Once I get a load that proves accurate, i like to use 10 shots for ES for basic performance of the load Having said that, I pay a lot of attention to the first cold bore shot's velocity and then like to test cold bore performance at extended ranges for actual POI. I don't like putting any more rounds through my 6.5x284 (used for hunting) then I have to, but I would rather use 50% of the barrel life to develop a solid load that I can have absolute first shot confidence in then worry about wearing out my barrel.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
I shoot 5 shot groups for accuracy but for es/sd i shoot 3 shots. It gets you a ball park idea of what the loads doing. I hate wasting barrel life to get info that doesnt really need to be exact. Id say 5 shots are fine if your chrono is set up while your shooting accuracy groups but im funny that way. I allways seem to shoot better without the distraction of my chrono in front of me so i do sd/es as a seperate step.
Sometimes a person feels great with an ES of 9 and an SD of 3 or 4, but the next trip to the bench with the same load has an ES of 35 and an SD of 12 or 15 or more....Then the next time back to SD 7.....I keep a log of all these numbers on every trip to my bench especially while working up loads....Take an average over all the trips on different days and each time on that trip that you shoot that load. Run the numbers any sequence you like, throw out that ones from that real "hot" day or average it in.....In the end you will get a real good idea whats going to happen at the longer ranges....
My home range is 100 and 150 yards..That's where I chrono all my loads and do the majority of my load development......It is very true that a good ES and SD don't necessarily mean an accurate shooting load.....But it is false if you think you can have good groups without vertical stringing at 400, 500, 600 and beyond without good numbers over the chrono.....My "cheap" Shooting Chrony has it quirks (especially with extreme low sun angle at dusk [I shoot west]), but most light conditions can be controlled by shading the chrono...Cloudy days are best.....I see a small variation with different light conditions but end results are all relative to my numbers in the first place....In the end it must not be too far off because my drops out to 600 yards and beyond match almost perfect to my ballistics program [Berger's]....If you can work up a nice grouping load with a low ES/SD at 100 yards my bet says it will perform just as well at the longer ranges....I feel for my 600 yard stuff I like to keep the ES 30 or less for my 260s...This equates to around 2" verticals at 600 add this in to a 1/2 or 3/4 minute rifle at a 100 and you end up with 5 to 7 inch groups at 600..That is all the better my hunting rigs and I can shoot anyway with an occasional surprise with a three or four incher.......
The cold "fouled barrel" number is the most important to me and the SD based on that first shot over as many times I see this over the chrono is probably the best one to base what it will do at longer ranges...I have to drive 20 miles one way to the Rifle Club range where I can test at ranges up to 600 yards...When I get there I want to be able to dial up and shoot and not embarrass myself with a load that may or may not shoot...
The more shots fired to test anything, the more confidence there is it's what happens all the time. Note the chart showing number of shots per group vs. size. The percentages will apply to standard deviation as well as accuracy, or anything else.
another thing we have to consider is that barrels don't stay the same across hundreds of rounds of shooting--especially for barrel burning cartridges. so you might burn half the barrel life off getting that load *just* right, only to find that you're on the downside of barrel life and changes to the load, or at least the OAL as a minimum, have to be made... and tests begin again (?)
just sayin'... there is such a thing as too much testing, if you ask me.
I appreciate all the replies guys lots of good info. It sounds like the answer to my question is no there is no standard # of shots used by everyone to determine an accurate ES/SD. So when Joe or Bob say they have an ES of 10 nobody knows how they came to that conclusion. Joe might shoot 30 shots in 3 shot groups and average out the 10 groups while Bob might shoot 3 and call it good. Makes me wonder how useful it is to hear the results of Joe or Bob's tests without a detailed description of how they came to such results?