As brass gets reloaded several times, it gets less malleable and often dies need to be turned in a little. Cases shot in a different rifle may also require more sizing.
I once bought a set of 6mm Rem dies from a reputable manufacturer that were actually warped at the factory during heat-treating. Loaded rounds rolled across a table resulted in bullet noses going around in a circle. Rounds didn't chamber. The die was returned and the new one was fine, but now I always roll my first reloads from a new die set.