This is more of an issue with cartridges that have less case volume under the bullet with more variation in OAL (9mm is the most sensitive due to the low case volume and great OAL variation of 1.010" to 1.169").

You are on the correct track with bullet seating depth rather than OAL. Some earlier loading manuals listed bullet seating depth. But it is very easy to calculate. A resource that will assist you can be found here.