Inconsistent powder drop (or powder shacking out of brass as shell plate indexes). Variance in seating (not putting the same pressure on the handle. Lots of others including chrono. Crimping would be way down the list.
Do 20 or so measuring each powder drop, look for any spilled powder, adjust to make each as close as possible.
Measure COL on each round (different manufacturers have close tolerances.
Try to use the same pressure on each round.
Re-check with chrono.
How long have you been reloading? What powder and bullets are you using. AND must important is your ammo accurate. Having a small SD is nice but accuracy and reliability is what is important. Chrono factory loads and you might be surprised at the amount of variance.