Inquiring minds want to know. Are you willing to reveal how you get such low SDs and ESs with .223 ammo? I recently made a disappointing batch of ammo loaded for my Sunday "fun" range gun, a Howa-1500, with five-shot SDs averaging around 43 and a worst of 115. I decided it was because I was trying CCI-450 magnum primers for the first time in my .223 reloads. The other day I made a batch of 60 rounds in a specific effort to improve my SD numbers. I used my normal BR-4 primers and shot five shot groups with an average SD of 26, a best of 4.87 and a worst of 52.94. This isn't great, but it's a big improvement over the results using magnum primers.
I consider it acceptable for "fun" ammo. However, I actually used my best reloading techniques weighing the powder charge to .02gr. The components weren't my best, but they weren't junk either and included Sierra MK bullets rather than Berger and well prepared Lake City brass rather than Lapua. I expected, or at least hoped for, better results. I'm still disappointed that I can't get most of my SDs below 15 or perhaps even less.
I'd like to know your secret.
Again, a plot of SD vs MOA showed no correlation. In fact, the worst SD gave the smallest group.............. sigh.
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FWIW - in my hands, getting the ES down to the mid/upper teens for .223 using 80.5 and 90 gr bullets has not required anything secret or special. I'm very careful with brass prep, and I use the Redding Type S Match bushing dies with a Rock Chucker press. I have been using 2-2.5 thousandths neck tension on Lapua brass. I use Fed 205 primers (not 205M), so nothing special there. I don't neck turn, having "no-turn neck" chambers. I do weigh powder to approximately +/- half a kernel on an analytical balance, but this is probably grossly excessive. You can calculate the velocity spread that tight a range of powder weight accuracy will give and it's about 1 fps. I can't even measure velocity that accurately with my chronograph.
I think there are possibly some other reasons that people might struggle with getting low ES/SD values for .223 loads, that don't necessarily have anything to do with their reloading technique per se. I do believe it's important to weigh powder as precisely as possible in the small case, but it's also important that the charge weight itself be optimized, as well as the choice of powders. That is where I think actual load development may come into play.
Powders tend to exhibit optimal burn characteristics at slightly under MAX pressure. Selecting the right powder for the job includes thinking about barrel length, projectile weight, powder burn rate, and operating temperatures, to name a few things. Further, ensuring through proper load development and testing that you have, in fact, really "optimized" the charge weight is also critical. This cannot always be done solely by looking at group spread. It's also important to use velocity determination as part of that equation. Finally, even when the average velocity and short-range precision seem right where they need to be, it is possible for a load to exhibit poor ES/SD values.
In that event, it's probably a good idea to test different primers that cover a range of brisance. Sometimes, using a different primer can make all the difference in the world in ES/SD, even though the other load parameters may not change much. Some primers are simply better suited to some powders that are burning at a specific rate, which is largely dictated by the cartridge/bullet/barrel, etc. So if your ES is high, but everything else looks positive, try a different primer, it might help.
Edited to add one more thing about chronographs. I currently use a MagnetoSpeed. There are certain sub-optimal considerations that go along with that, but in general I have been very happy with it. I used to use a light sensor type chronograph. My experience with that was that the readings could vary significantly depending on ambient light (i.e. sunny vs cloudy), as well as exactly where the bullet passed over the sensor. At times, the chronograph would give a reading for a shot that I'm pretty sure was off, because of where the bullet passed over the sensor, or that perhaps a cloud went overhead. So it's also worth noting the possibility that the chronograph type and brand can potentially affect your readings.
In other words, it may not always be the load. This can be tested using two chronographs at the same time, or just by using a different chronograph for identically loaded rounds. In any event, you want to be sure your chronograph is giving you true readings before embarking on a potentially extensive process to minimize ES/SD. It's doesn't necessarily have to be some excruciating kind of test, but something simple as a one-time test, anything that will increase your confidence level regarding the chronograph readings if they are in doubt.