IMtheNRA,
Yes, I do load .223. I am, as you might guess, an experimenter, so I seldom settle on one load over the long haul. As a result, I can't tell you that something that gave me a certain result with cases, primers, bullets and powder at one time would give me that same result with different lots today.
The other thing is, when you collect a lot of data over time you get some unrepresentative results that are randomly better or worse than usual. On that point, I have had small groups (5) with SD's as low as 0 after rounding to the nearest whole foot per second. Do I expect that to be repeatable? No. Do I expect it to hold up with a more reasonable sample size? No. It just randomly happens once in a long while and may as easily be due to random chronograph errors that happen to neutralize some velocity variation as due to getting an actual number randomly that small.
I also have to point out that small SD doesn't automatically mean you get the smallest groups. You still need to be on a barrel time sweet spot for that, too.
In general, I don't look at SD's in fps, but in % of the mean (average) velocity for the load. You see a lot of folks chronographing rifles report SD's in the 0.5-1% range. For a 2700 fps load, that's 13.5-27 fps. I like to try try for 0.3% and figure there is room for improvement if I haven't got there yet. For a 2700 fps load, that's an ES of 8 fps. For a 3200 fps load, it is almost 10 fps.
I've achieved numbers below 0.3%, but I don't really trust optical chronographs to be accurate enough to make accurate SD determinations smaller than that without really large sample sizes. Really large sample sizes often take long enough to shoot that light and other ambient conditions have changed during the session, adding another variable into the mix.
This year I bought a LabRadar chronograph which claims a minimum of 0.1% precision, so I should be able to get some tighter SD's that are real using that. I just haven't had a lot of range time this year, and that hinderrf experimenting with it.
There are things you can do to cut SD down: controlling firing conditions and barrel temperature. Choosing the right primer. I've had some really low .223 SD's using the inexpensive Russian Tula KVB556 primer, which is a military sensitivity spec primer for floating firing pin guns like the AR. I bought a slip of 5,000 at one point, and that lot, at least, has proved very, very consistent. Tighter than Federal 205M's, even. The only problem with them is it takes some extra effort to seat them.
For seating, I've been using the K&M Primer Gauge tool whenever really tight results were what I was after. For all small primers except the 205M I go 0.003" below the point of anvil contact with the floor of the primer pocket. For the 205M, Federal recommends 0.002" below contact to set the bridge, so I've been using that, though I haven't notice real difference with that an -0.003" with it. The K&M tool is the only one that gives results individualized for the particular case and primer and that is measured. But man is it slow going priming that way. I'd never bother for my 200 and 300 yard service rifle match loads. Only the 600 yard slow fire loads get that kind of tender care.
I always deburr flash holes anymore. I've proven to my own satisfaction that it makes little difference with easily ignited stick powders, but with older ball powder formulations and loads that don't fill a case well, in particular, it can reduce SD measurably. So now I just make it a part of routine case prep so I don't have to wonder if I mismatched a case with a wrong powder.
For cases I anneal and either lightly brush the insides with a bore brush in my drill press at low speed after resizing and doing any trimming that may be needed. The I apply a little graphite and alcohol solution and let that dry before charging and seating. I skip the graphite step with moly-coated bullets.
For super tight loads of stick powders, I use a volumetric/weight hybrid powder dispensing technique. I put the primed, empty case on the scale, tare it, dispense the powder volumetrically, then look at the charge weight by putting the charged case back on the scale. If I hit the right charge weight, it's a go. Otherwise, I dump it, check there are no stray grains left behind in the case, then do it over again. I'm using the JDS QuickMeasure for this as it is the most consistent stick powder measure I've tried and gives me the fewest re-do's. Nonetheless, this is tedious. I could also charge small and trickle up, but that takes time, too. Nonetheless, I should try to find time to compare how the two approaches perform.
The rationale behind that dispensing approach is the number of reports from folks getting better accuracy from volumetrically dispensed loads than from weighed ones with some powders, and particularly with stick powders. Apparently a heavy charge from a volumetric dispenser tends to be more tightly packed powder, and more tightly packed powder tends to burn more slowly which, in some instances can compensate for the charge weight error nicely. In others, though, that doesn't work out, so this has to be tested with your load to see if it holds up or not. But anyway, I figure that if both the volume and the weight are correct, I've got both bases covered, and if I take a load into production for the season's shooting, I can figure out which is better to do then.
Obviously, if your barrel temperature, bolt closing to firing time and level of bore fouling are kept constant, that helps, too, but probably isn't practical for match shooting where you can't normally control all those things.
