As "woods" posted above, I too have found variations in bullet weight and length which transferred into a different COAL to maintain a target "gap". I also found a change in bullet ogive in different boxes of Partitions, which reflected there differing bullet length.
To add to this - in some cases, particularly OTM style bullets, one could go nuts trying to figure out the variations in OAL that results from different nose lengths of the bullets. I loaded a few hundred 75gr Hornady BTHP bullets in 5.56 the other night; ogive length was very consistent, but OAL varied from 2.245" to 2.260", and one box required deeper seating than the other to stay within magazine length. If I had been going by OAL alone, it could have been very frustrating, and I've had ended up with two different batches of ammo at two distances off the lands.
