Also be aware that electronic scales can often be susceptible to EMI (electromagnetic interference). A strong source of this is mobile 'phones, which chatter with the base stations periodically even when not on a call. They belt out pretty high instantaneous power levels if you are in a weak signal area. You can test this by placing a call, then waving it around your scales and maybe seeing the readings jitter about.
So put it on "aeroplane mode" or keep it well away from your loading area. Not in your pocket. Likewise keep the scales well away from broadband routers with WiFi, or laptops active on WiFi, though that is less of a problem.
Also when weighing out batches of powder, check the tare is zeroed, and the check weight reads correctly say every ten goes, or less frequently once you have gained confidence of any drift. Re-calibrate as necessary, but don't do it obsessively, sometimes a re-cal just starts you off again chasing your tail.
I've never found a need for a long warm up period if the room is kept at a stable temperature, no more than five minutes. If using a generally unheated space, turning on the heating then cracking on, the temperature will not be stable, and yes these sort of things can be sensitive to variations of temperature. It's not so much that the scale electronics need "warming up", it's mostly that the room itself is fluctuating.
If running on batteries (my preference, using a mains adapter risks introducing several other difficulties), use re-chargeables and keep them topped up. Don't rely on the low-battery indicator, They can begin to get erratic long before the indicator comes on.
Well worth learning the funny ways of digital scales, they are so much better than mechanical ones, which also can have their own different set of idiosyncrasies.
As for bullet weight variations, chrono the best and worst looking for extreme spread (but lots of other variables can affect that), or best simply do some grouping tests with your cherry-picked ones vs. a mixed selection of the supposed outliers, combining highest and lowest. Do it blind, i.e you don't know which is which until after you have assessed the targets. Package them identically, ask an assistant to take them out of sight, flip a coin, and label them heads or tails. See if you can tell the difference, were the cherry picked ones really any better, if so by how much ?
That's the only way you'll really know for yourself. Even then, what are you going to do with the information ? Start all over again with a different bullet, and maybe discover that it doesn't work any better, even though the weights you read on the scales seem tighter. There's so much more to it than that to design and make a good bullet, and frankly I think small bullet weight variations are one of the least important thing to obsess over, it's just that they are the easiest thing to measure.
It's how they actually shoot, on paper, that matters, assuming you have excellent technique, keep in practice, and are significantly better than your rifle's capabilities.
Just as inexpensive digital scales can let you measure powder to within say +/- 0.02 grains, used properly, whereas getting it correct within +/- 0.1 grains is quite good enough for almost all purposes. You can waste a lot of time chasing ultra-fine measurements if you have the tools, but it can also become very OCD, perhaps to very little gain, even at the highest levels of target shooting.
