I would leave the load alone and go shoot it.

Speaking as someone who has some experience with statistics, anything less than a sample size of 100 isn't really going to give you statistically significant results, based on the number of variables that play into velocity of loaded ammo. That doesn't mean that the numbers you got were not accurate. It just means that statistically speaking, you should not rely on them to be accurate.
In answer to your other question, as you only have a population to measure, you should be running population statistics. Sample statistics are for when you only have a segment of data from a very large pool.

I have also found that there are some firearms that are actually a lot more tolerant, accuracy-wise, to velocity spreads than others. I am much more concerned with how the group looks than what the ES/SD is. The only number that really matters to me is Average Velocity so that I can calculate drops and then go verify DOPE.

I also want good groups at distance as well as 100 yards and in. The longer the distance the more ES of ammunition effects your drops. I agree on the general statements about statistics and sample size, the larger the sample the more meaningful the information.

What is your opinion of crimping Weatherby magnum cartridges and ES? I noticed in a 257 Weatherby using RL22 that tight neck tension and a slight crimp of .003 lowered both numbers a few digits. I will assume that the freebore of the Weatherby needs a little help.

I don't crimp rifle rounds like those. But if you trimmed the brass where they were all a consistent length with a consistent crimp, it can work. If you FL size the brass, there should be enough neck tension to hold the bullet in place without a crimp. If you find the right powder and load combination with throwing the powder charge to within .1 grains (or less), it will lower your ES numbers also. The freebore on the Weatherby rounds is what allows the higher speeds without the excessive pressure signs. Anytime you shorten the freebore, you will reach pressure sooner and limit your potential velocity. I've experimented with multiple rounds and calibers (same everything-powder, bullet, case, etc), and a short throat will reach pressure much sooner and generally not yield as much velocity as a longer freebore does. The last 2 we've tested were 7mm/300 WM and 308 Win.

Everything I have read says that if you have ES under 25 fps and SD in single digits you have exceptionally consistent ammunition.

The only cartridge I have seen that does better than that on a consistent basis is the 6PPC in a benchrest rifle with ammunition loaded using hand dies.

Just my .02,
LeonCarr

6br and 6.5x47 lapua both are equally as consistent as the ppc.

Then they are spooky consistent. My buddy's rifle (Stolle Panda action, Hart Barrel, McMillan Stock, Jewell Trigger) shoots in the .1s and he says many times he can fire 5 rounds over a chrono and all five rounds are the exact same velocity. Pretty amazing.

Just my .02,
LeonCarr