Is that your best stats ever? Or just with this load?
I mean best ever-ever. Like have you ever shot a 3-shot 1SD/1ES, or a 3-shot 5SD/15ES?
I'm asking because I'm trying to gauge how accurate the rest of what you're doing is. I saw the Chargemaster+balance bit for charge weighing, but if 17.3SD/43ES is the best you've ever done, either you have a serious issue with your charges, or these loads in virgin brass is your first time taking stats.
If it's your first time recording this that's fine, just don't do it to yourself again until you've shot the cases, not worth the angst.
If you're really seeing that large of variation over 5 shots, there's something else going on here because it's just not that hard to get close enough charges to not see 50+ ES, and you're on the edge of that.