I have been chasing around a pressure issue and ran out after work Friday to test my newly reworked brass compared to some new brass and then out for a hunt.
My thought was to try some loads in the reformed brass to see if I was still getting pressure and then back down the charge etc until the pressure signs went away.
Long story short, the pressure was still there and the speeds high. All the pressure loads were over 3000. I backed down and played with 215 and 210 primers. What seemed to work was 56 grains and 210 primer. At .005 off the lands the pressure signs were mostly gone and the speeds:
with 55.5 grains and 215 primer, .005
None of this equated to a great group down range at 100. My hold sucked honestly and everything was under 1". I was rushing and not taking the time to shoot precision but really I wanted to try and reduce pressure to a level that seemed OK and start over.
Does SD and ES have anything to do with tight groups? I am just being stubborn and worrying too much about velocity when I should just back it down to 2900 to 2950 and look for SD/ES and that give me an accuracy node? I want to get as much velocity as I can with decent accuracy (.5) or less but kind of wondering if I am going about it all wrong. I used to not worry about the chrono, shot the load until no pressure sign, found seating the gave accuracy, called it a day.
I have not used a chrono in a while actually. I will tell you how my load development went with my 338 LM.
I loaded up the test loads, shot them and found the most accurate load out of them all. Went .5 gr above and below that load to see if I could squeeze more accuracy out. Took the most accurate out of those and played with the seating depth a little to see if I could tighten it up anymore. I was doing all of this out at 500 yards after the first initial testing though and on calm days.
I loaded up my final load and zeroed it at 100 yards. I went out and verified my drops starting at 300 yards all the way back to a mile. Played with the velocity in shooter along with a few other tweeks in shooter to match my drops exactly. I dont know what my ES and SD is. Heck, I don't even know what my velocity from a chrono actually is. But man my gun is shooting some tight groups out at 1000 and beyond and I couldn't be happier.
If your gun is shooting accurate out at long range and doing so consistently, I dont really believe that ES and SD matter a whole lot. Consistency of accuracy is my main thing that I worry about.
You do need to make sure that you are not shooting at too high of a pressure though. That can mess with how consistent you are and the life of your brass. Find a node that isn't over pressured and stretch it out to see if it is consistent in the accuracy department. Remember that speed isnt everything. If you have a 2900-2950 fps load that shows no pressure and shoots consistently accurate, I would take that over a half way decent load that goes 3000 fps anyday.
Your load being consistently accurate will do VOLUMES to boost your shooting confidence. And confidence is a big deal in this sport.
I am shooting a 300 gr berger out of a 26" tube and to match my drops, shooter says that my velocity is 2810 fps. I am shooting 93gr of H1000. I dont get any ejector marks on my brass or any sign of pressure unless I shoot in temps 80 degrees or above so I am right on the edge of the pressure/no pressure area. I bet if I chrono'd my load it would be pretty close to the 2810 fps but I dont know.
I tend to follow Korhil78's school of thought. Find something that works first and foremost. I use my chrono when I am testing for max just to get an idea where I am at (and to see if something is wonky).
After that, I won't hook it up again until I have a load developed that I am happy with. I do this for two reasons. One, it is another datapoint to confirm drops, downrange energy, etc. Two, if something gets out of whack in the future I have a baseline to see if there is a major change in velocity.
Basically, I use the chrony to analyze a good load, not as a predictor of one.