Never bad advise.
This is true with .308/7.62X51, but not .223/5.56, where case weights overlap a good bit.
With mixed cases for plinking/playing, I work up a load that is safe in the heaviest/least capacity cases used. I have seen the occasional case slip through (One in a few hundred), where the powder came up much higher in the neck when loading, and I have just pulled those and scrapped them.
For fine accuracy? Buy a lot of good brass, or sort Lake City military brass, or sort commercial brass.