I pulled out a few hundred of mine, and did a random check. Most were withing .005", but a few outliers up to .010". I figured I could blame the projectile, so checked those. Nope, all within .001", mostly better (not bad for cheap stuff).
Assuming the dies are set up correctly, that leaves -
-Case lengths inconsistent
-trash/shavings/dirt
-inconsistent primer seating
-inconsistent ram pressure in seating and/or crimping
Sure enough, I just checked my stash of cases and found several that were .010" longer than the median.
for a test - do each stage as a batch, measure between batches
Lock down your setup, don't adjust again.
Go back and measure some cases and projectiles, find 10 -20 that are exactly same length (after deprime,sizing, expanding).
prime, measure, drop powder
seat, measure
crimp seperate step, measure
Take measurement notes on each step