The case is going to elongate slightly when you back the die off to the point where the die shoulder isn’t contacting the case shoulder. Take that case and chamber it in your gun with the striker removed. If it closes tight, move the die down slightly and size it again, measuring each time, until you size one to fit. The resulting case is a maximum length.
If you’re too course with your die adjustments, you may overshoot it, but thats ok, because you have more cases to repeat the process.
If you do it right, you find sized a case where the case shoulder is just touching the chamber shoulder when you close the bolt. Your target for future cases would be .001-.002 short of that.
Edit:the hornady cases I’ve measured are usually within .001-.002 of a go gauge. If your chamber is right down near go, what you’re seeing would be perfectly normal, and bumping them back to factory would be fine.
